+publisher:"University of Colorado" +contributor:("Steven T. Cundiff")

University of Colorado

1. Chao, Qing. Optical Imaging in Scattering Medium Using Supercontinuum Laser and the Effects of Polarization.

Degree: PhD, 2017, University of Colorado

URL: https://scholar.colorado.edu/ecen_gradetds/145

► As optical imaging in scattering medium is emerging as a promising imaging modality, several challenges arise against deeper imaging due to the multiple-scattering caused… (more)

▼ As optical imaging in scattering medium is emerging as a promising imaging modality, several challenges arise against deeper imaging due to the multiple-scattering caused by the inhomogeneous distribution of refractive index. To obtain high quality images through active structured light illumination and polarization imaging, an polarized, tunable and intense broadband light source is highly desirable to perform coherence gating for enhancing ballistic photons in a highly scattering medium. This thesis describes the challenges of optical imaging, polarization imaging in scattering medium, the experimental investigations of a dynamic structured illumination microscope (DSIM), and the development of a versatile broadband supercontinuum light source generated using ultra fast nonlinear optics for enabling new optical imaging modalities in scattering medium. The DSIM was demonstrated as a Fourier synthesis and polarization-sensitive imaging method using a moving illumination pattern requiring only a single pixel camera or a photodiode detector. To increase penetration depth in a scattering medium, it is suggested that a broadband supercontinuum laser can be used as a powerful and tunable ﬁber-based light source for coherence gating to enhance ballistic photons. Therefore, an octave-spanning broadband supercontinuum light laser is experimentally demonstrated using an ultrafast femtosecond Ti:Sapphire seed laser and a highly nonlinear micro-structured photonics crystal ﬁber. During the experiment, the broadband supercontinuum output is demonstrated to be polarization-dependent, thus a detailed numerical simulation is developed using vectorized generalized nonlinear Schr¨odinger equations (GNLSE) for both isotropic and anisotropic ﬁber mediums. The polarization trajectories of Raman solitons in the supercontinuum generation visualized on the Poincar´e sphere reveals rich polarization dynamics, including a polarization separatrix for light propagation in the birefringent ﬁber. While most of the previous works were focused on polarization dynamics for light propagation in linearly birefringent ﬁber, I investigated the case of circularly birefringent ﬁber and found a simpliﬁed polarization evolution that leads to a motivation for developing twisted ﬁbers for single polarization broadband light sources. The versatile and stable circularly polarized broadband supercontinuum can be potentially one of the most attractive light source to improve optical imaging in scattering medium. Advisors/Committee Members: Kelvin H. Wagner, Daniel Feldkhun, Steven T. Cundiff.

Subjects/Keywords: nonlinear optics; optical imaging; polarization; scattering medium; supercontinuum; Optics

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APA (6^th Edition):

Chao, Q. (2017). Optical Imaging in Scattering Medium Using Supercontinuum Laser and the Effects of Polarization. (Doctoral Dissertation). University of Colorado. Retrieved from https://scholar.colorado.edu/ecen_gradetds/145

Chicago Manual of Style (16^th Edition):

Chao, Qing. “Optical Imaging in Scattering Medium Using Supercontinuum Laser and the Effects of Polarization.” 2017. Doctoral Dissertation, University of Colorado. Accessed April 13, 2021. https://scholar.colorado.edu/ecen_gradetds/145.

MLA Handbook (7^th Edition):

Chao, Qing. “Optical Imaging in Scattering Medium Using Supercontinuum Laser and the Effects of Polarization.” 2017. Web. 13 Apr 2021.

Vancouver:

Chao Q. Optical Imaging in Scattering Medium Using Supercontinuum Laser and the Effects of Polarization. [Internet] [Doctoral dissertation]. University of Colorado; 2017. [cited 2021 Apr 13]. Available from: https://scholar.colorado.edu/ecen_gradetds/145.

Council of Science Editors:

Chao Q. Optical Imaging in Scattering Medium Using Supercontinuum Laser and the Effects of Polarization. [Doctoral Dissertation]. University of Colorado; 2017. Available from: https://scholar.colorado.edu/ecen_gradetds/145

University of Colorado

2. He, Long. Optical Second Harmonic Generation Measurements for Characterization of Amorphous Silicon Interfaces.

Degree: PhD, Physics, 2014, University of Colorado

URL: https://scholar.colorado.edu/phys_gradetds/1

► Hydrogenated amorphous silicon films (a-Si:H) have a long history of application in optoelectronic devices, in part due to their low cost and compatibility with… (more)

▼ Hydrogenated amorphous silicon films (a-Si:H) have a long history of application in optoelectronic devices, in part due to their low cost and compatibility with large area substrates. Recently, crystal silicon/a-Si:H heterojunction(SHJ) photovoltaic cells have demonstrated extremely high open circuit voltages (V_OC = 750 mV) and photo-conversion efficiencies (24.7%). In SHJ PVs, the amorphous-crystalline silicon (a-Si:H/c-Si) interface is the critical aspect of the device to optimize for high efficiency. The understanding of defects and transport at the a-Si:H/c-Si junction has been slow to develop due to a dearth of optoelectronic measurements able to distinguish the unique interface physics from effects in the bulk a-Si:H and c-Si volumes. Optical second harmonic generation (SHG) has been extensively used to selectively characterize surfaces and interface in a variety of materials, including semiconductors. In SHG experiments, interfaces and surfaces can be probed selectively: One focuses a pulsed laser beam (frequency ω) onto the sample and detects second harmonic light (frequency 2ω) generated at optically accessible surfaces and interfaces in the sample. SHG elucidates the important interface properties because the bulk "background" is mostly forbidden by symmetry in cubic and amorphous materials, leaving only interface contributions. In this thesis, I have demonstrated that SHG is a sensitive tool for probing strong electric field present in the 10 nm a-Si:H layer in SHJ solar cells. To study the electric-field induced SHG (EFISH) in a-Si:H, we measure SHG from ITO/a-Si:H/ITO sandwich structures at different biases and polarization geometries. In this "simple" structure, we quantitatively separate interface SHG and EFISH. We also directly probe carrier dynamics in the depletion region of a ITO/a-Si:H junction with time-resolved optical second-harmonic generation. Through fitting of the time-resolved SHG data and current data simultaneously, we are able to show that slow carrier dynamics that are visible in the device current are actually taking place within the ITO/a-Si interfacial region. In summary, SHG is proven to be a promising diagnostic method to characterize the interface electrostatics and charge transport at the amorphous silicon interfaces. Advisors/Committee Members: Charles T. Rogers, Charles W. Teplin, Steven T. Cundiff.

Subjects/Keywords: amorphous silicon; charge transportation; heterojunction; interface; Second Harmonic Generation; solar cell; Condensed Matter Physics; Optics

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APA (6^th Edition):

He, L. (2014). Optical Second Harmonic Generation Measurements for Characterization of Amorphous Silicon Interfaces. (Doctoral Dissertation). University of Colorado. Retrieved from https://scholar.colorado.edu/phys_gradetds/1

Chicago Manual of Style (16^th Edition):

He, Long. “Optical Second Harmonic Generation Measurements for Characterization of Amorphous Silicon Interfaces.” 2014. Doctoral Dissertation, University of Colorado. Accessed April 13, 2021. https://scholar.colorado.edu/phys_gradetds/1.

MLA Handbook (7^th Edition):

He, Long. “Optical Second Harmonic Generation Measurements for Characterization of Amorphous Silicon Interfaces.” 2014. Web. 13 Apr 2021.

Vancouver:

He L. Optical Second Harmonic Generation Measurements for Characterization of Amorphous Silicon Interfaces. [Internet] [Doctoral dissertation]. University of Colorado; 2014. [cited 2021 Apr 13]. Available from: https://scholar.colorado.edu/phys_gradetds/1.

Council of Science Editors:

He L. Optical Second Harmonic Generation Measurements for Characterization of Amorphous Silicon Interfaces. [Doctoral Dissertation]. University of Colorado; 2014. Available from: https://scholar.colorado.edu/phys_gradetds/1

University of Colorado

3. Zhang, Haipeng. Linear and Nonlinear Electro-optics In a Semiconductor.

Degree: PhD, Electrical, Computer & Energy Engineering, 2012, University of Colorado

URL: https://scholar.colorado.edu/ecen_gradetds/54

► Numerous investigative efforts have been made to study the properties of semiconductor materials, which are the foundation of modern electronics. In this dissertation, we… (more)

Subjects/Keywords: Electrical and Computer Engineering; Optics; Physics

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APA (6^th Edition):

Zhang, H. (2012). Linear and Nonlinear Electro-optics In a Semiconductor. (Doctoral Dissertation). University of Colorado. Retrieved from https://scholar.colorado.edu/ecen_gradetds/54

Chicago Manual of Style (16^th Edition):

Zhang, Haipeng. “Linear and Nonlinear Electro-optics In a Semiconductor.” 2012. Doctoral Dissertation, University of Colorado. Accessed April 13, 2021. https://scholar.colorado.edu/ecen_gradetds/54.

MLA Handbook (7^th Edition):

Zhang, Haipeng. “Linear and Nonlinear Electro-optics In a Semiconductor.” 2012. Web. 13 Apr 2021.

Vancouver:

Zhang H. Linear and Nonlinear Electro-optics In a Semiconductor. [Internet] [Doctoral dissertation]. University of Colorado; 2012. [cited 2021 Apr 13]. Available from: https://scholar.colorado.edu/ecen_gradetds/54.

Council of Science Editors:

Zhang H. Linear and Nonlinear Electro-optics In a Semiconductor. [Doctoral Dissertation]. University of Colorado; 2012. Available from: https://scholar.colorado.edu/ecen_gradetds/54

University of Colorado

4. Autry, Travis Marshall. Cavity QED with Exciton Polaritons Using Two-Dimensional Coherent Spectroscopy.

Degree: PhD, 2017, University of Colorado

URL: https://scholar.colorado.edu/phys_gradetds/277

► In semiconductors the band edge absorption properties are dominated by Coulomb bound electron-hole pairs known as excitons. In an isotropic ideal infinite crystal such… (more)

▼ In semiconductors the band edge absorption properties are dominated by Coulomb bound electron-hole pairs known as excitons. In an isotropic ideal infinite crystal such as a bulk semiconductors the exciton does not decay to a ground state but instead exchanges energy with the internal modes of the electromagnetic field found from the same boundary conditions as the crystal. It is only the leakage of photons out of the crystal due to real crystals having finite size that allows the exciton-light field to decay. This exchange of energy led to the concept of the exciton-polariton which represents the coupled system of exciton and light. In this work we bring novel insight into the behavior of excitons and exciton-polaritons using a new tool for performing of multidimensional coherent spectroscopy (MDCS) experiments. We first present a new realization of MDCS using a collinear approach to record a nonlinear wave-mixing signal as a photocurrent. This approach has many advantages over conventional approaches to MDCS as it allows for microscopy and the study of single nano-objects while recording the phase and amplitude of these signals. To achieve the strong coupling regime in semiconductors a semiconductor microcavity is often grown around a quantum well. When optically excited the quantum well exciton exchanges energy with the electromagnetic field resulting in new normal modes. These normal modes are called exciton-polaritons. The strong coupling regime is typically characterized by an avoided crossing measured as a function of exciton-cavity detuning. In polariton systems, the new normal modes result in quasiparticles with very small mass due to the photonic component of the system. As a result the detuning becomes a dispersion relation. We explore the higher lying dispersion curves of exciton-polaritons in a semiconductor microcavity by utilizing a pulse sequence that creates higher order coherences, i.e. coherences between states with an energy difference of Δn > 1. By recording this coherence as a function of detuning we are able to map out the strong coupling for these higher lying states bringing new insight into the nature of strong coupling and the bosonic nature of polaritons. Advisors/Committee Members: Steven T. Cundiff, James K. Thompson, Muray Holland, Markus B. Raschke, Niels Damrauer.

Subjects/Keywords: exciton-polaritons; multidimensional spectroscopy; strong coupling; ultrafast spectroscopy; electromagnetic field; Optics; Physics

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APA (6^th Edition):

Autry, T. M. (2017). Cavity QED with Exciton Polaritons Using Two-Dimensional Coherent Spectroscopy. (Doctoral Dissertation). University of Colorado. Retrieved from https://scholar.colorado.edu/phys_gradetds/277

Chicago Manual of Style (16^th Edition):

Autry, Travis Marshall. “Cavity QED with Exciton Polaritons Using Two-Dimensional Coherent Spectroscopy.” 2017. Doctoral Dissertation, University of Colorado. Accessed April 13, 2021. https://scholar.colorado.edu/phys_gradetds/277.

MLA Handbook (7^th Edition):

Autry, Travis Marshall. “Cavity QED with Exciton Polaritons Using Two-Dimensional Coherent Spectroscopy.” 2017. Web. 13 Apr 2021.

Vancouver:

Autry TM. Cavity QED with Exciton Polaritons Using Two-Dimensional Coherent Spectroscopy. [Internet] [Doctoral dissertation]. University of Colorado; 2017. [cited 2021 Apr 13]. Available from: https://scholar.colorado.edu/phys_gradetds/277.

Council of Science Editors:

Autry TM. Cavity QED with Exciton Polaritons Using Two-Dimensional Coherent Spectroscopy. [Doctoral Dissertation]. University of Colorado; 2017. Available from: https://scholar.colorado.edu/phys_gradetds/277

University of Colorado

5. Semonin, Octavi Escala. Multiple Exciton Generation in Quantum Dot Solar Cells.

Degree: PhD, Physics, 2012, University of Colorado

URL: https://scholar.colorado.edu/phys_gradetds/66

► Photovoltaics are limited in their power conversion efficiency (PCE) by very rapid relaxation of energetic carriers to the band edge. Therefore, photons from the… (more)

Subjects/Keywords: carrier multiplication; excitonic emigration; nanocrystals; optical modeling; photovoltaics; surface chemistry; Chemistry; Materials Science and Engineering; Physics

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APA (6^th Edition):

Semonin, O. E. (2012). Multiple Exciton Generation in Quantum Dot Solar Cells. (Doctoral Dissertation). University of Colorado. Retrieved from https://scholar.colorado.edu/phys_gradetds/66

Chicago Manual of Style (16^th Edition):

Semonin, Octavi Escala. “Multiple Exciton Generation in Quantum Dot Solar Cells.” 2012. Doctoral Dissertation, University of Colorado. Accessed April 13, 2021. https://scholar.colorado.edu/phys_gradetds/66.

MLA Handbook (7^th Edition):

Semonin, Octavi Escala. “Multiple Exciton Generation in Quantum Dot Solar Cells.” 2012. Web. 13 Apr 2021.

Vancouver:

Semonin OE. Multiple Exciton Generation in Quantum Dot Solar Cells. [Internet] [Doctoral dissertation]. University of Colorado; 2012. [cited 2021 Apr 13]. Available from: https://scholar.colorado.edu/phys_gradetds/66.

Council of Science Editors:

Semonin OE. Multiple Exciton Generation in Quantum Dot Solar Cells. [Doctoral Dissertation]. University of Colorado; 2012. Available from: https://scholar.colorado.edu/phys_gradetds/66

University of Colorado

6. Courtney, Trevor Laurence. Bringing Two-Dimensional Fourier Transform Electronic Spectroscopy into the Short-Wave Infrared.

Degree: PhD, Chemistry & Biochemistry, 2012, University of Colorado

URL: https://scholar.colorado.edu/chem_gradetds/69

► Two-dimensional Fourier Transform (2D FT) spectroscopy in the short-wave infrared (1-2 &mu) enables high frequency and time resolution experiments of molecular dyes, third-generation photovoltaic… (more)

▼ Two-dimensional Fourier Transform (2D FT) spectroscopy in the short-wave infrared (1-2 &mu) enables high frequency and time resolution experiments of molecular dyes, third-generation photovoltaic systems, and carotenoids - all rich in electronic transitions in this spectral region. Such experiments require short pulses with broad spectra to probe fast dephasing or solvation dynamics as well as couplings between widely spaced electronic transitions. Stable, low-dispersion interferometers at Brewster's angle are introduced for multioctave-spanning nonlinear spectroscopies. We adapt a compact, phase-characterized Mach-Zehnder interferometer to the short-wave infrared; active stabilization produces accurate and evenly spaced time delays between the two excitation pulses in 2D FT spectroscopy. An intrinsically phase-stable Sagnac interferometer is introduced to enhance the interferometric signal detection with respect to the copropagating local oscillator in partially collinear 2D FT spectroscopy. These interferometers exploit the air-glass interface Brewster's angle of thin-film metallic beam splitters to preserve expected output phase shifts and to minimize secondary reflections over multiple octaves. A homebuilt short-wave IR noncollinear optical parametric amplifier with a periodically poled crystal provides broadband excitation and detection. The output pulses are compressed with a deformable mirror using second-harmonic generation feedback in a genetic algorithm to pulse durations as low as 10 fs. Together this light source and the interferometric 2D spectrometer have enabled the first 2D FT electronic spectroscopy in this wavelength range; we analyze the early time solvation dynamics of IR-26 dye. Agreement between experimental and simulated purely absorptive 2D spectra of this dye proves the feasibility of the spectrometer design. Accurate evolution time delays in the partially collinear geometry reduce ambiguities in the phasing of these 2D spectra. Finally, initial 2D spectra of lead chalcogenide quantum dots exhibit first exciton transition (bleach) peaks; weak negative peaks potentially reflect biexciton shifts. These spectra lay the groundwork for broadband 2D FT spectroscopy to find exciton couplings and dephasing rates to help establish the mechanism of carrier multiplication for high-efficiency photovoltaics. Advisors/Committee Members: David M. Jonas, Steven T. Cundiff, Niels H. Damrauer, Gordana Dukovic, Robert P. Parson.

Subjects/Keywords: Interferometry; Short-Wave Infrared; Two-Dimensional Spectroscopy; Optics; Physical Chemistry

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APA (6^th Edition):

Courtney, T. L. (2012). Bringing Two-Dimensional Fourier Transform Electronic Spectroscopy into the Short-Wave Infrared. (Doctoral Dissertation). University of Colorado. Retrieved from https://scholar.colorado.edu/chem_gradetds/69

Chicago Manual of Style (16^th Edition):

Courtney, Trevor Laurence. “Bringing Two-Dimensional Fourier Transform Electronic Spectroscopy into the Short-Wave Infrared.” 2012. Doctoral Dissertation, University of Colorado. Accessed April 13, 2021. https://scholar.colorado.edu/chem_gradetds/69.

MLA Handbook (7^th Edition):

Courtney, Trevor Laurence. “Bringing Two-Dimensional Fourier Transform Electronic Spectroscopy into the Short-Wave Infrared.” 2012. Web. 13 Apr 2021.

Vancouver:

Courtney TL. Bringing Two-Dimensional Fourier Transform Electronic Spectroscopy into the Short-Wave Infrared. [Internet] [Doctoral dissertation]. University of Colorado; 2012. [cited 2021 Apr 13]. Available from: https://scholar.colorado.edu/chem_gradetds/69.

Council of Science Editors:

Courtney TL. Bringing Two-Dimensional Fourier Transform Electronic Spectroscopy into the Short-Wave Infrared. [Doctoral Dissertation]. University of Colorado; 2012. Available from: https://scholar.colorado.edu/chem_gradetds/69

University of Colorado

7. Moody, Galan. Confinement Effects on the Electronic and Optical Properties of Semiconductor Quantum Dots Revealed with Two-Dimensional Coherent Spectroscopy.

Degree: PhD, Physics, 2013, University of Colorado

URL: https://scholar.colorado.edu/phys_gradetds/87

► Confinement of electron-hole pairs (excitons) in semiconductor quantum dots (QDs) leads to novel quantum phenomena, tunable optical properties and enhanced Coulomb interactions, all of… (more)

▼ Confinement of electron-hole pairs (excitons) in semiconductor quantum dots (QDs) leads to novel quantum phenomena, tunable optical properties and enhanced Coulomb interactions, all of which are sensitive to the size, shape and material composition of the QDs. This thesis discusses our pursuit in unraveling the complex interrelation between morphology of a QD and its electronic and optical properties. A series of epitaxially-grown semiconductor nanostructures with different QD sizes and composition is studied using optical two-dimensional coherent spectroscopy (2DCS). With the unique capabilities of unambiguously identifying coupling between resonances, isolating quantum pathways and revealing homogeneous dephasing information in heterogeneous systems, 2DCS is a powerful tool for studying QD ensembles. Of paramount importance is the exciton homogeneous line width, which is inversely proportional to the dephasing time. As the dephasing time sets the duration for which coherence is maintained, knowledge of the principal dephasing mechanisms in QDs is essential. 2D spectra of excitons in weakly-confining GaAs QDs reveal that elastic exciton-phonon coupling and intra-dot exciton-exciton interactions are responsible for line width broadening beyond the radiative limit, and the interaction strength of both mechanisms increases for decreasing QD size. These results are compared to those obtained from InAs QDs, which exhibit an order-of-magnitude larger confinement, to illustrate the role quantum confinement plays in exciton dephasing. The lowest energy optical transitions in semiconductor QDs are modified by confinement-enhanced Coulomb interactions, such as exchange-mediated coupling between excitons and correlation effects that can lead to bound and anti-bound states of two excitons. 2D spectra particularly sensitive to these interactions reveal that the electron and hole wave functions – and therefore the strength of Coulomb interactions – are sensitive to variations in QD size for the GaAs ensemble. In the InAs QDs, however, the wave functions are remarkably independent of the details of confinement, leading to similar electronic and optical properties for all QDs. To provide additional insight, the spectra are modeled using perturbative density matrix calculations, and the results are compared to many-body calculations to reveal the significance of the strength and nature of Coulomb interactions on the optical properties of QDs. Advisors/Committee Members: Steven T. Cundiff, David M. Jonas, Daniel S. Dessau, Andreas Becker, Markus B. Raschke.

Subjects/Keywords: Four-Wave Mixing; Multi-Dimensional Coherent Spectroscopy; Quantum Dots; Semiconductor Nanostructures; Ultrafast Coherent Spectroscopy; Physics

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APA (6^th Edition):

Moody, G. (2013). Confinement Effects on the Electronic and Optical Properties of Semiconductor Quantum Dots Revealed with Two-Dimensional Coherent Spectroscopy. (Doctoral Dissertation). University of Colorado. Retrieved from https://scholar.colorado.edu/phys_gradetds/87

Chicago Manual of Style (16^th Edition):

Moody, Galan. “Confinement Effects on the Electronic and Optical Properties of Semiconductor Quantum Dots Revealed with Two-Dimensional Coherent Spectroscopy.” 2013. Doctoral Dissertation, University of Colorado. Accessed April 13, 2021. https://scholar.colorado.edu/phys_gradetds/87.

MLA Handbook (7^th Edition):

Moody, Galan. “Confinement Effects on the Electronic and Optical Properties of Semiconductor Quantum Dots Revealed with Two-Dimensional Coherent Spectroscopy.” 2013. Web. 13 Apr 2021.

Vancouver:

Moody G. Confinement Effects on the Electronic and Optical Properties of Semiconductor Quantum Dots Revealed with Two-Dimensional Coherent Spectroscopy. [Internet] [Doctoral dissertation]. University of Colorado; 2013. [cited 2021 Apr 13]. Available from: https://scholar.colorado.edu/phys_gradetds/87.

Council of Science Editors:

Moody G. Confinement Effects on the Electronic and Optical Properties of Semiconductor Quantum Dots Revealed with Two-Dimensional Coherent Spectroscopy. [Doctoral Dissertation]. University of Colorado; 2013. Available from: https://scholar.colorado.edu/phys_gradetds/87

University of Colorado

8. Bohnet, Justin Gary. A Superradiant Laser and Spin Squeezed States: Collective Phenomena in a Rubidium Cavity QED System for Enhancing Precision Measurements.

Degree: PhD, Physics, 2014, University of Colorado

URL: https://scholar.colorado.edu/phys_gradetds/102

► By allowing a large ensemble of laser cooled and trapped ⁸⁷Rb atoms to interact collectively with an optical cavity, I have explored two phenomena… (more)

Subjects/Keywords: Cavity QED; Entanglement; Laser; Spin squeezing; Atomic, Molecular and Optical Physics; Optics

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APA (6^th Edition):

Bohnet, J. G. (2014). A Superradiant Laser and Spin Squeezed States: Collective Phenomena in a Rubidium Cavity QED System for Enhancing Precision Measurements. (Doctoral Dissertation). University of Colorado. Retrieved from https://scholar.colorado.edu/phys_gradetds/102

Chicago Manual of Style (16^th Edition):

Bohnet, Justin Gary. “A Superradiant Laser and Spin Squeezed States: Collective Phenomena in a Rubidium Cavity QED System for Enhancing Precision Measurements.” 2014. Doctoral Dissertation, University of Colorado. Accessed April 13, 2021. https://scholar.colorado.edu/phys_gradetds/102.

MLA Handbook (7^th Edition):

Bohnet, Justin Gary. “A Superradiant Laser and Spin Squeezed States: Collective Phenomena in a Rubidium Cavity QED System for Enhancing Precision Measurements.” 2014. Web. 13 Apr 2021.

Vancouver:

Bohnet JG. A Superradiant Laser and Spin Squeezed States: Collective Phenomena in a Rubidium Cavity QED System for Enhancing Precision Measurements. [Internet] [Doctoral dissertation]. University of Colorado; 2014. [cited 2021 Apr 13]. Available from: https://scholar.colorado.edu/phys_gradetds/102.

Council of Science Editors:

Bohnet JG. A Superradiant Laser and Spin Squeezed States: Collective Phenomena in a Rubidium Cavity QED System for Enhancing Precision Measurements. [Doctoral Dissertation]. University of Colorado; 2014. Available from: https://scholar.colorado.edu/phys_gradetds/102

University of Colorado

9. Singh, Rohan. Excitons in Semiconductor Quantum Wells Studied Using Two-Dimensional Coherent Spectroscopy.

Degree: PhD, Physics, 2015, University of Colorado

URL: https://scholar.colorado.edu/phys_gradetds/158

► Correlated electron-hole pairs, or excitons, in semiconductor nanostructures have been studied extensively over the past few decades. The optical response of excitons is complicated… (more)

▼ Correlated electron-hole pairs, or excitons, in semiconductor nanostructures have been studied extensively over the past few decades. The optical response of excitons is complicated due to inhomogeneous broadening, presence of multiple states, and exciton-exciton interactions. In this work we bring new perspectives to exciton physics in semiconductor quantum wells (QWs) through two-dimensional coherent spectroscopy (2DCS). The effect of QW growth direction on the optical properties of excitons is explored by studying (110)-oriented GaAs QWs. The homogeneous and inhomogeneous linewidths of the heavy-hole exciton resonance are measured. By probing the optical nonlinear response for polarization along the in-plane crystal axes [1-10] and [001], we measure different homogeneous linewidths for the two orthogonal directions. This difference is found to be due to anisotropic excitation-induced dephasing, caused by a crystal-axis-dependent absorption coefficient. The extrapolated zero-excitation density homogeneous linewidth exhibits an activation-like temperature dependence. Spectral diffusion of excitons in (001)-oriented QWs has been studied. We show that the spectral diffusion characteristics depend strongly on the sample temperature. Spectral diffusion is generally assumed to follow the strong-redistribution approximation, partly because of lack of any evidence to the contrary. We find that this assumption is violated at low sample temperatures for excitons in QWs; high-energy excitons preferentially relax due to a negligible phonon population at low temperatures. The frequency-frequency correlation function is measured through a numerical fitting procedure to quantify spectral diffusion for sample temperatures >20 K. Exciton-exciton interactions affect the light-matter interactions in QWs significantly. We present an intuitive and simple model for these interactions by treating excitons as interacting bosons. We show that the polarization-dependent exciton dephasing rate in GaAs quantum wells is due to the bosonic character of excitons. We fit slices from simulated spectra to those from the experimentally measured spectra and show that interference between two different quantum mechanical pathways results in a slower dephasing rate for co-circular and co-linear polarization of optical excitation pulses. This interference does not exist for cross-linearly polarized excitation pulses resulting in a faster dephasing rate. Additionally, we were able to separately quantify inter- and intra-mode interactions between excitons through exciton-density-dependent measurements. Advisors/Committee Members: Steven T. Cundiff, Markus B. Raschke, Daniel S. Dessau, Richard P. Mirin, Ralph Jimenez.

Subjects/Keywords: excitons; semiconductor nanostructures; decay processes; quantum well; interactions; excitation; Atomic, Molecular and Optical Physics; Quantum Physics

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APA (6^th Edition):

Singh, R. (2015). Excitons in Semiconductor Quantum Wells Studied Using Two-Dimensional Coherent Spectroscopy. (Doctoral Dissertation). University of Colorado. Retrieved from https://scholar.colorado.edu/phys_gradetds/158

Chicago Manual of Style (16^th Edition):

Singh, Rohan. “Excitons in Semiconductor Quantum Wells Studied Using Two-Dimensional Coherent Spectroscopy.” 2015. Doctoral Dissertation, University of Colorado. Accessed April 13, 2021. https://scholar.colorado.edu/phys_gradetds/158.

MLA Handbook (7^th Edition):

Singh, Rohan. “Excitons in Semiconductor Quantum Wells Studied Using Two-Dimensional Coherent Spectroscopy.” 2015. Web. 13 Apr 2021.

Vancouver:

Singh R. Excitons in Semiconductor Quantum Wells Studied Using Two-Dimensional Coherent Spectroscopy. [Internet] [Doctoral dissertation]. University of Colorado; 2015. [cited 2021 Apr 13]. Available from: https://scholar.colorado.edu/phys_gradetds/158.

Council of Science Editors:

Singh R. Excitons in Semiconductor Quantum Wells Studied Using Two-Dimensional Coherent Spectroscopy. [Doctoral Dissertation]. University of Colorado; 2015. Available from: https://scholar.colorado.edu/phys_gradetds/158

University of Colorado

10. Ni, Hongcheng. Theoretical Studies of Ultrafast Correlated Electron Dynamics in Single and Double Photoionization.

Degree: PhD, Physics, 2014, University of Colorado

URL: https://scholar.colorado.edu/phys_gradetds/112

► Recent advances in laser technology have led to the generation of attosecond laser pulses, whose duration is in the range of the natural time… (more)

▼ Recent advances in laser technology have led to the generation of attosecond laser pulses, whose duration is in the range of the natural time scale of electron dynamics, and thus make the observation and even control of electron dynamics in atoms and molecules possible. While the single-electron dynamics is more thoroughly studied, the correlated dynamics of two electrons is less understood, especially in the context of resolving the ultrafast temporal information in double photoionization. In this thesis, we first study the energy exchange via electron correlation upon photon absorption over large distances in the two-site double photoionization of the helium dimer, which is found to be a two-step process. In the first step, one electron in one atom absorbs the photon and gets ionized. In the second step, this electron propagates towards the neighboring atom and knocks out the other electron. We then introduce the Hamiltonian reduction method to further study the effects of different interactions in the single and double photoionization of the helium dimer. Next, we analyze the selection rules for the emission of two electrons from the helium atom, the helium dimer, and general molecules following the absorption of a few photons in an intense laser field. In particular, the back-to-back emission of the two electrons with equal energy sharing is either suppressed or not depending on the number of photons absorbed from the field. Finally, we study the time delay between the single and double photoionization processes. We first propose a self-consistent-time method to account for the Coulomb-laser coupling effect and obtain the intrinsic photoabsorption time delay measured by the attosecond streak camera. We then proceed to time resolve the correlated emission of two electrons in the knockout process of the helium dimer with respect to the first step of single ionization. Advisors/Committee Members: Andreas Becker, Margaret Murnane, Steven T. Cundiff, John L. Bohn, David Jonas.

Subjects/Keywords: attosecond laser; Hamiltonian reduction method; helium dimer; 4D model; coupling effect; selection rules; Atomic, Molecular and Optical Physics

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APA (6^th Edition):

Ni, H. (2014). Theoretical Studies of Ultrafast Correlated Electron Dynamics in Single and Double Photoionization. (Doctoral Dissertation). University of Colorado. Retrieved from https://scholar.colorado.edu/phys_gradetds/112

Chicago Manual of Style (16^th Edition):

Ni, Hongcheng. “Theoretical Studies of Ultrafast Correlated Electron Dynamics in Single and Double Photoionization.” 2014. Doctoral Dissertation, University of Colorado. Accessed April 13, 2021. https://scholar.colorado.edu/phys_gradetds/112.

MLA Handbook (7^th Edition):

Ni, Hongcheng. “Theoretical Studies of Ultrafast Correlated Electron Dynamics in Single and Double Photoionization.” 2014. Web. 13 Apr 2021.

Vancouver:

Ni H. Theoretical Studies of Ultrafast Correlated Electron Dynamics in Single and Double Photoionization. [Internet] [Doctoral dissertation]. University of Colorado; 2014. [cited 2021 Apr 13]. Available from: https://scholar.colorado.edu/phys_gradetds/112.

Council of Science Editors:

Ni H. Theoretical Studies of Ultrafast Correlated Electron Dynamics in Single and Double Photoionization. [Doctoral Dissertation]. University of Colorado; 2014. Available from: https://scholar.colorado.edu/phys_gradetds/112

University of Colorado

11. Tiwari, Vivek. Non-Adiabatic Mechanism for Photosynthetic Energy Transfer and All-Optical Determination of Concentration using Femtosecond Lasers.

Degree: PhD, Chemistry & Biochemistry, 2014, University of Colorado

URL: https://scholar.colorado.edu/chem_gradetds/122

► Development of efficient light-harvesting technologies hinges on our understanding of the fundamental physics of light-harvesting in both natural and artificial systems. This work addresses… (more)

▼ Development of efficient light-harvesting technologies hinges on our understanding of the fundamental physics of light-harvesting in both natural and artificial systems. This work addresses the following topics, i.) the mechanism underlying the remarkably efficient electronic energy transfer in natural light harvesting antennas, ii.) a femtosecond time-resolved photonumeric technique to quantitatively characterize transient chemical species. A non-adiabatic model for photosynthetic energy transfer in light harvesting antennas is proposed. Light harvesting antennas use a set of closely spaced pigment molecules held in a controlled relative geometry by a protein. It is shown that in the Fenna-Matthews-Olson (FMO) antenna protein, the antenna found in green sulfur bacteria, the excited state electronic energy gaps are resonant with a quantum of vibrational energy on its pigment, bacteriochlorophyll a. Through a dimer model loosely based on FMO, it is shown that such a resonance leads to an unavoidable nested non-adiabatic energy funnel on the excited states of photosynthetic antennas. The non-adiabatic model presented here leads to enhanced vibrational oscillations on the ground electronic state of these antennas, the 2D spectroscopic signatures and oscillation frequencies of which are consistent with all the reported 2D signatures of long-lived oscillations, including the ones that are not explained by prior models of excited state electronic energy transfer. Extensions that account for both resonant and near-resonant pigment vibrations suggest that photosynthetic energy transfer presents a novel design in which electronic energy transfer proceeds non-adiabatically through clusters of vibrations with frequencies distributed around electronic energy gaps. The latter part of the thesis presents absolute measurements of femtosecond pump-probe signal strength. The experiments demonstrate quantitative time-resolved measurement of absolute number of excited state molecules. Based on these measurements, an all-optical technique that simultaneously determines concentration and extinction coefficient of an unknown sample is presented. Unlike prior such analytical techniques, the present photonumeric method does not require any sample isolation, physical handling or in situ calibrant. In principle, the experimental and theoretical framework developed allows extensions towards characterization of transient chemical species. Advisors/Committee Members: David M. Jonas, Joel D. Eaves, Robert P. Parson, Steven T. Cundiff, Niels H. Damrauer.

Subjects/Keywords: 2D Spectroscopy; Absolute Pump-Probe; Exciton; Forster Resonance Energy Transfer; Photonumeric; Transient Chemical Species; Analytical Chemistry; Physical Chemistry

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APA (6^th Edition):

Tiwari, V. (2014). Non-Adiabatic Mechanism for Photosynthetic Energy Transfer and All-Optical Determination of Concentration using Femtosecond Lasers. (Doctoral Dissertation). University of Colorado. Retrieved from https://scholar.colorado.edu/chem_gradetds/122

Chicago Manual of Style (16^th Edition):

Tiwari, Vivek. “Non-Adiabatic Mechanism for Photosynthetic Energy Transfer and All-Optical Determination of Concentration using Femtosecond Lasers.” 2014. Doctoral Dissertation, University of Colorado. Accessed April 13, 2021. https://scholar.colorado.edu/chem_gradetds/122.

MLA Handbook (7^th Edition):

Tiwari, Vivek. “Non-Adiabatic Mechanism for Photosynthetic Energy Transfer and All-Optical Determination of Concentration using Femtosecond Lasers.” 2014. Web. 13 Apr 2021.

Vancouver:

Tiwari V. Non-Adiabatic Mechanism for Photosynthetic Energy Transfer and All-Optical Determination of Concentration using Femtosecond Lasers. [Internet] [Doctoral dissertation]. University of Colorado; 2014. [cited 2021 Apr 13]. Available from: https://scholar.colorado.edu/chem_gradetds/122.

Council of Science Editors:

Tiwari V. Non-Adiabatic Mechanism for Photosynthetic Energy Transfer and All-Optical Determination of Concentration using Femtosecond Lasers. [Doctoral Dissertation]. University of Colorado; 2014. Available from: https://scholar.colorado.edu/chem_gradetds/122

University of Colorado

12. Baker, Thomas Athanasius. Confocal Microscopy Studies of Fluorescence Blinking of Semiconductor Quantum Dots, Metal Nanoparticle Photogeneration, and Multiphoton Photoemission from Thin Metal Films and Metal Nanoparticles.

Degree: PhD, Chemistry & Biochemistry, 2012, University of Colorado

URL: https://scholar.colorado.edu/chem_gradetds/127

► Since the advent of single molecule spectroscopy in 1989, advances in the field have revealed a wealth of information on dynamics and sample heterogeneity… (more)

▼ Since the advent of single molecule spectroscopy in 1989, advances in the field have revealed a wealth of information on dynamics and sample heterogeneity unobtainable by traditional ensemble studies. Microscopy experiments are a common technique to characterize and probe single molecule dynamics, due to the combination of the diffraction limited spatial resolution and the availability of sensitive single photon/electron detectors. Additionally, high excitation power densities can be achieved by the use of large numerical aperture objectives with moderately intense light sources. Fluorescence intermittency, or blinking, is a unique property found in the emission of single molecules. A series of experiments are undertaken to elucidate contributions to the blinking dynamics in nanocrystal semiconductors, or quantum dots (QDs). Investigations of the transitions from "on" to "off" (and vice versa) in the absence of laser illumination allow for the determination of the roles of light versus non-light induced processes for single blinking QDs. Small molecules are found to influence QD blinking by altering the surface trap state distribution due to changes in the electrochemical potential of the solution. However, fluorescence detection is only one implementation to investigate single molecule systems by microscopy. Nanoscale metal materials possess many interesting electronic and optical properties that enable single molecule or particle detection. Silver and gold metal nanoparticles are of particular interest due to their surface plasmon resonances (SPRs), a collective electron oscillation excited in the near ultraviolet and visible range. As a result of the coherent electron oscillations on the surface of the particle, large electric fields are generated in the vicinity of the nanostructure. This local enhancement of the electric field enables molecular detection in the vicinity of particles by surface-enhanced Raman scattering (SERS). One difficulty with conventional systems used to study SERS is the large enhancement variability observed between nanoparticles on the same substrate, where typically only 1 in 100-1000 are found to have the necessary enhancement factors. Photogeneration of Ag nanoparticles within a thin silver percholorate/polystyrene polymer film form reproducible SERS active nanoparticles that can be monitored and characterized by Raman microscopy. Insight into the growth mechanism of the nanoparticles is provided by analysis of the time dependent data with an Avrami kinetic phase transformation model. The environment in which the nanoparticles are generated is found to influence both the photogeneration kinetics and the nanoparticles SERS activity. Information on the size and morphology of the nanoparticles provided by AFM and dark field scattering measurements allowing for correlation of photophysical properties with nanoparticle shape. Lastly, the electric field enhancements, exploited by SERS in the Ag nanoparticle system, are investigated for Au single nanoparticles by… Advisors/Committee Members: David J. Nesbitt, Steven T. Cundiff, Mathias Weber, Veronica Bierbaum, Eric Cornell.

Subjects/Keywords: blinking; plasmon; quantum dot; SERS; Physical Chemistry

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

Baker, T. A. (2012). Confocal Microscopy Studies of Fluorescence Blinking of Semiconductor Quantum Dots, Metal Nanoparticle Photogeneration, and Multiphoton Photoemission from Thin Metal Films and Metal Nanoparticles. (Doctoral Dissertation). University of Colorado. Retrieved from https://scholar.colorado.edu/chem_gradetds/127

Chicago Manual of Style (16^th Edition):

Baker, Thomas Athanasius. “Confocal Microscopy Studies of Fluorescence Blinking of Semiconductor Quantum Dots, Metal Nanoparticle Photogeneration, and Multiphoton Photoemission from Thin Metal Films and Metal Nanoparticles.” 2012. Doctoral Dissertation, University of Colorado. Accessed April 13, 2021. https://scholar.colorado.edu/chem_gradetds/127.

MLA Handbook (7^th Edition):

Baker, Thomas Athanasius. “Confocal Microscopy Studies of Fluorescence Blinking of Semiconductor Quantum Dots, Metal Nanoparticle Photogeneration, and Multiphoton Photoemission from Thin Metal Films and Metal Nanoparticles.” 2012. Web. 13 Apr 2021.

Vancouver:

Baker TA. Confocal Microscopy Studies of Fluorescence Blinking of Semiconductor Quantum Dots, Metal Nanoparticle Photogeneration, and Multiphoton Photoemission from Thin Metal Films and Metal Nanoparticles. [Internet] [Doctoral dissertation]. University of Colorado; 2012. [cited 2021 Apr 13]. Available from: https://scholar.colorado.edu/chem_gradetds/127.

Council of Science Editors:

Baker TA. Confocal Microscopy Studies of Fluorescence Blinking of Semiconductor Quantum Dots, Metal Nanoparticle Photogeneration, and Multiphoton Photoemission from Thin Metal Films and Metal Nanoparticles. [Doctoral Dissertation]. University of Colorado; 2012. Available from: https://scholar.colorado.edu/chem_gradetds/127

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