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You searched for subject:(Gradient Index Lenses). Showing records 1 – 3 of 3 total matches.

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University of Rochester

1. Gandara-Montano, Gustavo A. Advances in deterministic femtosecond laser writing of vision correction devices in ophthalmic hydrogels.

Degree: PhD, 2019, University of Rochester

Femtosecond laser writing can be used to generate a spatially varying refractive index profile within a material, which results in the creation of a gradient-index (GRIN) lens. Creating GRIN lenses in hydrogels via femtosecond laser writing can enable visual correction applications in contact lenses and in intraocular lenses (IOLs) that are currently impossible or impractical to achieve. These potential applications include the creation of visual correctors with higher-order corrections, the imprinting of the wavefront correction in an already implanted IOL, and the ability to further customize a lens already having a femtosecond laser-written correction written in it, among several others. To further advance the field of femtosecond laser writing of visual correctors, this thesis concerns itself with demonstrating the ability of femtosecond laser writing to create high-quality vision correctors in ophthalmic hydrogels. To do so, first we present an interferometric technique that measures the “calibration function”, which is the phase induced in the wavefront when passing through a femtosecond laser-written region as a function of the exposure parameters applied when writing such region. Knowledge of the calibration function allows for the writing of the desired wavefront, as we demonstrated by the creation of arbitrary freeform structures with diameters of 150 μm in commercially available contact lenses. The writing of lenses of clinically relevant size in plano hydrogels made of an ophthalmic material was achieved by writing different sections of the lens separately and stitching them together. Metrology on the stitched lenses indicates good optical and imaging performance. However, diffraction streaks created by the stitching grid were observed, as well as some unintended multifocality, which was attributed to the induced phase evolving in time after the writing. Furthermore, the visual performance of participants looking through one of the stitched GRIN lenses was measured to be quite good. Moreover, for the desired correction to be written quickly, it is necessary to use a writing material in which large phase shifts can be induced at large scanning speeds and with the available laser power. In this thesis, we measured the induced phase on several materials and under several writing conditions, and we report the finding of chemical compositions that yielded multiple waves of phase change (at the center of the visible spectrum) at a writing speed of 100 mm/s. Raman spectroscopy measurements of the written areas in the sample indicate that they have a higher water concentration than the surrounding unwritten areas. This work demonstrates the capability of femtosecond laser writing to produce high quality visual correctors, as well as introducing chemical compositions of ophthalmic materials that can be used for a faster writing process.

Subjects/Keywords: Femtosecond phenomena; Gradient-index lenses; Ophthalmic appliances; Polymers

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

APA (6th Edition):

Gandara-Montano, G. A. (2019). Advances in deterministic femtosecond laser writing of vision correction devices in ophthalmic hydrogels. (Doctoral Dissertation). University of Rochester. Retrieved from http://hdl.handle.net/1802/35054

Chicago Manual of Style (16th Edition):

Gandara-Montano, Gustavo A. “Advances in deterministic femtosecond laser writing of vision correction devices in ophthalmic hydrogels.” 2019. Doctoral Dissertation, University of Rochester. Accessed May 09, 2021. http://hdl.handle.net/1802/35054.

MLA Handbook (7th Edition):

Gandara-Montano, Gustavo A. “Advances in deterministic femtosecond laser writing of vision correction devices in ophthalmic hydrogels.” 2019. Web. 09 May 2021.

Vancouver:

Gandara-Montano GA. Advances in deterministic femtosecond laser writing of vision correction devices in ophthalmic hydrogels. [Internet] [Doctoral dissertation]. University of Rochester; 2019. [cited 2021 May 09]. Available from: http://hdl.handle.net/1802/35054.

Council of Science Editors:

Gandara-Montano GA. Advances in deterministic femtosecond laser writing of vision correction devices in ophthalmic hydrogels. [Doctoral Dissertation]. University of Rochester; 2019. Available from: http://hdl.handle.net/1802/35054


Penn State University

2. Brocker, Donovan Edward. EFFICIENT OPTIMIZATION OF ANTENNA AND ELECTROMAGNETIC DEVICES AT MEDIUM, RADIO, AND OPTICAL FREQUENCIES.

Degree: 2016, Penn State University

The fast growth of computer technology has led to aggressive advancement in engineering design, where in the past, analytical methods and/or intuitive trial and error through experiments were the most lucrative tools. Specifically in electromagnetics, powerful computers can be used to run simulation models subject to numerical solutions of Maxwell’s equations, providing extremely accurate predictions of the device performance. Growing computer resources also offer the ability to optimize devices via simulation, facilitating fine-tuning before fabrication. Hence, engineering design has drifted more and more towards computer modeling and optimization and has, in some cases, drifted away from intuition-based design and experimental fine-tuning. Although the former approach has the tendency to lower research and development costs and, at times, predict novel devices, the latter is still essential to the overall advancement of engineering design. With this in mind, this dissertation summarizes multiple efforts, ranging across many sub-fields of electromagnetics, where computer modeling and optimization was strongly coupled to intuitive design. This approach leads to efficient optimization of high performance designs that would likely not be possible with analytical or brute-force computer optimization alone. First, a hybrid approach combining transmission line equations and full-wave models is developed to optimize large communication networks in coal mines for emergency response applications. Secondly, a miniaturized dual-band antenna with an interdigitated slot load is proposed based on transmission line models and fine-tuned using computer simulation models. The antenna was fabricated and characterized, showing excellent agreement with simulation predictions. Next, an ultra-thin electromagnetic absorber design is proposed based on an equivalent circuit model. In particular, the circuit model is used to optimize the absorber design for wide bandwidth. Subsequently, the circuit model is used to simplify the optimization routine by cascading the scattering properties of the different absorber regions. Finally, gradient-index lens design methodology is developed based on transformation optics, enabling superior mono- and polychromatic lens performances. Advisors/Committee Members: Douglas Henry Werner, Dissertation Advisor/Co-Advisor, Douglas Henry Werner, Committee Chair/Co-Chair, Ram Mohan Narayanan, Committee Member, Timothy Joseph Kane, Committee Member, Douglas Edward Wolfe, Outside Member.

Subjects/Keywords: Antennas; Coal Mine Communications; Electromagnetic Absorbers; Gradient-Index Lenses; Transformation Optics

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

APA (6th Edition):

Brocker, D. E. (2016). EFFICIENT OPTIMIZATION OF ANTENNA AND ELECTROMAGNETIC DEVICES AT MEDIUM, RADIO, AND OPTICAL FREQUENCIES. (Thesis). Penn State University. Retrieved from https://submit-etda.libraries.psu.edu/catalog/2f75r800t

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16th Edition):

Brocker, Donovan Edward. “EFFICIENT OPTIMIZATION OF ANTENNA AND ELECTROMAGNETIC DEVICES AT MEDIUM, RADIO, AND OPTICAL FREQUENCIES.” 2016. Thesis, Penn State University. Accessed May 09, 2021. https://submit-etda.libraries.psu.edu/catalog/2f75r800t.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7th Edition):

Brocker, Donovan Edward. “EFFICIENT OPTIMIZATION OF ANTENNA AND ELECTROMAGNETIC DEVICES AT MEDIUM, RADIO, AND OPTICAL FREQUENCIES.” 2016. Web. 09 May 2021.

Vancouver:

Brocker DE. EFFICIENT OPTIMIZATION OF ANTENNA AND ELECTROMAGNETIC DEVICES AT MEDIUM, RADIO, AND OPTICAL FREQUENCIES. [Internet] [Thesis]. Penn State University; 2016. [cited 2021 May 09]. Available from: https://submit-etda.libraries.psu.edu/catalog/2f75r800t.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Brocker DE. EFFICIENT OPTIMIZATION OF ANTENNA AND ELECTROMAGNETIC DEVICES AT MEDIUM, RADIO, AND OPTICAL FREQUENCIES. [Thesis]. Penn State University; 2016. Available from: https://submit-etda.libraries.psu.edu/catalog/2f75r800t

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

3. Cebrecos Ruiz, Alejandro. Transmission, reflection and absorption in Sonic and Phononic Crystals .

Degree: 2015, Universitat Politècnica de València

[EN] Phononic crystals are artificial materials formed by a periodic arrangement of inclusions embedded into a host medium, where each of them can be solid or fluid. By controlling the geometry and the impedance contrast of its constituent materials, one can control the dispersive properties of waves, giving rise to a huge variety of interesting and fundamental phenomena in the context of wave propagation. When a propagating wave encounters a medium with different physical properties it can be transmitted and reflected in lossless media, but also absorbed if dissipation is taken into account. These fundamental phenomena have been classically explained in the context of homogeneous media, but it has been a subject of increasing interest in the context of periodic structures in recent years as well. This thesis is devoted to the study of different effects found in sonic and phononic crystals associated with transmission, reflection and absorption of waves, as well as the development of a technique for the characterization of its dispersive properties, described by the band structure. We start discussing the control of wave propagation in transmission in conservative systems. Specifically, our interest is to show how sonic crystals can modify the spatial dispersion of propagating waves leading to control the diffractive broadening of sound beams. Making use of the spatial dispersion curves extracted from the analysis of the band structure, we first predict zero and negative diffraction of waves at frequencies close to the band-edge, resulting in collimation and focusing of sound beams in and behind a 3D sonic crystal, and later demonstrate it through experimental measurements. The focusing efficiency of a 3D sonic crystal is limited due to the strong scattering inside the crystal, characteristic of the diffraction regime. To overcome this limitation we consider axisymmetric structures working in the long wavelength regime, as a gradient index lens. In this regime, the scattering is strongly reduced and, in an axisymmetric configuration, the symmetry matching with acoustic sources radiating sound beams increase its efficiency dramatically. Moreover, the homogenization theory can be used to model the structure as an effective medium with effective physical properties, allowing the study of the wave front profile in terms of refraction. We will show the model, design and characterization of an efficient focusing device based on these concepts. Consider now a periodic structure in which one of the parameters of the lattice, such as the lattice constant or the filling fraction, gradually changes along the propagation direction. Chirped crystals represent this concept and are used here to demonstrate a novel mechanism of sound wave enhancement based on a phenomenon known as "soft" reflection. The enhancement is related to a progressive slowing down of the wave as it propagates along the material, which is associated with the group velocity of the local dispersion relation at the planes of the crystal. A model based on the… Advisors/Committee Members: Picó Vila, Rubén (advisor), Sánchez Morcillo, Víctor José (advisor).

Subjects/Keywords: Periodic Structures; Sonic Crystals, Phononic Crystals; Transmission; Reflection, Absorption; Band Structure; Dispersion Relation; Focusing; Focalization; Collimation; Spatial dispersion; Beam; Acoustic Beam; Ultrasonic Beam; Axisymmetric; Symmetry Matching; Gradient Index; Lens; Lenses; Homogenization; Refraction; Refractive devices; Long-wavelength; Effective medium; Effective properties; Paraxial approximation; Isofrequency lines; Isofrequency contours; Wave vector; Chirped; Tappered; Rainbow trapping; Mirage effect; Chirped crystals; Wave Enhancement; Soft reflection; Group velocity; Slowing down; Coupled Mode Theory; CMT; Linear Chirped; Exponential chirped; Dissipation; Losses; Porous absorber; Porous material; Porous layers; Dissipative couple mode theory; Modulation; Loss modulation; Band structure calculation; Elastic waves; Acoustic waves; Time-marching; Algorithm; Bloch vector; Bloch boundary conditions; Boundary conditions; Unit cell; Vibrational modes; Resonant peaks; Resonant modes; Accuracy; Convergence; Computation time; Solid-Solid; Solid-fluid; Lamella cyrstal; Extraordinary absorption; Interaction strength; Time delay; Fourier Transform

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

APA (6th Edition):

Cebrecos Ruiz, A. (2015). Transmission, reflection and absorption in Sonic and Phononic Crystals . (Doctoral Dissertation). Universitat Politècnica de València. Retrieved from http://hdl.handle.net/10251/56463

Chicago Manual of Style (16th Edition):

Cebrecos Ruiz, Alejandro. “Transmission, reflection and absorption in Sonic and Phononic Crystals .” 2015. Doctoral Dissertation, Universitat Politècnica de València. Accessed May 09, 2021. http://hdl.handle.net/10251/56463.

MLA Handbook (7th Edition):

Cebrecos Ruiz, Alejandro. “Transmission, reflection and absorption in Sonic and Phononic Crystals .” 2015. Web. 09 May 2021.

Vancouver:

Cebrecos Ruiz A. Transmission, reflection and absorption in Sonic and Phononic Crystals . [Internet] [Doctoral dissertation]. Universitat Politècnica de València; 2015. [cited 2021 May 09]. Available from: http://hdl.handle.net/10251/56463.

Council of Science Editors:

Cebrecos Ruiz A. Transmission, reflection and absorption in Sonic and Phononic Crystals . [Doctoral Dissertation]. Universitat Politècnica de València; 2015. Available from: http://hdl.handle.net/10251/56463

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