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Cardiff University
1.
Mexis, Meletios.
Optoelectronic properties of InAs GaAs columnar quantum dot laser diodes.
Degree: PhD, 2008, Cardiff University
URL: http://orca.cf.ac.uk/54843/ 
;
http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.584395
► In this thesis results are described with the aim of examining the optoelectronic properties of InAs/GaAs columnar quantum-dots and comparing them with those of more…
(more)
▼ In this thesis results are described with the aim of examining the optoelectronic properties of InAs/GaAs columnar quantum-dots and comparing them with those of more conventional self-assembled quantum-dots. The polarisation properties of a set of columnar quantum-dot samples — of varied aspect ratio and In compositional contrast between the rod-shaped dot and the surrounding 2-D layer — are studied. For this investigation a new method to obtain the ratio of the fundamental TE/TM optical response using edge photo-absorption spectroscopy is proposed, which corrects for the polarisation-dependent features of the experimental set-up. The method is verified by application to compressive and tensile strained InGaP quantum well structures, where the results are in agreement with known ratios of the band-edge matrix elements. When applied to columnar quantum-dot samples it is shown that the TE/TM optical response depends on the dot aspect ratio and the In compositional contrast. A polarisation-independent photo-absorption is illustrated for a columnar quantum-dot of an aspect ratio (dot's height over diameter) 3.51:1, which is desired for use in semiconductor optical amplifiers. For the columnar dot of an extremely high aspect ratio, 7.5:1, a room temperature TM-dominant polarisation lasing emission is observed. By studying the Quantum-Confined Stark Effect, a dramatic enhancement of the Stark shift amplitude is shown for columnar quantum-dot samples of an increased dot aspect ratio from 0.63:1 up to 1.12:1, which may have application in optical modulation/switching. For a higher aspect ratio columnar quantum-dot the shift of the band edge of the photo-absorption spectra is reduced dramatically and this has been attributed to an overall effect where the observable shift becomes the result of higher energy transitions, where their oscillator strength change very rapidly within the studied range of field. For the highest aspect ratio dot, i.e. of aspect ratio 10:1, there is no any observable shift.
Subjects/Keywords: 535
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APA (6th Edition):
Mexis, M. (2008). Optoelectronic properties of InAs GaAs columnar quantum dot laser diodes. (Doctoral Dissertation). Cardiff University. Retrieved from http://orca.cf.ac.uk/54843/ ; http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.584395
Chicago Manual of Style (16th Edition):
Mexis, Meletios. “Optoelectronic properties of InAs GaAs columnar quantum dot laser diodes.” 2008. Doctoral Dissertation, Cardiff University. Accessed September 21, 2019.
http://orca.cf.ac.uk/54843/ ; http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.584395.
MLA Handbook (7th Edition):
Mexis, Meletios. “Optoelectronic properties of InAs GaAs columnar quantum dot laser diodes.” 2008. Web. 21 Sep 2019.
Vancouver:
Mexis M. Optoelectronic properties of InAs GaAs columnar quantum dot laser diodes. [Internet] [Doctoral dissertation]. Cardiff University; 2008. [cited 2019 Sep 21].
Available from: http://orca.cf.ac.uk/54843/ ; http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.584395.
Council of Science Editors:
Mexis M. Optoelectronic properties of InAs GaAs columnar quantum dot laser diodes. [Doctoral Dissertation]. Cardiff University; 2008. Available from: http://orca.cf.ac.uk/54843/ ; http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.584395
University of Leicester
2.
Lawrence, James.
Differential absorption LiDAR for the total column measurement of atmospheric CO2 from space.
Degree: PhD, 2012, University of Leicester
URL: http://hdl.handle.net/2381/10379
► Since the beginning of the industrial revolution (1750 to 1800) the Earth’s atmospheric composition has undergone significant change as a result of human activities, in…
(more)
▼ Since the beginning of the industrial revolution (1750 to 1800) the Earth’s atmospheric composition has undergone significant change as a result of human activities, in particular the burning of fossil fuels. As a consequence the atmospheric concentrations of a number of gases known to be influential to the Earth’s climate have increased far beyond natural levels. Atmospheric gases such as carbon dioxide which naturally exist in the Earth system have increased in correlation with anthropogenic emissions. The effect of this perturbation on the Earth system has been predicted through computer simulations to have undesirable consequences on the Earth’s future climate. The present measurement systems for atmospheric carbon dioxide have limited spatial coverage and temporal resolution which restricts their ability to accurately attribute observations of atmospheric composition to particular terrestrial sources and sinks. This inability to accurately locate and quantify the key carbon dioxide sources and sinks in the terrestrial and marine biospheres is hindering the understanding of the processes that are driving the Earth’s natural uptake of approximately half of the anthropogenic carbon dioxide emissions. With such uncertainty it is currently unknown precisely how the Earth’s climate will respond to global warming in the future. Through computer simulation it has been demonstrated that improving the spatial distribution of global measurements of atmospheric carbon dioxide is likely to advance the present understanding of the Earth’s terrestrial sources and sinks. Regions that require particular improvement in measurement coverage are the southern oceans owing to a lack of landmass on which to site instruments, and much of the tropics because of difficulties in locating instruments in some of the worlds more politically unstable regions. Satellite remote sensing instruments which measure atmospheric carbon dioxide from low Earth orbit provide some coverage of these sparsely sampled locations, however cloud cover often prevents measurements being made (particularly in the tropics), and limited latitudinal coverage caused by current instruments using passive remote sensing techniques prevents measurements at very high and low latitudes (including much of the southern ocean during local winter). An alternative remote sensing technique has been proposed in the scientific literature for measuring atmospheric carbon dioxide concentrations using laser emissions from a satellite platform known as total column differential absorption LiDAR (TC-DIAL). The TC-DIAL technique has been identified as having the theoretical potential to meet the coverage and precision requirements to greatly aid in identifying and quantifying terrestrial carbon dioxide sources and sinks. The TC-DIAL technique has the potential to achieve these goals largely owing to its unique capabilities of being able to make measurements during both the day and night and at all latitudes with a footprint which may be small enough to see between patchy cloud cover in…
Subjects/Keywords: 535
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APA (6th Edition):
Lawrence, J. (2012). Differential absorption LiDAR for the total column measurement of atmospheric CO2 from space. (Doctoral Dissertation). University of Leicester. Retrieved from http://hdl.handle.net/2381/10379
Chicago Manual of Style (16th Edition):
Lawrence, James. “Differential absorption LiDAR for the total column measurement of atmospheric CO2 from space.” 2012. Doctoral Dissertation, University of Leicester. Accessed September 21, 2019.
http://hdl.handle.net/2381/10379.
MLA Handbook (7th Edition):
Lawrence, James. “Differential absorption LiDAR for the total column measurement of atmospheric CO2 from space.” 2012. Web. 21 Sep 2019.
Vancouver:
Lawrence J. Differential absorption LiDAR for the total column measurement of atmospheric CO2 from space. [Internet] [Doctoral dissertation]. University of Leicester; 2012. [cited 2019 Sep 21].
Available from: http://hdl.handle.net/2381/10379.
Council of Science Editors:
Lawrence J. Differential absorption LiDAR for the total column measurement of atmospheric CO2 from space. [Doctoral Dissertation]. University of Leicester; 2012. Available from: http://hdl.handle.net/2381/10379
Heriot-Watt University
3.
Lucotte, Bertrand M.
Fourier optics approaches to enhanced depth-of-field applications in millimetre-wave imaging and microscopy.
Degree: PhD, 2010, Heriot-Watt University
URL: http://hdl.handle.net/10399/2323
► In the first part of this thesis millimetre-wave interferometric imagers are considered for short-range applications such as concealed weapons detection. Compared to real aperture systems,…
(more)
▼ In the first part of this thesis millimetre-wave interferometric imagers are considered for short-range applications such as concealed weapons detection. Compared to real aperture systems, synthetic aperture imagers at these wavelengths can provide improvements in terms of size, cost, depth-of-field (DoF) and imaging flexibility via digitalrefocusing. Mechanical scanning between the scene and the array is investigated to reduce the number of antennas and correlators which drive the cost of such imagers. The tradeoffs associated with this hardware reduction are assessed before to jointly optimise the array configuration and scanning motion. To that end, a novel metric is proposed to quantify the uniformity of the Fourier domain coverage of the array and is maximised with a genetic algorithm. The resulting array demonstrates clear improvements in imaging performances compared to a conventional power-law Y-shaped array. The DoF of antenna arrays, analysed via the Strehl ratio, is shown to be limited even for infinitely small antennas, with the exception of circular arrays. In the second part of this thesis increased DoF in optical systems with Wavefront Coding (WC) is studied. Images obtained with WC are shown to exhibit artifacts that limit the benefits of this technique. An image restoration procedure employing a metric of defocus is proposed to remove these artifacts and therefore extend the DoF beyond the limit of conventional WC systems. A transmission optical microscope was designed and implemented to operate with WC. After suppression of partial coherence effects, the proposed image restoration method was successfully applied and extended DoF images are presented.
Subjects/Keywords: 535
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APA (6th Edition):
Lucotte, B. M. (2010). Fourier optics approaches to enhanced depth-of-field applications in millimetre-wave imaging and microscopy. (Doctoral Dissertation). Heriot-Watt University. Retrieved from http://hdl.handle.net/10399/2323
Chicago Manual of Style (16th Edition):
Lucotte, Bertrand M. “Fourier optics approaches to enhanced depth-of-field applications in millimetre-wave imaging and microscopy.” 2010. Doctoral Dissertation, Heriot-Watt University. Accessed September 21, 2019.
http://hdl.handle.net/10399/2323.
MLA Handbook (7th Edition):
Lucotte, Bertrand M. “Fourier optics approaches to enhanced depth-of-field applications in millimetre-wave imaging and microscopy.” 2010. Web. 21 Sep 2019.
Vancouver:
Lucotte BM. Fourier optics approaches to enhanced depth-of-field applications in millimetre-wave imaging and microscopy. [Internet] [Doctoral dissertation]. Heriot-Watt University; 2010. [cited 2019 Sep 21].
Available from: http://hdl.handle.net/10399/2323.
Council of Science Editors:
Lucotte BM. Fourier optics approaches to enhanced depth-of-field applications in millimetre-wave imaging and microscopy. [Doctoral Dissertation]. Heriot-Watt University; 2010. Available from: http://hdl.handle.net/10399/2323
Heriot-Watt University
4.
Warbuton, Ryan Ellis.
Infrared time-correlated single-photon counting.
Degree: PhD, 2008, Heriot-Watt University
URL: http://hdl.handle.net/10399/2259
► This Thesis investigates near infrared ( ~ 1550 nm) time-correlated singlephoton counting, studying the single-photon detectors and some of the potential application areas. Custom designed…
(more)
▼ This Thesis investigates near infrared ( ~ 1550 nm) time-correlated singlephoton counting, studying the single-photon detectors and some of the potential application areas. Custom designed and fabricated InGaAs/InP single-photon avalanche diode detectors were characterised. Our devices yielded single-photon detection efficiencies of ~10 %, timing jitter of 200 ps, and noise equivalent power comparable to the best commercially available avalanche photodiodes operated in Geiger-mode. The afterpulsing phenomenon which limits the maximum count rate of InGaAs/InP single-photon avalanche diodes has been investigated in detail and activation energies calculated for the traps that cause this problem. This was found to be ~250 meV for all the devices tested, despite their differing structures and growth conditions, and points to the InP multiplication region as the likely location of the traps. Ways of reducing the effects caused by the afterpulsing phenomenon were investigated and sub-Geiger mode operation was studied in detail. This approach enabled freerunning, afterpulsing-free operation at room temperature of an InGaAs/InP singlephoton avalanche diode detector for the first time. Finally, time-of-flight photon counting laser ranging was performed using both singlephoton avalanche diodes and superconducting nanowire single-photon detectors. The use of the latter resulted in a surface to surface depth resolution of 4 mm being achieved at low average laser power at an eye-safe wavelength of 1550 nm.
Subjects/Keywords: 535
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APA ·
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APA (6th Edition):
Warbuton, R. E. (2008). Infrared time-correlated single-photon counting. (Doctoral Dissertation). Heriot-Watt University. Retrieved from http://hdl.handle.net/10399/2259
Chicago Manual of Style (16th Edition):
Warbuton, Ryan Ellis. “Infrared time-correlated single-photon counting.” 2008. Doctoral Dissertation, Heriot-Watt University. Accessed September 21, 2019.
http://hdl.handle.net/10399/2259.
MLA Handbook (7th Edition):
Warbuton, Ryan Ellis. “Infrared time-correlated single-photon counting.” 2008. Web. 21 Sep 2019.
Vancouver:
Warbuton RE. Infrared time-correlated single-photon counting. [Internet] [Doctoral dissertation]. Heriot-Watt University; 2008. [cited 2019 Sep 21].
Available from: http://hdl.handle.net/10399/2259.
Council of Science Editors:
Warbuton RE. Infrared time-correlated single-photon counting. [Doctoral Dissertation]. Heriot-Watt University; 2008. Available from: http://hdl.handle.net/10399/2259
Heriot-Watt University
5.
Merkl, Michael.
Schrodinger, Dirac and beyond : non-Abelian gauge fields in ultracold quantum gases.
Degree: PhD, 2010, Heriot-Watt University
URL: http://hdl.handle.net/10399/2329
► In this thesis, optically induced non-Abelian gauge fields in ultracold atoms are investigated. Gauge fields can emerge in the equation of motion for the optically…
(more)
▼ In this thesis, optically induced non-Abelian gauge fields in ultracold atoms are investigated. Gauge fields can emerge in the equation of motion for the optically addressed ultracold atoms. To this end, spacially dependent dark states are necessary for the internal states of the atoms. A tripod level scheme yields two degenerate dark states which leads to a non-Abelian SU(2) gauge field. These fields can be understood in terms of spin-orbit coupling between the momentum of the atom and its internal pseudo-spin formed by the dark state manifold. On a ring trap, this spin-orbit coupling leads to internal and spacial Josephson oscillations, persistent currents and grey solitons. The influence of interatomic interactions is crucial for solitons and leads to modifications of the groundstate in a harmonically trapped scenario. Similarities between ultracold atoms and high energy physics are drawn in the low momentum limit as the dispersion relation offers a widely controllable Dirac cone there. With an induced mass gap Zitterbewegung and bright solitons are investigated. Moreover, non-linear Dirac equations, adapted from high energy physics, lead to new self confining solutions for ultracold gases. Further analogues between ultracold atoms and quantum chromodynamics, like chiral symmetry breaking are discussed
Subjects/Keywords: 535
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APA (6th Edition):
Merkl, M. (2010). Schrodinger, Dirac and beyond : non-Abelian gauge fields in ultracold quantum gases. (Doctoral Dissertation). Heriot-Watt University. Retrieved from http://hdl.handle.net/10399/2329
Chicago Manual of Style (16th Edition):
Merkl, Michael. “Schrodinger, Dirac and beyond : non-Abelian gauge fields in ultracold quantum gases.” 2010. Doctoral Dissertation, Heriot-Watt University. Accessed September 21, 2019.
http://hdl.handle.net/10399/2329.
MLA Handbook (7th Edition):
Merkl, Michael. “Schrodinger, Dirac and beyond : non-Abelian gauge fields in ultracold quantum gases.” 2010. Web. 21 Sep 2019.
Vancouver:
Merkl M. Schrodinger, Dirac and beyond : non-Abelian gauge fields in ultracold quantum gases. [Internet] [Doctoral dissertation]. Heriot-Watt University; 2010. [cited 2019 Sep 21].
Available from: http://hdl.handle.net/10399/2329.
Council of Science Editors:
Merkl M. Schrodinger, Dirac and beyond : non-Abelian gauge fields in ultracold quantum gases. [Doctoral Dissertation]. Heriot-Watt University; 2010. Available from: http://hdl.handle.net/10399/2329
Heriot-Watt University
6.
Cuesta Contreras, Angel.
Geometric and photometric affine invariant image registration.
Degree: PhD, 2009, Heriot-Watt University
URL: http://hdl.handle.net/10399/2228
► This thesis aims to present a solution to the correspondence problem for the registration of wide-baseline images taken from uncalibrated cameras. We propose an affine…
(more)
▼ This thesis aims to present a solution to the correspondence problem for the registration of wide-baseline images taken from uncalibrated cameras. We propose an affine invariant descriptor that combines the geometry and photometry of the scene to find correspondences between both views. The geometric affine invariant component of the descriptor is based on the affine arc-length metric, whereas the photometry is analysed by invariant colour moments. A graph structure represents the spatial distribution of the primitive features; i.e. nodes correspond to detected high-curvature points, whereas arcs represent connectivities by extracted contours. After matching, we refine the search for correspondences by using a maximum likelihood robust algorithm. We have evaluated the system over synthetic and real data. The method is endemic to propagation of errors introduced by approximations in the system.
Subjects/Keywords: 535
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APA (6th Edition):
Cuesta Contreras, A. (2009). Geometric and photometric affine invariant image registration. (Doctoral Dissertation). Heriot-Watt University. Retrieved from http://hdl.handle.net/10399/2228
Chicago Manual of Style (16th Edition):
Cuesta Contreras, Angel. “Geometric and photometric affine invariant image registration.” 2009. Doctoral Dissertation, Heriot-Watt University. Accessed September 21, 2019.
http://hdl.handle.net/10399/2228.
MLA Handbook (7th Edition):
Cuesta Contreras, Angel. “Geometric and photometric affine invariant image registration.” 2009. Web. 21 Sep 2019.
Vancouver:
Cuesta Contreras A. Geometric and photometric affine invariant image registration. [Internet] [Doctoral dissertation]. Heriot-Watt University; 2009. [cited 2019 Sep 21].
Available from: http://hdl.handle.net/10399/2228.
Council of Science Editors:
Cuesta Contreras A. Geometric and photometric affine invariant image registration. [Doctoral Dissertation]. Heriot-Watt University; 2009. Available from: http://hdl.handle.net/10399/2228
Heriot-Watt University
7.
Thomson, Ian James.
Efficient, high-power operation of CW Yb:YAG and Q-switched Nd:YAG planar waveguide lasers.
Degree: PhD, 2010, Heriot-Watt University
URL: http://hdl.handle.net/10399/2333
► The planar waveguide gain medium o ers a good approach to creating a high- power lasers. Excellent thermal properties allow for lasers with good beam-quality…
(more)
▼ The planar waveguide gain medium o ers a good approach to creating a high- power lasers. Excellent thermal properties allow for lasers with good beam-quality and high-e ciency. A Neodymium doped YAG planar waveguide laser was actively Q-switched using a hybrid unstable resonator and acousto-optic modulator. A Yt- terbium doped YAG planar waveguide laser was side-pumped using two laser diode stacks with a total of 800 W incident pump power. The Nd:YAG planar waveguide laser has a core 200 um thick and was face pumped with ten laser diode bars. Q-switching was achieved through the use of a new hybrid unstable resonator con guration providing high-speed modulation of the laser cavity. The laser produced 100 W of average power with a pulse repetition rate of 100 kHz, giving 1 mJ pulses with 50 ns duration. Shorter 15 ns pulses were achieved with 4.5 mJ pulse energy at lower pulse repetition rates. The Yb:YAG planar waveguide laser has a 150 um core thickness, side pumped by two 430 W, six-bar diode laser stacks. Each diode stack has a custom phase- plate, correcting for collimation errors and lens aberrations. These gave a line focus matching the dimensions of the waveguide core with an incident intensity on each side of approximately 22 kWcm-2. Ray tracing of spontaneous emission within the waveguide core shows side facet angles of 7 and 20 were required to minimise ASE and parasitic oscillations within the waveguide core. A technique to image the uorescence from the Yb:YAG waveguide core has been developed. This technique allows for easy alignment of the pump lasers to the waveg- uide core and measurement of the pump intensity pro le throughout the planar waveg- uide. This technique showed single-sided pumping to follow Beer's law, and with double-sided pumping considerably improved the pump uniformity. A diode laser probe was used to measure the gain present within the waveguide. The small signal gain coe cient was shown to be 1 cm-1 with a uniform pro le across the width of the waveguide when pumped to saturation. This highlights the potential of operating the planar waveguide laser as an e cient ampli er. High-power high-e ciency operation of the Yb:YAG planar waveguide laser was achieved through the use of a hybrid stable waveguide resonator. Output power of 400 W was extracted in a multi-mode beam with a slope e ciency of 75%. This result represents the highest output power from a diode-pumped solid-state planar waveguide laser to date.
Subjects/Keywords: 535
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APA ·
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APA (6th Edition):
Thomson, I. J. (2010). Efficient, high-power operation of CW Yb:YAG and Q-switched Nd:YAG planar waveguide lasers. (Doctoral Dissertation). Heriot-Watt University. Retrieved from http://hdl.handle.net/10399/2333
Chicago Manual of Style (16th Edition):
Thomson, Ian James. “Efficient, high-power operation of CW Yb:YAG and Q-switched Nd:YAG planar waveguide lasers.” 2010. Doctoral Dissertation, Heriot-Watt University. Accessed September 21, 2019.
http://hdl.handle.net/10399/2333.
MLA Handbook (7th Edition):
Thomson, Ian James. “Efficient, high-power operation of CW Yb:YAG and Q-switched Nd:YAG planar waveguide lasers.” 2010. Web. 21 Sep 2019.
Vancouver:
Thomson IJ. Efficient, high-power operation of CW Yb:YAG and Q-switched Nd:YAG planar waveguide lasers. [Internet] [Doctoral dissertation]. Heriot-Watt University; 2010. [cited 2019 Sep 21].
Available from: http://hdl.handle.net/10399/2333.
Council of Science Editors:
Thomson IJ. Efficient, high-power operation of CW Yb:YAG and Q-switched Nd:YAG planar waveguide lasers. [Doctoral Dissertation]. Heriot-Watt University; 2010. Available from: http://hdl.handle.net/10399/2333
Heriot-Watt University
8.
Hudelist, Florian.
Design and characterisation of nanostructured gradient index lenses.
Degree: PhD, 2010, Heriot-Watt University
URL: http://hdl.handle.net/10399/2355
► The design and characterisation of nanostructured gradient index lenses is investigated in this thesis. Nanostructured gradient index materials achieve their refractive index pro le by…
(more)
▼ The design and characterisation of nanostructured gradient index lenses is investigated in this thesis. Nanostructured gradient index materials achieve their refractive index pro le by creating a pattern with feature sizes of =5 and smaller from two glasses with di erent refractive indices. These structures are fabricated by the stack-anddraw technology generally used for photonic crystal bres. The rigorous theoretical analysis is performed with the Fourier modal method or the nite di erence time domain algorithm. A comprehensive introduction of the Fourier modal method for one and two dimensional gratings is given. Due to the inherit periodicity of the Fourier modal method, an algorithm to calculate the transmitted eld of isolated non-periodic lamellar gratings is developed and tested experimentally with a multi layer lens grating in the microwave regime. Furthermore, the eld stitching method for the analysis of large two dimensional gratings with very small feature sizes is developed. The numerical performance is tested with a di ractive element consisting of 32 32 pixels and shown to reduce the required memory as well as the computation time by more than an order of magnitude in certain con gurations. Considerations of symmetries in the grating structure are also included in the derivation of the eld stitching method. The e ective medium theory for nanostructured gradient index materials is introduced which allows to describe nanostructured materials with the equations for standard gradient index lenses. The stack-and-draw fabrication process is described including the choice of glass types, assembly and drawing of the preforms. For the design of the required binary pattern, the simulated annealing algorithm is used in conjunction with the e ective medium theory. In order to provide experimental evidence of the simulations, two lenses were assembled from PTFE rods with a diameter of 6mm and characterised in the microwave regime at = 3 cm. It is shown that with this wavelength to feature size ratio, the nanostructured gradient index lenses can have properties nearly identical to conventional gradient index lenses. Finally, a spherical and an elliptical nanostructured microlens are characterised in the optical regime. On the elliptical microlens, phase and intensity measurements are performed and compared to simulations obtained with the Fourier modal method.
Subjects/Keywords: 535
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APA (6th Edition):
Hudelist, F. (2010). Design and characterisation of nanostructured gradient index lenses. (Doctoral Dissertation). Heriot-Watt University. Retrieved from http://hdl.handle.net/10399/2355
Chicago Manual of Style (16th Edition):
Hudelist, Florian. “Design and characterisation of nanostructured gradient index lenses.” 2010. Doctoral Dissertation, Heriot-Watt University. Accessed September 21, 2019.
http://hdl.handle.net/10399/2355.
MLA Handbook (7th Edition):
Hudelist, Florian. “Design and characterisation of nanostructured gradient index lenses.” 2010. Web. 21 Sep 2019.
Vancouver:
Hudelist F. Design and characterisation of nanostructured gradient index lenses. [Internet] [Doctoral dissertation]. Heriot-Watt University; 2010. [cited 2019 Sep 21].
Available from: http://hdl.handle.net/10399/2355.
Council of Science Editors:
Hudelist F. Design and characterisation of nanostructured gradient index lenses. [Doctoral Dissertation]. Heriot-Watt University; 2010. Available from: http://hdl.handle.net/10399/2355
Heriot-Watt University
9.
McCracken, Richard A.
Femtosecond optical parametric oscillator frequency combs for coherent pulse synthesis.
Degree: PhD, 2013, Heriot-Watt University
URL: http://hdl.handle.net/10399/2702
► Coherent pulse synthesis takes as its objective the piecewise assembly of a sequence of identical broadband pulses from two or more mutually-coherent sequences of narrowband…
(more)
▼ Coherent pulse synthesis takes as its objective the piecewise assembly of a sequence of identical broadband pulses from two or more mutually-coherent sequences of narrowband pulses. The requirements for pulse synthesis are that the parent pulses share the same repetition frequency, are phase coherent and have low mutual timing jitter over the required observation time. The work carried out in this thesis explored the requirements for broadband coherent pulse synthesis between the multiple visible outputs of a synchronously pumped femtosecond optical parametric oscillator. A femtosecond Ti:sapphire laser was characterised and used to pump a PPKTP-based OPO that produced a number of second-harmonic and sum-frequency mixing outputs across the visible region. Using a novel lock-to-zero CEO stabilisation technique, broadband phase coherence was established between all the pulses on the optical bench, producing the broadest zero-offset frequency comb to date. Employing a common optical path for all the pulses provided common-mode rejection of noise, ensuring less than 150 attoseconds of timing jitter between the pulses over a 1 second observation window. The parent pulses were compressed and their relative delays altered in a quasi-common path prism delay line, allowing pulse synthesis at a desired reference plane.
Subjects/Keywords: 535
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APA (6th Edition):
McCracken, R. A. (2013). Femtosecond optical parametric oscillator frequency combs for coherent pulse synthesis. (Doctoral Dissertation). Heriot-Watt University. Retrieved from http://hdl.handle.net/10399/2702
Chicago Manual of Style (16th Edition):
McCracken, Richard A. “Femtosecond optical parametric oscillator frequency combs for coherent pulse synthesis.” 2013. Doctoral Dissertation, Heriot-Watt University. Accessed September 21, 2019.
http://hdl.handle.net/10399/2702.
MLA Handbook (7th Edition):
McCracken, Richard A. “Femtosecond optical parametric oscillator frequency combs for coherent pulse synthesis.” 2013. Web. 21 Sep 2019.
Vancouver:
McCracken RA. Femtosecond optical parametric oscillator frequency combs for coherent pulse synthesis. [Internet] [Doctoral dissertation]. Heriot-Watt University; 2013. [cited 2019 Sep 21].
Available from: http://hdl.handle.net/10399/2702.
Council of Science Editors:
McCracken RA. Femtosecond optical parametric oscillator frequency combs for coherent pulse synthesis. [Doctoral Dissertation]. Heriot-Watt University; 2013. Available from: http://hdl.handle.net/10399/2702
10.
Hawkins, Peter.
High harmonic generation in periodic systems.
Degree: PhD, 2016, Imperial College London
URL: http://hdl.handle.net/10044/1/43375
► In this thesis theoretical models for describing ultrafast dynamics and High Harmonic Generation (HHG) in bulk periodic systems are developed. HHG in bulk solid state…
(more)
▼ In this thesis theoretical models for describing ultrafast dynamics and High Harmonic Generation (HHG) in bulk periodic systems are developed. HHG in bulk solid state systems has been achieved by several groups over the last few years. In this thesis a review of recent results is presented, with attention paid to the development of theoretical models for the HHG process in periodic solids. A closed form expression for a Landau-Dykhne type sub-cycle transition rate between bands of nearest-neighbour tight-binding structures is derived. This rate is used to construct a semi-classical model for HHG in solids. The sub-cycle nature of the transition rate is shown to lead to destructive interference of currents in the conduction band. The time dependent Schödinger equation is employed in the accelerated Bloch basis to study the effect of multiple bands on the HHG process. For mid-IR fields transitions between bands can be sufficiently strong that transitions between the conduction bands suppress the Bragg reflection process. It is shown that such transitions can form an effective nearly parabolic conduction band, and lead to a large reduction in harmonic intensity compared to single conduction band models. The prediction of destructive interference of current in the conduction band of periodic solids is studied in ZnO, using a non-local empirical pseudopotential band structure and matrix elements, in the density matrix formalism, with the inclusion of dephasing effects. It is shown that the quantum destructive interference is present in the density matrix calculation, closely matching semi-classical predictions. The effect of multiple bands of the structure, and variation in the dephasing timescale of the system is also considered.
Subjects/Keywords: 535
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APA (6th Edition):
Hawkins, P. (2016). High harmonic generation in periodic systems. (Doctoral Dissertation). Imperial College London. Retrieved from http://hdl.handle.net/10044/1/43375
Chicago Manual of Style (16th Edition):
Hawkins, Peter. “High harmonic generation in periodic systems.” 2016. Doctoral Dissertation, Imperial College London. Accessed September 21, 2019.
http://hdl.handle.net/10044/1/43375.
MLA Handbook (7th Edition):
Hawkins, Peter. “High harmonic generation in periodic systems.” 2016. Web. 21 Sep 2019.
Vancouver:
Hawkins P. High harmonic generation in periodic systems. [Internet] [Doctoral dissertation]. Imperial College London; 2016. [cited 2019 Sep 21].
Available from: http://hdl.handle.net/10044/1/43375.
Council of Science Editors:
Hawkins P. High harmonic generation in periodic systems. [Doctoral Dissertation]. Imperial College London; 2016. Available from: http://hdl.handle.net/10044/1/43375
Durham University
11.
Lemke, Ulrike.
Measurement uncertainties in fibre-coupled spectrographs.
Degree: PhD, 2012, Durham University
URL: http://etheses.dur.ac.uk/3412/
;
http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.548837
► The signal quality of fibre-coupled spectrographs can be limited by the inherent properties of the optical fibre. This is especially the case for applications that…
(more)
▼ The signal quality of fibre-coupled spectrographs can be limited by the inherent properties of the optical fibre. This is especially the case for applications that require high signal-to-noise performance and high spectral resolution. Examples include metallicity and age of star clusters, as well as investigations of Lyman-alpha absorbers. Extra-solar planet research in particular encounters its limitations due to the non-repeatability of the fibre response. Initially, a limited signal quality due to fibres seems counter-intuitive, since one of the most remarkable advantages of fibres is their signal stabilizing property, called image scrambling, which refers to the effect that the fibre output signal is largely insensitive to variations at the input side. However, the fibre photometric and barycentre response is sub ject to external parameters like stress, seeing and guiding variations. State-of-the-art instrumentation has attained a level of sensitivity where these effects will impact upon instrument performance, especially when advancing to a regime of spectral resolving powers where the quantized character of the standard optical fibre can be resolved, which manifests itself in modal noise. Unprecedented effort will be required in order to accomplish high resolving powers in the spectral and spatial domains with 40 m class telescopes. It is therefore essential to predict these fibre-related measurement uncertainties so that the performance of current and future instruments can be optimized. This thesis starts out with a phenomenological description of the different effects that give rise to fibre-related noise and its influence on the observables relevant to astrophysics, such as barycentre and photometric stability. Special emphasis is given to the photometric uncertainties related to modal noise, where first a theoretical model is outlined which in later chapters will be sub ject to experimental investigations. Subsequently, the barycentre repeatability due to incomplete scrambling is the subject of detailed investigation. The remaining sources of noise are estimated using experimental data as well as simulations and put in contrast with the other effects. Alongside the quantitative prediction of instrument instabilities, mitigation strategies will be presented and discussed. I conclude with a brief discussion of the impact of incomplete scrambling and modal noise on current instrumentation, the implications for future instrument pro jects as well as future work that will help to further understand and obviate the underlying mechanisms.
Subjects/Keywords: 535
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APA (6th Edition):
Lemke, U. (2012). Measurement uncertainties in fibre-coupled spectrographs. (Doctoral Dissertation). Durham University. Retrieved from http://etheses.dur.ac.uk/3412/ ; http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.548837
Chicago Manual of Style (16th Edition):
Lemke, Ulrike. “Measurement uncertainties in fibre-coupled spectrographs.” 2012. Doctoral Dissertation, Durham University. Accessed September 21, 2019.
http://etheses.dur.ac.uk/3412/ ; http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.548837.
MLA Handbook (7th Edition):
Lemke, Ulrike. “Measurement uncertainties in fibre-coupled spectrographs.” 2012. Web. 21 Sep 2019.
Vancouver:
Lemke U. Measurement uncertainties in fibre-coupled spectrographs. [Internet] [Doctoral dissertation]. Durham University; 2012. [cited 2019 Sep 21].
Available from: http://etheses.dur.ac.uk/3412/ ; http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.548837.
Council of Science Editors:
Lemke U. Measurement uncertainties in fibre-coupled spectrographs. [Doctoral Dissertation]. Durham University; 2012. Available from: http://etheses.dur.ac.uk/3412/ ; http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.548837
Durham University
12.
Tanasittikosol, Monsit.
Rydberg dark states in external fields.
Degree: PhD, 2011, Durham University
URL: http://etheses.dur.ac.uk/3287/
;
http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.545422
► We initially discuss the theory of three-level systems using the dressed state formalism. One of the dressed states, containing a ground state and a Rydberg…
(more)
▼ We initially discuss the theory of three-level systems using the dressed state formalism. One of the dressed states, containing a ground state and a Rydberg state, does not couple with the probe laser; thus, the medium becomes transparent to the latter. This phenomenon is known as electro- magnetically induced transparency (EIT) and this dressed state is known as a Rydberg dark state. We show that EIT can be used to extract the reduced dipole matrix element for transitions to a Rydberg state. However, a prob- lem with three-level Rydberg EIT in a vapour cell is the occurrence of space charges caused by photoelectric ionisation of Rb metal deposited inside the cell. To avoid this problem, we consider adding a third laser resonant with a fourth level. This is to avoid using the laser whose wavelength is less than the threshold wavelength. In cold atoms, the effect of the third laser is to split the usual EIT resonance into a doublet. In thermal atoms, we observe narrow features due to electromagnetically induced absorption and electro- magnetically induced transparency in the Doppler-free configuration. Next we consider the action of a far off-resonance radio frequency (rf) field in the three-level system. We demonstrate the formation of rf-dressed EIT reso- nances in a thermal Rb vapour and show that such states exhibit enhanced sensitivity to dc electric fields compared to their bare counterparts. Fitting the corresponding EIT profile enables precise measurements of the dc field in- dependent of laser frequency fluctuations. We further investigate the theory of rf-dressed Rydberg EIT using the Floquet approach in order to understand the formation of the sideband structure of the Rydberg state. We find that if the time scale of the rf interaction is much shorter than that of the system evolution and decoherence, the sideband structure is well resolved. We also show that the intermediate state exhibits a sideband structure, induced by the Rydberg state, when the Rabi frequency of coupling laser is larger than twice the modulation frequency. Finally we consider resonant microwave cou- pling between the Rydberg states which leads to an Autler-Townes splitting of the EIT resonance in cold atoms. This splitting can be employed to vary the group index by ±105 allowing independent control of the absorptive and dispersive properties of the medium, i.e., one can switch the transparency of the medium or control the group velocity of a pulse propagation by tuning on and off the microwave field.
Subjects/Keywords: 535
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APA (6th Edition):
Tanasittikosol, M. (2011). Rydberg dark states in external fields. (Doctoral Dissertation). Durham University. Retrieved from http://etheses.dur.ac.uk/3287/ ; http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.545422
Chicago Manual of Style (16th Edition):
Tanasittikosol, Monsit. “Rydberg dark states in external fields.” 2011. Doctoral Dissertation, Durham University. Accessed September 21, 2019.
http://etheses.dur.ac.uk/3287/ ; http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.545422.
MLA Handbook (7th Edition):
Tanasittikosol, Monsit. “Rydberg dark states in external fields.” 2011. Web. 21 Sep 2019.
Vancouver:
Tanasittikosol M. Rydberg dark states in external fields. [Internet] [Doctoral dissertation]. Durham University; 2011. [cited 2019 Sep 21].
Available from: http://etheses.dur.ac.uk/3287/ ; http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.545422.
Council of Science Editors:
Tanasittikosol M. Rydberg dark states in external fields. [Doctoral Dissertation]. Durham University; 2011. Available from: http://etheses.dur.ac.uk/3287/ ; http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.545422
13.
Lee, Chee-Leong.
Micro-scale processing of diamond structures and devices.
Degree: PhD, 2008, University of Strathclyde
URL: http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=26099
;
http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.510674
► In this project, Inductively Coupled Plasma (ICP) etching of natural and synthetic diamond using oxygen-based (Ar/0₂) and chlorine-based (Ar/Cl₂) plasmas was investigated. The effects of…
(more)
▼ In this project, Inductively Coupled Plasma (ICP) etching of natural and synthetic diamond using oxygen-based (Ar/0₂) and chlorine-based (Ar/Cl₂) plasmas was investigated. The effects of ICP platen and coil powers and gas pressures on the diamond etching were also studied. It was demonstrated that the diamond etch rate and etch selectivity using Ar/Cl₂ plasma etching, with high etch controllability (on the nanometre scale) and capabilities of removing the sub-surface damage and improving the surface smoothness, is only half of those by using Ar/0₂ plasma. Based on these studies, various diamond micro-optics including diamond microspherical positive and negative lenses, micro-cylindrical and micro-ring lenses, complex micro-lenses and optical gratings were designed and successfully fabricated. Structural and optical characterisations revealed the high optical quality and functionality of the fabricated diamond micro-optics. Applications of diamond micro-optics, such as micro-lensed micro-VECSEL photonic devices were also demonstrated. Utilising ICP Ar/Ch plasma etching and other processes, prototype diamond electronic devices such as diamond MISFETs and MOSFETs have been fabricated. To realize such diamond FET devices, ohmic contacts with low specific contact resistances, which can be achieved by applying aqua regia surface treatment and laser ablation techniques on the p-doped diamond, are imperative. However, it was found that the gate leakage currents of the diamond MISFET devices were quite large due to leakage through the diamond intrinsic layer under the gate. To overcome this problem, diamond MOSFET devices employing Si0₂ as gate insulation material were developed, which were able to sustain large gate biases with very low leakage currents. However, these diamond MOSFET devices could not be fully pinched-off which may be due to the high boron concentration and relatively thick delta layer, which leads to excessive charge in the channel of the device. By fabricating a recess gate diamond p-MOSFET, gate field control was much enhanced.
Subjects/Keywords: 535
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APA (6th Edition):
Lee, C. (2008). Micro-scale processing of diamond structures and devices. (Doctoral Dissertation). University of Strathclyde. Retrieved from http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=26099 ; http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.510674
Chicago Manual of Style (16th Edition):
Lee, Chee-Leong. “Micro-scale processing of diamond structures and devices.” 2008. Doctoral Dissertation, University of Strathclyde. Accessed September 21, 2019.
http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=26099 ; http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.510674.
MLA Handbook (7th Edition):
Lee, Chee-Leong. “Micro-scale processing of diamond structures and devices.” 2008. Web. 21 Sep 2019.
Vancouver:
Lee C. Micro-scale processing of diamond structures and devices. [Internet] [Doctoral dissertation]. University of Strathclyde; 2008. [cited 2019 Sep 21].
Available from: http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=26099 ; http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.510674.
Council of Science Editors:
Lee C. Micro-scale processing of diamond structures and devices. [Doctoral Dissertation]. University of Strathclyde; 2008. Available from: http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=26099 ; http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.510674
Cranfield University
14.
Topliss, Stephen M.
Optical fibre long period grating sensors with nanostructured coatings.
Degree: PhD, 2011, Cranfield University
URL: http://dspace.lib.cranfield.ac.uk/handle/1826/6799
;
http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.542230
► The dual resonant response of long period fibre gratings (LPG) operating near the phase matching turning point to the deposition of nanostructured coatings is explored.…
(more)
▼ The dual resonant response of long period fibre gratings (LPG) operating near the phase matching turning point to the deposition of nanostructured coatings is explored. A broad range of LPGs have been fabricated with grating periods ranging from 80m to 180m, and these have been characterized with three different coating materials,-tricosensoic acid, undecyl-calix[4]resorcarene and tert-butyl-calix[8]arene carboxylic acid. The dual resonant response has been exploited with the construction of an LPG based sensor coated with a quinolinium dye forming a pH sensor. The wavelength response of this device was measured with a sensitivity of -0.55pH/nm. Furthermore, length apodised phase shifted long period gratings have been characterized, and the effect on the dual resonant response has been recorded. Partial coating of this device has resulted in the observation of a bandgap feature in the wavelength response. The use of calixarenes as a functional coating for long period fibre gratings is also investigated. Calixarene is applied in a thin layer with a thickness of several hundred nm’s to the cladding of the fibre in the region containing the LPG sensor. The chemical sensing capabilities of a long period fibre grating sensor is presented for the detection of the volatile organic compounds; hexane, cyclohexane, benzene and toluene. The wavelength response was measured and the sensitivity to toluene vapour was recorded at 1600ppmv/nm. Using intensity detection of the central maxima in the wavelength response, the chemical selectivity is demonstrated showing sensitivity to toluene vapour over 13 times greater compared to hexane vapour.
Subjects/Keywords: 535
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APA (6th Edition):
Topliss, S. M. (2011). Optical fibre long period grating sensors with nanostructured coatings. (Doctoral Dissertation). Cranfield University. Retrieved from http://dspace.lib.cranfield.ac.uk/handle/1826/6799 ; http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.542230
Chicago Manual of Style (16th Edition):
Topliss, Stephen M. “Optical fibre long period grating sensors with nanostructured coatings.” 2011. Doctoral Dissertation, Cranfield University. Accessed September 21, 2019.
http://dspace.lib.cranfield.ac.uk/handle/1826/6799 ; http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.542230.
MLA Handbook (7th Edition):
Topliss, Stephen M. “Optical fibre long period grating sensors with nanostructured coatings.” 2011. Web. 21 Sep 2019.
Vancouver:
Topliss SM. Optical fibre long period grating sensors with nanostructured coatings. [Internet] [Doctoral dissertation]. Cranfield University; 2011. [cited 2019 Sep 21].
Available from: http://dspace.lib.cranfield.ac.uk/handle/1826/6799 ; http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.542230.
Council of Science Editors:
Topliss SM. Optical fibre long period grating sensors with nanostructured coatings. [Doctoral Dissertation]. Cranfield University; 2011. Available from: http://dspace.lib.cranfield.ac.uk/handle/1826/6799 ; http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.542230
University of York
15.
Wilson, Lucy.
Extreme ultraviolet probing of laser irradiated solid targets.
Degree: PhD, 2013, University of York
URL: http://etheses.whiterose.ac.uk/4336/
;
http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.581630
► This thesis explores the applications of extreme ultra-violet (EUV) radiation to the probing of plasma materials and the importance of extreme ultra-violet radiation in radiative…
(more)
▼ This thesis explores the applications of extreme ultra-violet (EUV) radiation to the probing of plasma materials and the importance of extreme ultra-violet radiation in radiative transfer in plasmas relevant to both ICF and astrophysics. The complex refractive index of solid aluminium and the imaginary part of the refractive index of solid iron between 17 eV and 39 eV have been measured using EUV harmonics produced from an 800nm laser focused to 1014Wcm-2 in an argon gas jet impinging on a double slit interferometer. There is potential for further work with this method to measure the complex refractive index of plasma material. It is shown that the drop in opacity when bound-free photo-ionization is no longer energetically possible, enables measurements of the transmission of extreme ultra-violet (EUV) laser pulses at 13.9 nm to act as a signature of the heating of thin (50 nm) iron layers with 50 nm thick parylene-N (CH) overlay irradiated by 35 fs pulses at an irradiance of 3x�1016 Wcm-2. Comparing EUV transmission measurements at different times after irradiation to fluid code simulations shows that the target is instantaneously heated by hot electrons (with approximately 10% of the laser energy),followed by thermal conduction. The diagnostic potential of extreme ultraviolet (EUV) coherent probing within a laser produced plasma with a simple transmission footprint is investigated. A fluid code is used to model the interaction of a 35fs, 2�x10-14Wcm2 800nm laser pulse with an 800nm thick aluminium target. A post processor is used to calculate the target’s refractive index and transmission to 45eV radiation. The effects of EUV radial phase variations at the rear of the target on the intensity distribution at a detector 1.5m from the target are studied. An irradiated aluminium target is found to have little effect on the transmission of 45eV radiation. However, there can be significant phase differences in the probing beam in the radial direction due to heating beam footprint variations for example due to a non-uniform focal spot. These phase variations affect the subsequent propagation of the radiation, suggesting a simple diagnostic measuring the far-field footprint of coherent EUV radiation passing through an irradiated target is sensitive to radial variations of the target heating.
Subjects/Keywords: 535
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APA (6th Edition):
Wilson, L. (2013). Extreme ultraviolet probing of laser irradiated solid targets. (Doctoral Dissertation). University of York. Retrieved from http://etheses.whiterose.ac.uk/4336/ ; http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.581630
Chicago Manual of Style (16th Edition):
Wilson, Lucy. “Extreme ultraviolet probing of laser irradiated solid targets.” 2013. Doctoral Dissertation, University of York. Accessed September 21, 2019.
http://etheses.whiterose.ac.uk/4336/ ; http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.581630.
MLA Handbook (7th Edition):
Wilson, Lucy. “Extreme ultraviolet probing of laser irradiated solid targets.” 2013. Web. 21 Sep 2019.
Vancouver:
Wilson L. Extreme ultraviolet probing of laser irradiated solid targets. [Internet] [Doctoral dissertation]. University of York; 2013. [cited 2019 Sep 21].
Available from: http://etheses.whiterose.ac.uk/4336/ ; http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.581630.
Council of Science Editors:
Wilson L. Extreme ultraviolet probing of laser irradiated solid targets. [Doctoral Dissertation]. University of York; 2013. Available from: http://etheses.whiterose.ac.uk/4336/ ; http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.581630
16.
Chaudhary, Mohammad Yaqub.
Charge transport, injection and optical properties of fluorene based copolymers.
Degree: PhD, 2015, Imperial College London
URL: http://hdl.handle.net/10044/1/33205
► In this work we investigate the charge transport, injection and optical properties of several series of fluorene based copolymers. These properties are key areas for…
(more)
▼ In this work we investigate the charge transport, injection and optical properties of several series of fluorene based copolymers. These properties are key areas for polymer semiconductor research studies that are intended to address the challenges of achieving electrically pumped polymer lasing. In general, high charge carrier mobility and luminescence efficiency have been found to be mutually exclusive, however, optimising both together, as well as demonstrating high optical gain will be a significant step to offset losses associated with the mechanisms for lasing. A further requirement is that it is necessary to achieve efficient charge injection in the particular materials that are found to have both of these properties optimised. We concentrate our investigation on fluorene-based copolymers, which have been amongst the earliest classes of materials of interest for polymer lasers (including studies in optically pumped polymer lasers), and since it has previously been shown that high hole mobility and luminescence efficiency may be achieved in fluorene based copolymers with simple alterations to side chain configurations. However, ohmic hole injection into poly(9,9-dioctylfluorene) (PFO) has been difficult to achieve because of its deep-lying highest occupied molecular orbital (HOMO) level of ~5.8eV below the vacuum level. Therefore, in our first experimental study, we revisit the charge transport properties of PFO based on recent developments in the use of transition metal oxides as hole injecting electrodes. With the ability to achieve ohmic injection in PFO, we are able to use Dark Injection Space Charge Limited Current (DI-SCLC) and field effect transistor (FET) techniques, both of which require ohmic injecton for charge transport measurements, and make comparisons with measurements from Time-of-Flight (ToF) photocurrent experiments. Together, these techniques span several orders of magnitude in charge carrier density, which provides an additional perspective on charge transport and the presence of charge traps. The subsequent chapters introduce three series of fluorene-based copolymers. The first series of blue emitting polymers has a resemblance to familiar fluorene based polymers with hexyloxyphenyl substituents instead of linear alkyl side chains and the series contains copolymers with a phenoxazine (BPPX) unit derived from more familiar triarylamine structures. Optical measurements show these polymers are free of morphologies such as the beta-phase and we obtain a hole mobility of ~10-3 cm2/Vs, photoluminescence quantum efficiency (PLQE) of 65.7% and optical gain of 41cm-1 for poly(9,9-di(4-hexyloxyphenyl)fluorene). Transient DI-SCLC measurements are used to show differences in charge trapping behaviour in the series. The final chapter of experimental results is based on novel poly(indenofluorene-fluorene) and poly(indenopyrazine-fluorene) copolymers. In the poly(indenofluorene-fluorene) series we consider the role of increased backbone rigidity compared to polyfluorene and the variation of side chain…
Subjects/Keywords: 535
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Export
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APA (6th Edition):
Chaudhary, M. Y. (2015). Charge transport, injection and optical properties of fluorene based copolymers. (Doctoral Dissertation). Imperial College London. Retrieved from http://hdl.handle.net/10044/1/33205
Chicago Manual of Style (16th Edition):
Chaudhary, Mohammad Yaqub. “Charge transport, injection and optical properties of fluorene based copolymers.” 2015. Doctoral Dissertation, Imperial College London. Accessed September 21, 2019.
http://hdl.handle.net/10044/1/33205.
MLA Handbook (7th Edition):
Chaudhary, Mohammad Yaqub. “Charge transport, injection and optical properties of fluorene based copolymers.” 2015. Web. 21 Sep 2019.
Vancouver:
Chaudhary MY. Charge transport, injection and optical properties of fluorene based copolymers. [Internet] [Doctoral dissertation]. Imperial College London; 2015. [cited 2019 Sep 21].
Available from: http://hdl.handle.net/10044/1/33205.
Council of Science Editors:
Chaudhary MY. Charge transport, injection and optical properties of fluorene based copolymers. [Doctoral Dissertation]. Imperial College London; 2015. Available from: http://hdl.handle.net/10044/1/33205
17.
Iles-Smith, Jake.
Excitation dynamics of strongly dissipative quantum systems.
Degree: PhD, 2015, Imperial College London
URL: http://hdl.handle.net/10044/1/33203
► Strong coupling between a quantum system and its many-body environment is becoming an increasingly important topic for many branches of physics. Numerous systems of experimental…
(more)
▼ Strong coupling between a quantum system and its many-body environment is becoming an increasingly important topic for many branches of physics. Numerous systems of experimental and technological relevance demonstrate strong system-environment coupling, leading to complex dynamical behaviour. This thesis is concerned with two particular examples of such systems, namely quantum dots (QDs) and excitonic energy transfer (EET) in molecular systems. Traditional quantum optics treatments are often insufficient to describe the transient, steady state, and optical properties of QDs due to system-environment correlations. In contrast, we present a modified theory of quantum optics capable of capturing the influence of a thermal environment on the behaviour of QDs. Using this framework we demonstrate a striking departure of the emission spectra and photon measurement statistics of a classically driven QD when compared to an analogous atomic system. Furthermore, in contradiction to accepted notions of decoherence and dissipation, we show that the interaction between a QD and its thermal environment induces non-classical light-matter correlations in an otherwise semi-classical regime of cavity quantum electrodynamics. Away from QDs, we develop the reaction coordinate (RC) formalism to describe the dynamics of a system coupled to a low frequency environment - a regime important to EET systems. We do so by identifying and incorporating important environmental degrees of freedom into an enlarged system Hamiltonian. Uniquely, this approach gives insight directly into the dynamical evolution of the environment and correlations accumulated between the system and environment. Furthermore, it is demonstrated that these corre- lations persist into the steady state, generating non-canonical equilibrium states of the system and environment. We then apply the RC model to describe EET in a molecular dimer, highlighting the effect that under- and over-damped environments have on the excitation dynamics. In doing so, we show interactions between the dimer and a structured environment can significantly enhance the energy transfer rate.
Subjects/Keywords: 535
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APA (6th Edition):
Iles-Smith, J. (2015). Excitation dynamics of strongly dissipative quantum systems. (Doctoral Dissertation). Imperial College London. Retrieved from http://hdl.handle.net/10044/1/33203
Chicago Manual of Style (16th Edition):
Iles-Smith, Jake. “Excitation dynamics of strongly dissipative quantum systems.” 2015. Doctoral Dissertation, Imperial College London. Accessed September 21, 2019.
http://hdl.handle.net/10044/1/33203.
MLA Handbook (7th Edition):
Iles-Smith, Jake. “Excitation dynamics of strongly dissipative quantum systems.” 2015. Web. 21 Sep 2019.
Vancouver:
Iles-Smith J. Excitation dynamics of strongly dissipative quantum systems. [Internet] [Doctoral dissertation]. Imperial College London; 2015. [cited 2019 Sep 21].
Available from: http://hdl.handle.net/10044/1/33203.
Council of Science Editors:
Iles-Smith J. Excitation dynamics of strongly dissipative quantum systems. [Doctoral Dissertation]. Imperial College London; 2015. Available from: http://hdl.handle.net/10044/1/33203
18.
Wee, Wei Hsiung.
The physics of negative refraction and transformation optics.
Degree: PhD, 2011, Imperial College London
URL: http://hdl.handle.net/10044/1/8996
► Whilst optics is one of the oldest field in science, there are still aspects of electromagnetism that we are only beginning to uncover. For instance,…
(more)
▼ Whilst optics is one of the oldest field in science, there are still aspects of electromagnetism that we are only beginning to uncover. For instance, it was demonstrated that materials with simultaneously negative permittivity and permeability exhibit certain exotic behavior; where familiar physical phenomena, such as refraction, are reversed. As such, these materials came to be known as negative refractive index materials (NRIM) and their collective properties as negative refraction. One of the most important and remarkable property of NRIM is perfect lensing - the ability to transport both supra and sub-wavelength optical information from one surface (object plane) to another (image plane), forming images with unprecedented resolution, beyond the diffraction limit. Perfect lensing itself is a consequence of deeper symmetries in electromagnetism, encapsulated in the language of transformation optics - with which we have both a descriptive tool to unify diverse electromagnetic configuarations, as well as a prescriptive tool to design media which bends light at will. While, such transformation medium and NRIM have been demonstrably realised using metamaterials, several challenges remain, of which loss is the major challenge. It is therefore under this trinity of concepts: metamaterials, negative refraction and transformation optics that this thesis is presented. In particular, this thesis illustrates the convergence of the later two concepts, giving rise to a novel class of perfect lens - the compact perfect lens. Here, we shall investigate, their unique properties, construction, challenges, and the dynamics of these lenses. In particular the formulation to study dynamics and effects of losses, is universal; applicable to lenses of any geometry. Finally we shall also propose an alternative universal, top-down approach to overcome losses in perfect lenses using phase conjugation, and demonstrate the capacity of such lenses to see through lossy, translucent obstacles.
Subjects/Keywords: 535
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APA (6th Edition):
Wee, W. H. (2011). The physics of negative refraction and transformation optics. (Doctoral Dissertation). Imperial College London. Retrieved from http://hdl.handle.net/10044/1/8996
Chicago Manual of Style (16th Edition):
Wee, Wei Hsiung. “The physics of negative refraction and transformation optics.” 2011. Doctoral Dissertation, Imperial College London. Accessed September 21, 2019.
http://hdl.handle.net/10044/1/8996.
MLA Handbook (7th Edition):
Wee, Wei Hsiung. “The physics of negative refraction and transformation optics.” 2011. Web. 21 Sep 2019.
Vancouver:
Wee WH. The physics of negative refraction and transformation optics. [Internet] [Doctoral dissertation]. Imperial College London; 2011. [cited 2019 Sep 21].
Available from: http://hdl.handle.net/10044/1/8996.
Council of Science Editors:
Wee WH. The physics of negative refraction and transformation optics. [Doctoral Dissertation]. Imperial College London; 2011. Available from: http://hdl.handle.net/10044/1/8996
19.
Lei, Dang-Yuan.
Superfocusing, biosensing and modulation in plasmonics.
Degree: PhD, 2011, Imperial College London
URL: http://hdl.handle.net/10044/1/9046
► Plasmonics could bridge the gap between photonics and electronics at the nanoscale, by allowing the realization of surface-plasmon-based circuits and plasmonic chips in the future.…
(more)
▼ Plasmonics could bridge the gap between photonics and electronics at the nanoscale, by allowing the realization of surface-plasmon-based circuits and plasmonic chips in the future. To build up such devices, elementary components are required, such as a passive plasmonic lens to focus free-space light to nanometre area and an active plasmonic modulator or switch to control an optical response with an external signal (optical, thermal or electrical). This thesis partially focuses on designing novel passive and active plasmonic devices, with a specific emphasis on the understanding of the physical principles lying behind these nanoscale optical phenomena. Three passive plasmonic devices, designed by conformal transformation optics, are numerically studied, including nanocrescents, kissing and overlapping nanowire dimers. Contrary to conventional metal nanoparticles with just a few resonances, these devices with structural singularities are able to harvest light over a broadband spectrum and focus it into well-defined positions, with potential applications in high efficiency solar cells and nanowire-based photodetectors and nanolasers. Moreover, thermo-optical and electrooptical modulation of plasmon resonances are realized in metallic nanostructures integrated with either a temperature-controlled phase transition material (vanadium dioxide, VO2), or ferroelectric thin films. Taking advantage of the high sensitivity of particle plasmon resonances to the change of its surrounding environment, we develop a plasmon resonance nanospectroscopy technique to study the effects of sizes and defects in the metal-insulator phase transition of VO2 at the single-particle level, and even single-domain level. Finally, we propose and examine the use of two-dimensional metallic nanohole arrays as a refractive index sensing platform for future label-free biosensors with good surface sensitivity and high-throughput detection ability. The designed plasmonic devices have great potential implications for constructing nextgeneration optical computers and chip-scale biosensors. The developed plasmon resonance nanospectroscopy has the potential to probe the interfacial or domain boundary scattering in polycrystalline and epitaxial thin films.
Subjects/Keywords: 535
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APA (6th Edition):
Lei, D. (2011). Superfocusing, biosensing and modulation in plasmonics. (Doctoral Dissertation). Imperial College London. Retrieved from http://hdl.handle.net/10044/1/9046
Chicago Manual of Style (16th Edition):
Lei, Dang-Yuan. “Superfocusing, biosensing and modulation in plasmonics.” 2011. Doctoral Dissertation, Imperial College London. Accessed September 21, 2019.
http://hdl.handle.net/10044/1/9046.
MLA Handbook (7th Edition):
Lei, Dang-Yuan. “Superfocusing, biosensing and modulation in plasmonics.” 2011. Web. 21 Sep 2019.
Vancouver:
Lei D. Superfocusing, biosensing and modulation in plasmonics. [Internet] [Doctoral dissertation]. Imperial College London; 2011. [cited 2019 Sep 21].
Available from: http://hdl.handle.net/10044/1/9046.
Council of Science Editors:
Lei D. Superfocusing, biosensing and modulation in plasmonics. [Doctoral Dissertation]. Imperial College London; 2011. Available from: http://hdl.handle.net/10044/1/9046
20.
Norfolk, Andrew W. G.
Bessel beams : a novel approach to periodic structures.
Degree: PhD, 2010, Imperial College London
URL: http://hdl.handle.net/10044/1/6035
► Bessel and Bessel-like beams in Kerr-like nonlinear materials are numerically investigated. This is conducted with a view to exploiting the behaviour of such profiles for…
(more)
▼ Bessel and Bessel-like beams in Kerr-like nonlinear materials are numerically investigated. This is conducted with a view to exploiting the behaviour of such profiles for the direct laser writing of periodic structures in highly nonlinear glasses. A highly efficient numerical model is developed for the propagation of radially symmetric profiles based on the quasi-discrete Hankel transform (QDHT), making use of a reconstruction relation to allow the field to be sampled at arbitrary positions that do not coincide with the numerical grid. This Hankel-based Adaptive Radial Propagator (HARP) is shown to be up to 1000 times faster than standard FFT-based methods. The critical self-focusing of the Gaussian beam is reproduced to confirm the accuracy of HARP. Following this the critical self-focusing behaviour of a Bessel-Gauss beam is investigated. It is observed that, for certain parameters, increasing the beam power may prevent blowup in the Bessel-Gauss beam. Below the threshold for self-focusing the Bessel-Gauss beam exhibits periodic modulation in the direction of propagation. The existing equation describing this behaviour is shown to be inaccurate and a modification is proposed based on a power dependent beat-length. This modified beat-length equation is demonstrated to be accurate in both the paraxial and quasi-nonparaxial regime. As the beam decays, the intensity modulation appears negatively chirped. It is demonstrated that this chirp may be controlled through careful shaping of the window. It is also shown that a small Gaussian seed beam may be used to control the positions of the maxima. It is demonstrated that a set of nonlinear Bessel functions exist that exhibit a similar quasi-stationary behaviour in a nonlinear medium to the linear Bessel beam in a linear medium. Furthermore it is shown for the first time that higher-order, Bessel-like, stationary solutions exist for beams with azimuthal phase, and boundary conditions for these functions are derived.
Subjects/Keywords: 535
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APA (6th Edition):
Norfolk, A. W. G. (2010). Bessel beams : a novel approach to periodic structures. (Doctoral Dissertation). Imperial College London. Retrieved from http://hdl.handle.net/10044/1/6035
Chicago Manual of Style (16th Edition):
Norfolk, Andrew W G. “Bessel beams : a novel approach to periodic structures.” 2010. Doctoral Dissertation, Imperial College London. Accessed September 21, 2019.
http://hdl.handle.net/10044/1/6035.
MLA Handbook (7th Edition):
Norfolk, Andrew W G. “Bessel beams : a novel approach to periodic structures.” 2010. Web. 21 Sep 2019.
Vancouver:
Norfolk AWG. Bessel beams : a novel approach to periodic structures. [Internet] [Doctoral dissertation]. Imperial College London; 2010. [cited 2019 Sep 21].
Available from: http://hdl.handle.net/10044/1/6035.
Council of Science Editors:
Norfolk AWG. Bessel beams : a novel approach to periodic structures. [Doctoral Dissertation]. Imperial College London; 2010. Available from: http://hdl.handle.net/10044/1/6035
21.
Bissell, John Joseph.
Magnetised transport and instability in laser produced plasmas.
Degree: PhD, 2012, Imperial College London
URL: http://hdl.handle.net/10044/1/9176
► Classical transport theory predicts strong coupling between thermal transport and magnetic field dynamics in laser produced plasmas; for example, fields are carried with the thermal…
(more)
▼ Classical transport theory predicts strong coupling between thermal transport and magnetic field dynamics in laser produced plasmas; for example, fields are carried with the thermal flux, via the Nernst effect, while simultaneously deflecting it, giving rise to a Righi-Leduc heat-flow. Coupling between these effects is shown here to drive a new kind of instability-the magnetothermal instability-which is described in detail for the first time. A linear perturbation theory is derived in the absence of density gradients and hydrodynamical effects, and yields unstable solutions which propagate as magnetothermal waves. The theory is compared with full non-linear simulation in the context of a recent nanosecond gas-jet experiment and found to be in good agreement; exhibiting typical growth-rates and characteristic wavelengths of order 10ns-1 and 50µ m respectively. Further incorporation of density gradients and hydrodynamics into the magnetothermal stability analysis is shown to introduce the well-known field generating thermal instability source term, which can either complement or counteract the magnetothermal mechanism. Inequalities for predicting the dominance of each process are given: of the two, the magnetothermal mechanism is found to represent the main-and sometimes only-source of unstable feedback for the conditions considered here. Using super-Gaussian transport theory, the implications of inverse-bremmstrahlung heating for transport in laser-plasmas are also explored. Super-Gaussian modifications are shown to suppress a number of classical processes, by up to ~90% in some cases, while simultaneously introducing new effects, such as advection of magnetic field up density gradients. The combined consequences of these modifications are considered for the field generating thermal instability, and super-Gaussian effects are found to reduce growthrates by [greater than or similar to] 80% compared to predictions from classical transport theory under inertial confinement fusion conditions. The development of a unique code CTC, written to assist the exploration of both classical and super-Gaussian transport phenomena, and the new magnetothermal instability, is also described.
Subjects/Keywords: 535
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APA ·
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APA (6th Edition):
Bissell, J. J. (2012). Magnetised transport and instability in laser produced plasmas. (Doctoral Dissertation). Imperial College London. Retrieved from http://hdl.handle.net/10044/1/9176
Chicago Manual of Style (16th Edition):
Bissell, John Joseph. “Magnetised transport and instability in laser produced plasmas.” 2012. Doctoral Dissertation, Imperial College London. Accessed September 21, 2019.
http://hdl.handle.net/10044/1/9176.
MLA Handbook (7th Edition):
Bissell, John Joseph. “Magnetised transport and instability in laser produced plasmas.” 2012. Web. 21 Sep 2019.
Vancouver:
Bissell JJ. Magnetised transport and instability in laser produced plasmas. [Internet] [Doctoral dissertation]. Imperial College London; 2012. [cited 2019 Sep 21].
Available from: http://hdl.handle.net/10044/1/9176.
Council of Science Editors:
Bissell JJ. Magnetised transport and instability in laser produced plasmas. [Doctoral Dissertation]. Imperial College London; 2012. Available from: http://hdl.handle.net/10044/1/9176
22.
Skopalova, Eva.
The interaction of intense few-cycle laser pulses with nanoscale targets.
Degree: PhD, 2011, Imperial College London
URL: http://hdl.handle.net/10044/1/6884
► In this thesis I describe investigations of the interaction of strong laser fields with nanoscale targets, particularly with atomic clusters. I have explored laser-irradiated clusters…
(more)
▼ In this thesis I describe investigations of the interaction of strong laser fields with nanoscale targets, particularly with atomic clusters. I have explored laser-irradiated clusters in a new regime of interaction where the pulse duration approaches the few-cycle regime and the cluster ions essentially do not move during the laser pulse. A key result of this thesis is the observation of a new anisotropy in the ion emission from the explosion of xenon and argon clusters subjected to ultra-short (∼ 30 fs) near-infrared high intensity (∼ 1015 Wcm−2) laser pulses. In this regime more energetic ions are emitted in the direction perpendicular to the laser polarisation axis, which is the reverse of the well-known anisotropy previously observed in experiments with longer (∼ 100 fs) pulses. I show that the new anisotropy is a transient phenomenon present for a limited range of pulse durations, that is specific to the cluster size and atom species. As the pulse duration is increased the new anisotropy diminishes and a standard anisotropy appears. To explain the observed anisotropy, I have developed an electrostatic model, showing that the intracluster electric field can have a maximum in the direction perpendicular to the laser polarisation axis, leading to anisotropic ion acceleration consistent with experimental observations. These measurements and modeling give access to the initial dynamics, present early in the interaction of an intense laser field with a nanoscale dielectric. In addition to investigations of gas phase clusters I have also studied nanostructures on surfaces. An experiment to study time-dependent plasmonic fields with attosecond streaking is being designed and built. Here I present numerical simulations of nanoplasmonic streaking and address the issues that have to be considered for the ongoing experiment. I show how the plasmonic field can be retrieved from the simulated streaked spectra.
Subjects/Keywords: 535
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APA ·
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MLA ·
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CSE |
Export
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APA (6th Edition):
Skopalova, E. (2011). The interaction of intense few-cycle laser pulses with nanoscale targets. (Doctoral Dissertation). Imperial College London. Retrieved from http://hdl.handle.net/10044/1/6884
Chicago Manual of Style (16th Edition):
Skopalova, Eva. “The interaction of intense few-cycle laser pulses with nanoscale targets.” 2011. Doctoral Dissertation, Imperial College London. Accessed September 21, 2019.
http://hdl.handle.net/10044/1/6884.
MLA Handbook (7th Edition):
Skopalova, Eva. “The interaction of intense few-cycle laser pulses with nanoscale targets.” 2011. Web. 21 Sep 2019.
Vancouver:
Skopalova E. The interaction of intense few-cycle laser pulses with nanoscale targets. [Internet] [Doctoral dissertation]. Imperial College London; 2011. [cited 2019 Sep 21].
Available from: http://hdl.handle.net/10044/1/6884.
Council of Science Editors:
Skopalova E. The interaction of intense few-cycle laser pulses with nanoscale targets. [Doctoral Dissertation]. Imperial College London; 2011. Available from: http://hdl.handle.net/10044/1/6884
23.
Darios, Delphine.
Investigation of photoelectrons from molecules in a strong field.
Degree: PhD, 2010, Imperial College London
URL: http://hdl.handle.net/10044/1/5541
► When intense and few-cycle laser pulses interact with an atomic/molecular beam highorder Above Threshold Ionisation (HATI) can take place. The resulting electrons can be re-scattered…
(more)
▼ When intense and few-cycle laser pulses interact with an atomic/molecular beam highorder Above Threshold Ionisation (HATI) can take place. The resulting electrons can be re-scattered from the parent atoms/molecules and gain kinetic energy. The HATI electrons contain information about the atomic/molecular structure thus providing a method to probe atomic and molecular dynamics with sub-fs temporal and sub-angström spatial resolution. In this thesis the development of a Velocity Map Imaging apparatus capable of measuring the two-dimensional (2D) projection of the velocity distribution of electrons with energies up to 400 eV is described. This device was implemented with a molecular beam apparatus to study the electron re-scattering process that occurs when atoms/molecules are subjected to strong laser fields. Time-of-fight measurements were carried out to find the molecular beam. To perform the experiments a method to generate intense and few-cycle pulses based on hollow fibre pulse compression has been implemented. Pulses of 14 fs with energies of 500 μJ have been measured in a differentially pumped fibre set-up, with input pulses of 42 fs and 700 μJ using a home-made Frequency-Resolved Optical Gating device. The performance of the VMI apparatus was investigated by first studying the ATI rings formed by low energy electrons. Then, a study of the high energy electrons was carried out in different gases and re-scattered electrons with energies up to 100 eV were measured. The photoelectron spectra recorded with linearly polarised laser exhibit a plateau with a cut-off at 10 UP that is a characteristic of the re-scattering process. The observation of rescattered electrons was confirmed by two techniques: comparison of the data obtained with vertical polarisation (re-scattering) and circular polarisation (no re-scattering) and analysis of the structure in the angular distribution obtained in Xenon.
Subjects/Keywords: 535
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APA ·
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MLA ·
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CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Darios, D. (2010). Investigation of photoelectrons from molecules in a strong field. (Doctoral Dissertation). Imperial College London. Retrieved from http://hdl.handle.net/10044/1/5541
Chicago Manual of Style (16th Edition):
Darios, Delphine. “Investigation of photoelectrons from molecules in a strong field.” 2010. Doctoral Dissertation, Imperial College London. Accessed September 21, 2019.
http://hdl.handle.net/10044/1/5541.
MLA Handbook (7th Edition):
Darios, Delphine. “Investigation of photoelectrons from molecules in a strong field.” 2010. Web. 21 Sep 2019.
Vancouver:
Darios D. Investigation of photoelectrons from molecules in a strong field. [Internet] [Doctoral dissertation]. Imperial College London; 2010. [cited 2019 Sep 21].
Available from: http://hdl.handle.net/10044/1/5541.
Council of Science Editors:
Darios D. Investigation of photoelectrons from molecules in a strong field. [Doctoral Dissertation]. Imperial College London; 2010. Available from: http://hdl.handle.net/10044/1/5541
24.
Hoffmann, David.
High harmonic generation using multicolour fields.
Degree: PhD, 2011, Imperial College London
URL: http://hdl.handle.net/10044/1/9149
► This thesis describes the phenomenon of high harmonic generation from atoms irradiated by intense, ultrashort laser pulses. Particular attention is paid to the benefits achieved…
(more)
▼ This thesis describes the phenomenon of high harmonic generation from atoms irradiated by intense, ultrashort laser pulses. Particular attention is paid to the benefits achieved by using multicolour driving fields. A theoretical description of few-cycle laser pulses is presented, together with their interaction with free-electrons and the role they play in various nonlinear optical processes. A number of numerical models are presented to simulate high harmonic generation from atomic systems. These are used to analyse and explain the temporal structure of the emitted high-frequency dipole radiation. Propagation of the macroscopic harmonic response through a gaseous volume is modelled and the role of phase-matching explained in detail. We consider focussing geometry in optimising the yield of particular harmonics, together with the effects of free-electrons within the interaction region. We discuss means by which multicolour fields may overcome some of the constraints of single-colour high harmonic generation. Using two delayed pulses of the same frequency and parallel polarisation we demonstrate significant cut-off extension without increasing total ionisation throughout the pulse, crucial for maintaining harmonic yield close to the saturation limit. We also explain the significant yield enhancements observed in recent experiments using two parallel colours of incommensurate frequency. Finally, we describe the use of a second, perpendicularly polarised colour in trajectory selection, allowing for a temporal filtering of harmonic emission. Using an ω + 1.5ω frequency ratio also allows for a reduction in the periodicity of emitted attosecond pulse trains, permitting the production of isolated attosecond pulses with longer driving fields. Furthermore, by controlling the relative phase between the two colours, the ellipticity of these attosecond pulses may also be controlled.
Subjects/Keywords: 535
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APA ·
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Export
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Manager
APA (6th Edition):
Hoffmann, D. (2011). High harmonic generation using multicolour fields. (Doctoral Dissertation). Imperial College London. Retrieved from http://hdl.handle.net/10044/1/9149
Chicago Manual of Style (16th Edition):
Hoffmann, David. “High harmonic generation using multicolour fields.” 2011. Doctoral Dissertation, Imperial College London. Accessed September 21, 2019.
http://hdl.handle.net/10044/1/9149.
MLA Handbook (7th Edition):
Hoffmann, David. “High harmonic generation using multicolour fields.” 2011. Web. 21 Sep 2019.
Vancouver:
Hoffmann D. High harmonic generation using multicolour fields. [Internet] [Doctoral dissertation]. Imperial College London; 2011. [cited 2019 Sep 21].
Available from: http://hdl.handle.net/10044/1/9149.
Council of Science Editors:
Hoffmann D. High harmonic generation using multicolour fields. [Doctoral Dissertation]. Imperial College London; 2011. Available from: http://hdl.handle.net/10044/1/9149
25.
Seem, Peter R.
Optical scattering for security applications.
Degree: PhD, 2009, Imperial College London
URL: http://hdl.handle.net/10044/1/5502
► Laser Surface Authentication (LSA) has emerged in recent years as a potentially disruptive tracking and authentication technology. A strong need for such a solution in…
(more)
▼ Laser Surface Authentication (LSA) has emerged in recent years as a potentially disruptive tracking and authentication technology. A strong need for such a solution in a variety of industries drove the implementation of the technology faster than the scientific understanding could keep up. The drive to miniaturise and simplify, the need to be robust against real-world problems like damage and misuse, and not least, intellectual curiosity, make it clear that a firmer scientific footing is important as the technology matures. Existing scattering and biometric work are reviewed, and LSA is introduced as a technology. The results of field-work highlight the restrictions which are encountered when the technology is applied. Analysis of the datasets collected in the trial provide, first, an indication of the performance of LSA under real-world conditions and, second, insight into the potential shortcomings of the technique. Using the particulars of the current sensor’s geometry, the LSA signal is characterised. Measurements are made of the decorrelation of the signature with linear and rotational offsets, and it is concluded that while surface microstructure has a strong impact on the rate of decorrelation, this dependency is not driven by the surface’s feature size. A new series of experiments examine that same decorrelation for interference effects with different illumination conditions, and conclude that laser speckle is not an adequate explanation for the phenomenon. The results of this experimental work inform a mathematical description of LSA based on a combination of existing bi-static scattering models used in physics and ray-tracing, which is implemented numerically. The results of the model are found to be a good fit to experimental work, and new predictions are made about LSA.
Subjects/Keywords: 535
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APA (6th Edition):
Seem, P. R. (2009). Optical scattering for security applications. (Doctoral Dissertation). Imperial College London. Retrieved from http://hdl.handle.net/10044/1/5502
Chicago Manual of Style (16th Edition):
Seem, Peter R. “Optical scattering for security applications.” 2009. Doctoral Dissertation, Imperial College London. Accessed September 21, 2019.
http://hdl.handle.net/10044/1/5502.
MLA Handbook (7th Edition):
Seem, Peter R. “Optical scattering for security applications.” 2009. Web. 21 Sep 2019.
Vancouver:
Seem PR. Optical scattering for security applications. [Internet] [Doctoral dissertation]. Imperial College London; 2009. [cited 2019 Sep 21].
Available from: http://hdl.handle.net/10044/1/5502.
Council of Science Editors:
Seem PR. Optical scattering for security applications. [Doctoral Dissertation]. Imperial College London; 2009. Available from: http://hdl.handle.net/10044/1/5502
26.
Cumberland, Burly.
Wavelength extension in speciality fibres.
Degree: PhD, 2009, Imperial College London
URL: http://hdl.handle.net/10044/1/5510
► Since the invention of the laser and its first application, there has been an almost continuous stream of new applications - many of which require…
(more)
▼ Since the invention of the laser and its first application, there has been an almost continuous stream of new applications - many of which require specific laser sources. These applications often require a laser source with a specific power, pulse duration, energy and wavelength. In some cases these demands are easily met, whilst in others they have proven rather more difficult to achieve. Traditionally, wavelength versatility has been limited to the regions for which rare earth or gas gain media are available. These lasers themselves can be used to generate other wavelengths through the nonlinear processes of second and third harmonic generation, as well as sum frequency generation. Despite all of this, there still exists a significant section of the visible and infrared spectrum for which no convenient sources exist. This thesis is concerned with the development of sources in these regions along with broadband sources covering significant portions of the spectrum by themselves. These new wavelengths are generated in a variety of speciality fibres using either nonlinear processes or new gain media doped into standard silica fibres. Three types of speciality fibre are used: low concentration bismuth doped fibre which provides gain in the 1.0-1.4 μm region; photonic crystal fibres; and very high (75%) concentration germanium fibres to generate a laser source at 2.1 μm based upon stimulated Raman scattering. Photonic crystal fibres provide high nonlinearities and controllable dispersion which enables the generation of broadband supercontinuum sources based upon the interaction of many nonlinear effects. Each source will be described in depth, with particular attention given to the underlying physics that gives rise to the source. Previous and current limitations will be examined and an outlook of the future development of such sources will be discussed.
Subjects/Keywords: 535
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APA (6th Edition):
Cumberland, B. (2009). Wavelength extension in speciality fibres. (Doctoral Dissertation). Imperial College London. Retrieved from http://hdl.handle.net/10044/1/5510
Chicago Manual of Style (16th Edition):
Cumberland, Burly. “Wavelength extension in speciality fibres.” 2009. Doctoral Dissertation, Imperial College London. Accessed September 21, 2019.
http://hdl.handle.net/10044/1/5510.
MLA Handbook (7th Edition):
Cumberland, Burly. “Wavelength extension in speciality fibres.” 2009. Web. 21 Sep 2019.
Vancouver:
Cumberland B. Wavelength extension in speciality fibres. [Internet] [Doctoral dissertation]. Imperial College London; 2009. [cited 2019 Sep 21].
Available from: http://hdl.handle.net/10044/1/5510.
Council of Science Editors:
Cumberland B. Wavelength extension in speciality fibres. [Doctoral Dissertation]. Imperial College London; 2009. Available from: http://hdl.handle.net/10044/1/5510
27.
Frank, Felix.
Generation and application of ultrashort laser pulses in attosecond science.
Degree: PhD, 2011, Imperial College London
URL: http://hdl.handle.net/10044/1/7025
► In this thesis, I describe the development of a sub-4 fs few-cycle laser system at Imperial College London used to generate and characterise the first…
(more)
▼ In this thesis, I describe the development of a sub-4 fs few-cycle laser system at Imperial College London used to generate and characterise the first single attosecond (1 as = 10-18s) pulses in the UK. Phase-stabilised few-cycle laser pulses were generated using a hollow fibre system with a chirped mirror compression setup. The pulse was fully characterised using frequency-resolved optical gating (FROG) and spectral phase interferometry for direct electric field reconstruction in a spatially encoded filter arrangement (SEA-F-SPIDER). A pulse duration of 3.5 fs was measured with an argon filled hollow fibre. These phase stabilised Infra-Red (IR) pulses were used to generate a continuous spectrum of high harmonics in the Extreme Ultraviolet (XUV) originating from a single half-cycle of the driving field. Using subsequent spectral filtering, a single attosecond pulse was generated. The isolated XUV pulse was characterised using an atomic streaking camera and a pulse duration of ~260 as was retrieved using FROG for complete reconstruction of attosecond bursts (FROG-CRAB). In an experiment conducted at the Rutherford Appleton Laboratory, high harmonics were generated using a two-colour field with an energetic beam at 1300nm and a weak second harmonic orthogonally polarized to the fundamental. By changing the phase between the two fields, a deep modulation of the harmonic yield is seen and an enhancement of one order of magnitude compared to the single colour field with the same energy is observed.
Subjects/Keywords: 535
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APA (6th Edition):
Frank, F. (2011). Generation and application of ultrashort laser pulses in attosecond science. (Doctoral Dissertation). Imperial College London. Retrieved from http://hdl.handle.net/10044/1/7025
Chicago Manual of Style (16th Edition):
Frank, Felix. “Generation and application of ultrashort laser pulses in attosecond science.” 2011. Doctoral Dissertation, Imperial College London. Accessed September 21, 2019.
http://hdl.handle.net/10044/1/7025.
MLA Handbook (7th Edition):
Frank, Felix. “Generation and application of ultrashort laser pulses in attosecond science.” 2011. Web. 21 Sep 2019.
Vancouver:
Frank F. Generation and application of ultrashort laser pulses in attosecond science. [Internet] [Doctoral dissertation]. Imperial College London; 2011. [cited 2019 Sep 21].
Available from: http://hdl.handle.net/10044/1/7025.
Council of Science Editors:
Frank F. Generation and application of ultrashort laser pulses in attosecond science. [Doctoral Dissertation]. Imperial College London; 2011. Available from: http://hdl.handle.net/10044/1/7025
28.
Brugnera, Leonardo.
Control of high harmonic generation by manipulation of field parameters.
Degree: PhD, 2011, Imperial College London
URL: http://hdl.handle.net/10044/1/9151
► ?High harmonic generation is a well established technique to investigate the structure and the inner dynamics of atoms and molecules. This thesis describes how the…
(more)
▼ ?High harmonic generation is a well established technique to investigate the structure and the inner dynamics of atoms and molecules. This thesis describes how the generating field parameters can be manipulated to extend the limits imposed on the technique by the use of traditional laser sources. In this field, with traditional source we mean high intensity, linearly polarised laser pulses at 800 nm. The first parameter to be investigated is the wavelength λ of the generating beam. The unfavourable scaling of the high harmonic yield with λ seems to suggest that high harmonic spectroscopy of atoms and molecules should be restricted to the wavelengths that obviate this problem, and that therefore shorter wavelength should be used. But longer wavelengths, in the mid infrared, present a great advantage respect to shorter ones. The maximum harmonic order that we can obtain is proportional to the ionisation potential of the target and to the wavelength times the intensity of the beam, so a higher number of harmonic can be produced with a longer wavelength than with short, the intensity being equal. This becomes incredibly valuable when the specie under investigation is a molecule with low ionisation potential. To produce high harmonics, a linearly polarised beam is required. If ellipticity is introduced in the beam, the harmonic signal quickly fades out, as non-linearly polarisation in monochromatic beams switches off the mechanism at the basis of high harmonic generation. This is not true if the polarisation of the beam is changed through the introduction of an additional laser beam, perpendicularly polarised respect to the fundamental. In this thesis the additional degree of freedom that this second field implies is investigated by combining the fundamental with its second harmonic and by controlling the relative delay of the two with sub-cycle precision. The key result is that the addition of the second harmonic gives access to the control of the harmonic amplitude and to the time at which the high harmonics are emitted, by simply controlling the relative phase between the two pulses.
Subjects/Keywords: 535
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APA ·
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CSE |
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APA (6th Edition):
Brugnera, L. (2011). Control of high harmonic generation by manipulation of field parameters. (Doctoral Dissertation). Imperial College London. Retrieved from http://hdl.handle.net/10044/1/9151
Chicago Manual of Style (16th Edition):
Brugnera, Leonardo. “Control of high harmonic generation by manipulation of field parameters.” 2011. Doctoral Dissertation, Imperial College London. Accessed September 21, 2019.
http://hdl.handle.net/10044/1/9151.
MLA Handbook (7th Edition):
Brugnera, Leonardo. “Control of high harmonic generation by manipulation of field parameters.” 2011. Web. 21 Sep 2019.
Vancouver:
Brugnera L. Control of high harmonic generation by manipulation of field parameters. [Internet] [Doctoral dissertation]. Imperial College London; 2011. [cited 2019 Sep 21].
Available from: http://hdl.handle.net/10044/1/9151.
Council of Science Editors:
Brugnera L. Control of high harmonic generation by manipulation of field parameters. [Doctoral Dissertation]. Imperial College London; 2011. Available from: http://hdl.handle.net/10044/1/9151
29.
Shardlow, Peter Charles.
Enhancement of self-organisation and adaptivity in laser systems.
Degree: PhD, 2010, Imperial College London
URL: http://hdl.handle.net/10044/1/6133
► Self-organisation is an inherent mechanism in all laser systems although it is often overlooked. The self formation of spatial and spectral modes, competition between modes…
(more)
▼ Self-organisation is an inherent mechanism in all laser systems although it is often overlooked. The self formation of spatial and spectral modes, competition between modes and much spatio-temporal dynamics are driven by the intrinsic non-linearity of saturable gain in the laser amplifier medium coupled with feedback from a resonator structure. It is highly insightful to consider the growth, extinction and competition of modes in a laser system as an evolving ecosystem with modes as species growing by stimulated emission in the gain medium, decaying by intracavity and output coupling losses, and having to compete for the common, but finite, resource of gain which is supplied by an external excitation source. The outcome of species competition is a survival-of-the-fittest that determines the final steady-state output or dynamical set of modes that can continue to persist. This thesis presents investigations into the design solid-state laser systems which utilise the inherent dynamics of optical fields and gain media in order to self-organise the system to operate in a desirable manner. The Nd:YVO4 bounce geometry laser amplifier is employed throughout this thesis. A numerical investigation of the thermally induced lensing within the laser crystal is reported. Optimisation of the geometry parameters is explored as well as investigation into future developments, such as the utilisation of an additional sapphire crystal to directly cool the laser crystal pump face. This is shown to theoretically reduce the horizontal thermally induced lens strengths by a factor of 4. Single longitudinal mode single longitudinal mode (SLM) ring lasers where the unidirectionality is imposed either by an extra-cavity ‘parasitic’ pass of the gain media or by retro-reflection of one of the two outputs are investigated. SLM TEM00 output powers of up to 20W are demonstrated without the need for a Faraday isolator. A self-adaptive sensor which allows the measurement of remote surface vibrations is demonstrated. The two-wave mixing interaction within a saturable gain media is shown to allow measurement of high frequency phase modulations (>10kHz) whilst adapting to cancel out low frequency perturbations. This sensor system is shown to have potential as a remote ultrasound detector as the holographic nature allows high frequency measurement of the vibrations of rough remote surfaces. Self-starting self-adaptive lasers, where a four wave mixing interaction within the saturable gain medium is utilised to generate phase conjugate and aberration corrective laser systems are experimentally investigated. This work is extended to show that the gain hologram is capable of adapting to low frequency phase modulations in order to maintain a high quality output. A demonstration of self-organised coherent beam combination of two bounce geometry laser oscillators into a single output beam is reported. A combined output beam of 35.7W was demonstrated from 94W of pump power. This coherent beam combination is extended into the technique of phase conjugate…
Subjects/Keywords: 535
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Record Details
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APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
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APA (6th Edition):
Shardlow, P. C. (2010). Enhancement of self-organisation and adaptivity in laser systems. (Doctoral Dissertation). Imperial College London. Retrieved from http://hdl.handle.net/10044/1/6133
Chicago Manual of Style (16th Edition):
Shardlow, Peter Charles. “Enhancement of self-organisation and adaptivity in laser systems.” 2010. Doctoral Dissertation, Imperial College London. Accessed September 21, 2019.
http://hdl.handle.net/10044/1/6133.
MLA Handbook (7th Edition):
Shardlow, Peter Charles. “Enhancement of self-organisation and adaptivity in laser systems.” 2010. Web. 21 Sep 2019.
Vancouver:
Shardlow PC. Enhancement of self-organisation and adaptivity in laser systems. [Internet] [Doctoral dissertation]. Imperial College London; 2010. [cited 2019 Sep 21].
Available from: http://hdl.handle.net/10044/1/6133.
Council of Science Editors:
Shardlow PC. Enhancement of self-organisation and adaptivity in laser systems. [Doctoral Dissertation]. Imperial College London; 2010. Available from: http://hdl.handle.net/10044/1/6133
30.
Bellei, Claudio.
Measurements of optical radiation from high-intensity laser-plasma interactions.
Degree: PhD, 2009, Imperial College London
URL: http://hdl.handle.net/10044/1/5372
► This thesis presents experimental and theoretical results on the interaction of high-intensity lasers with solid and gaseous targets. All the measurements that are described belong…
(more)
▼ This thesis presents experimental and theoretical results on the interaction of high-intensity lasers with solid and gaseous targets. All the measurements that are described belong to the optical region of the spectrum. The interaction with solid targets has been investigated for two different intensity regimes. Intensities of up to 10[21] Wcm-2 have been accessed on the VULCAN laser system at the Rutherford Appleton Laboratory whereas the JETI laser system at the Institut für Optik und Quantenelektronik in Jena allowed to reach intensities of up to 4x10[19] Wcm-2 . For both regimes, the transport of relativistic electrons generated in the interactions has been investigated through measurements of the optical radiation emitted from the rear surface of the solid targets. Polarimetry and angular distribution measurements indicate that the radiation presents a high degree of polarisation and is non-isotropically emitted. It is, therefore, mainly attributed to transition radiation. A theoretical model has been developed in order to interpret and validate the experimental observations. As a result, for the high intensity regime variation of the signal strength of the transition radiation with respect to the direction of observation is attributed to the presence of mm-scale filaments. The interaction with gaseous targets has been investigated at the Astra Gemini facility at the Rutherford Appleton Laboratory, for peak intensities of up to 3x10[19] Wcm-2 in a spot size of 20 [Mu]m FWHM. In this experiment the properties of the laser pulse were studied after interaction with the targets. For this purpose, a second harmonic generation FROG device was used. This allowed to determine both the pulse duration and the temporal phase of the pulse, giving an insight on the dependence of the pulse properties with respect to interaction length and electron number density. The experimental results show that the nonlinear evolution of the pulse can lead to compression from 45 fs before the interaction to a single pulse of below 20 fs duration, after propagating in the gaseous medium.
Subjects/Keywords: 535
Record Details
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Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Bellei, C. (2009). Measurements of optical radiation from high-intensity laser-plasma interactions. (Doctoral Dissertation). Imperial College London. Retrieved from http://hdl.handle.net/10044/1/5372
Chicago Manual of Style (16th Edition):
Bellei, Claudio. “Measurements of optical radiation from high-intensity laser-plasma interactions.” 2009. Doctoral Dissertation, Imperial College London. Accessed September 21, 2019.
http://hdl.handle.net/10044/1/5372.
MLA Handbook (7th Edition):
Bellei, Claudio. “Measurements of optical radiation from high-intensity laser-plasma interactions.” 2009. Web. 21 Sep 2019.
Vancouver:
Bellei C. Measurements of optical radiation from high-intensity laser-plasma interactions. [Internet] [Doctoral dissertation]. Imperial College London; 2009. [cited 2019 Sep 21].
Available from: http://hdl.handle.net/10044/1/5372.
Council of Science Editors:
Bellei C. Measurements of optical radiation from high-intensity laser-plasma interactions. [Doctoral Dissertation]. Imperial College London; 2009. Available from: http://hdl.handle.net/10044/1/5372
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Open Access Theses and Dissertations