<p> Rare-earth-doped fiber lasers and amplifiers are relatively easy to efficiently produce a stable and high quality laser beam in a compact, robust, and alignment-free configuration. Recently, high power fiber laser systems have facilitated wide spread applications in academics, industries, and militaries in replacement of bulk solid-state laser systems. The master oscillator power amplifier (MOPA) composed of a highly-controlled seed, high-gain preamplifiers, and high-efficiency power amplifiers are typically utilized to scale up the pulse energy, peak power, or average power. Furthermore, a direct-current-modulated nanosecond diode laser in single transverse mode can simply provide a compact and highly-controlled seed to result in the flexible output parameters, such as repetition rate, pulse duration, and even temporal pulse shape. However, when scaling up the peak power for high intensity applications, such a versatile diode-seeded nanosecond MOPA laser system using rare-earth-doped fibers is unable to completely save its own advantages compared to bulk laser systems. Without a strong seeding among the amplifiers, the guided amplified spontaneous amplification is easy to become dominant during the amplification, leading to the harmful self-lasing or pulsing effects, and the difficulty of the quantitative numerical comparison. In this dissertation, we study a high-efficiency and intense nanosecond ytterbium fiber MOPA system with good beam quality and stability for high intensity applications. The all-PM-fiber structure is achieved with the output extinction ratio of >12 dB by optimizing the interconnection of high power optical fibers.</p><p> The diode-seeded MOPA configuration without parasitic stimulated amplification (PAS) is implemented using the double-pass scheme to extract energy efficiently for scaling peak power. The broadband PAS was studied experimentally, which matches well with our numerical simulation. The 1064-nm nanosecond seed was a direct-current-modulated Fabry-P&eacute;rot diode laser associated with a weak and pulsed noise spanning from 1045 to 1063 nm. Even though the contribution of input noise pulse is only &lt;5%, it becomes a significant transient spike during amplification. The blue-shifted pulsed noise may be caused by band filling effect for quantum-well seed laser driven by high peak current. The study helps the development of adaptive pulse shaping for scaling peak power or energy at high efficiency. On the other hand, the broadband spike with a 3-dB bandwidth of 8.8 nm can support pulses to seed the amplifier for sub-nanosecond giant pulse generation.</p><p> Because of the very weak seed laser, the design of high-gain preamplifier becomes critical. The utilization of single-mode core-pumped fiber preamplifier can not only improve the mode contrast without fiber coiling effect but also significantly suppress the fiber nonlinearity. The double-pass scheme was therefore studied both numerically and experimentally to improve energy extraction efficiency for the lack of attainable seed and core-pumped power. As a result, a record-high peak power of > 30 kW and energy of > 0.23 mJ was successfully achieved to the best of our knowledge from the output of clad-pumped power amplifier with a beam quality of M² &sim;1.1 in a diode-seeded 15-&micro;m-core fiber MOPA system. After the power amplifier, the MOPA conversion efficiency can be dramatically improved to >56% for an energy gain of >63 dB at a moderate repetition rate of 20 kHz with a beam quality of M² &lt;1.5. The output energy of >1.1 mJ with a pulse duration of &sim;6.1 ns can result in a peak power up to >116 kW which is limited by fiber fuse in long-term operation. Such a condition able to generate the on-target laser intensity of > 60 GW/cm² for applications is qualified to preliminarily create a laser-plasma light source. Moreover, the related simulation results also reveal the double-passed power amplifier can further simplify MOPA.</p><p> Such an intense clad-pumped power amplifier can further become a nonlinear fiber amplifier in all-normal dispersion instead of a nonlinear passive fiber. The combination of laser amplification and nonlinear conversion together can therefore overcome the significant pump depletion during the propagation along the passive fiber for power scaling. As a result, an intense spectrum spanning from 980 to 1600 nm as a high-power nanosecond supercontinuum source can be successfully generated with a conversion efficiency of >65% and a record-high peak power of >116 kW to the best of our knowledge. Because of MOPA structure, the influence of input parameters of nonlinear fiber amplifier on supercontinuum parameters can also be studied. The onset and interplay of fiber nonlinearities can be revealed stage by stage. Such an unique and linearly-polarized light source composed of an intense pump and broad sideband seed is beneficial for efficiently driving the broadband tunable optical parametric amplification free from the bulkiness and timing jitter.</p><p> Keywords: High power fiber laser and amplifier, ytterbium fiber, master oscillator power amplification, parasitic stimulated amplification, multi-pass fiber amplification, peak power/pulse energy scaling, fiber nonlinear optics, supercontinuum generation.</p>

<p> In addition to the display application, Liquid Crystals (LC) can be very useful in other applications such as beam steering, tunable lenses, etc. </p><p> Electro-optical LC tunable lenses have been considered as an alternative to conventional glass lenses because of their ability to change their focal length with the application of a control voltage, as well as small size and weight and low power consumption, fast speed, etc. They have a great potential in many applications such as: imaging systems of compact cameras, eye correction, and 3D display systems. So far, while many LC lens designs have been published, high quality performance has been only mentioned in very few papers; also, the level of details in those work is less than what is required to have an accurate evaluation of the performance as well as how it could be improved. </p><p> Therefore, the main goal of the work in this dissertation is designing high quality or near diffraction limited LC tunable lenses. We will not only introduce our design concepts and considerations, but also demonstrate fine details about the fabrication and evaluations. More importantly, we will use both simulation and experimental approaches for fully understanding the fundamental limiting factors affecting LC lenses. Consequently, we will introduce how they could be optimized and demonstrate the improved performance. In addition, there will be work addressing the concerns about speed, optical power, and off-axis performance. </p><p> The outline of the dissertation is given as follows, and each chapter has its own focus: In chapter 2, we will review the background of tunable LC lenses, introduce our design, and evaluate its performance in details; in chapter 3, we will investigate the physical limitations and fundamental factors affecting LC lens performance with both simulation and experimental results; in chapter 4, we will introduce the optimized design and demonstrate the improved performance; in chapter 5, we will introduce a multi-cell approach to improve its off-axis imaging performance and achieve a higher optical power, while keeping the fast switching speed; in chapter 6, we will discuss the phase reset methods to achieve higher optical power and fast response; finally in the last chapter, we will make the conclusion and summary. Also, there are four appendices in which we show the detailed LC lens fabrication process, complete optical characterization methods, simulation methods used in this dissertation work and the core Matlab codes, respectively.</p>

<p> This dissertation describes the design, development, and field validation of a concentrator photovoltaic (CPV) solar energy system. The challenges of creating a highly efficient yet low-cost system architecture come from many sources. The solid-state physics of photovoltaic devices present fundamental limits to photoelectron conversion efficiency, while the electrical and thermal characteristics of widely available materials limit the design arena. Furthermore, the need for high solar spectral throughput, evenly concentrated sunlight, and tolerance to off-axis pointing places strict illumination requirements on the optical design. To be commercially viable, the cost associated with all components must be minimized so that when taken together, the absolute installed cost of the system in kWh is lower than any other solar energy method, and competitive with fossil fuel power generation. </p><p> The work detailed herein focuses specifically on unique optical design and illumination concepts discovered when developing a viable commercial CPV system. By designing from the ground up with the fundamental physics of photovoltaic devices and the required system tolerances in mind, a select range of optical designs are determined and modeled. Component cost analysis, assembly effort, and development time frame further influence design choices to arrive at a final optical system design. </p><p> When coupled with the collecting mirror, the final optical hardware unit placed at the focus generates more than 800W, yet is small and lightweight enough to hold in your hand. After fabrication and installation, the completed system's illumination, spectral, and thermal performance is validated with on-sun operational testing.</p>

<p> Aero-optical distortions are detrimental to airborne optical systems. To study distortion mechanisms, compressible large-eddy simulations are performed for a Mach 0.5 turbulent boundary layer and a separated shear layer over a cylindrical turret with and without passive control in the upstream boundary layer. Optical analysis is carried out using ray tracing based on the computed density field and Gladstone-Dale relation.</p><p> In the flat-plate boundary layer, the effects of aperture size, Reynolds number, small-scale turbulence, different flow regions and beam elevation angle are examined, and the underlying flow physics is analyzed. Three momemtum-thickness Reynolds numbers, <i>Re</i>_&thetas; = 875, 1770 and 3550, are considered. It is found that the level of optical distortions decreases with increasing Reynolds number within the Reynolds number range considered. The contributions from the viscous sublayer and buffer layer are small, while the wake region plays a dominant role followed by the logarithmic layer. By low-pass filtering the fluctuating density field, it is shown that small-scale turbulence is optically inactive. Consistent with previous experimental findings, the distortion magnitude is dependent on the propagation direction due to anisotropy of the boundary-layer vortical structures. Density correlations and length scales are analyzed to understand the elevation-angle dependence and its relation to turbulence structures. The applicability of Sutton's linking equation to boundary-layer flows is examined, and excellent agreement between linking equation predictions and directly integrated distortions is obtained when the density length scale is appropriately defined.</p><p> The second case studied involves a separated shear layer over a cylindrical turret with a flat window, with inflow from a flat-plate boundary layer with and without passive control devices. The flow and optical results show reasonable agreement with experimental data for the baseline case without control. Aperture size effect, frequency spectra of OPD and two-point spatial correlations of OPD are investigated. The similarities and differences of distortion characteristics compared to those induced by turbulent boundary layers are discussed. The distortions by a separated shear layer are much larger in magnitude and spatially less homogeneous than those induced by an attached boundary layer. It is found that pressure fluctuations are significant and play a dominant role in inducing density fluctuations and associated optical distortions in a separated shear layer, in contrast to the dominant role of temperature fluctuations in a turbulent boundary layer. When passive control is applied using a row of thin and tall pins in the upstream boundary layer, the numerical results confirm key experimental findings. The flow above the optical window is characterized by two distinct shear layers, whose combined effect leads to a significant reduction of density fluctuation magnitude in the main shear layer and associated optical distortions compared to the uncontrolled flow with a single strong shear layer.</p>

<p> High-speed photodiodes have diverse applications in wireless and fiber communications. They can be used as output stages for antenna systems as well as receivers for fiber optic networks. Silicon is an attractive substrate material for photonic components for a number of reasons. Low cost manufacturing in CMOS fabrication facilities, low material loss at telecommunications wavelengths, and relatively simple co-packaging with electronics are all driving interest in silicon photonic devices. Since silicon does not absorb light at telecommunications wavelengths, photodetector fabrication requires the integration of either III-V materials or germanium. Recent work on germanium photodetectors has focused on low-capacitance devices suitable for integration with silicon electronics. These devices have excellent bandwidth and efficiency, but have not been designed for the levels of photocurrent required by coherent and analog systems. This thesis explores the design, fabrication, and measurement of photodetectors fabricated on silicon with germanium absorbing regions for high speed and high power performance. </p><p> There are numerous design trade-offs between speed, efficiency, and output power. Designing for high bandwidth favors small devices for low capacitance. Small devices require abrupt absorption profiles for good efficiency, but design for high output power favors large devices with dilute absorption. The absorption profile can be controlled by the absorber layer thickness, but this will also affect the bandwidth and power handling. This work quantifies the trade-offs between high speed, high efficiency, and high power design. Intrinsic region thickness and absorption profile are identified as the most important design variables. For PIN structures, the absorption profile and intrinsic region thickness are both functions of the Ge thickness, but in uni-traveling carrier (UTC) structures the absorption profile and intrinsic region can be designed independently. This allows optimization of the absorption profile independently from the RC-limited frequency response and compression current and ultimately enables larger saturation current-bandwidth products. This thesis includes the first theory, fabrication, and measurement of a uni-traveling carrier photodiode on the Si/Ge platform. Key contributions include an accurate nonlinear device model and a complete set of processes and design rules for fabricating Ge devices in the UCSB nanofab. The UTC structure is shown to be useful in extending the bandwidth and power handling capabilities of waveguide-integrated photodiodes, especially at high frequencies.</p>

<p> The objective in this thesis is to study the structure of peptides using molecular spectroscopy. Molecular spectroscopy, both vibrational and electronic, can be used as a sensitive tool to study molecular structure. Since it is an inherently low resolution method, theoretical calculations are essential for a complete understanding of vibrational and electronic spectra. The first part of this thesis contains quantum chemical calculations of the molecular spectra of several small peptide systems with different secondary structures. Optical trapping is a method that allows for the manipulation of sub-micron scale objects using tightly focused laser light. Raman spectroscopy, which is sensitive to molecular vibrations also requires intense laser light. Combined with optical tweezing, Raman spectroscopy can prove to be a very powerful tool to study small sample volumes and probe single living cells. In the second part of this thesis, I detail the construction an such an instrument, an optical trapping Raman spectrometer (OTRS). Our OTRS can measure Raman spectra from sub micron systems while at the same time quantifying the mechanical forces that are acting upon them. Thus the OTRS can give insight into the relationship between mechanical forces acting upon cells and their molecular structure. </p>

<p>Micro-electro-mechanical systems deformable-membrane mirrors provide a means of focus control and attendant spherical aberration correction for miniaturized imaging systems. The technology has greatly advanced in the last decade, thereby extending their focal range capabilities. This dissertation describes a novel SU-8 2002 silicon-on-insulator wafer deformable mirror. A 4.000 mm x 5.657 mm mirror for 45o incident light rays achieves 22 &#61549;m stroke or 65 diopters, limited by snapdown. The mirrors show excellent optical quality while flat. Most have peak-to-valley difference of less than 150 nm and root-mean-square less than 25 nm. The process proves simple, only requiring a silicon-on-insulator wafer, SU-8 2002, and a metal layer. Xenon difluoride etches the silicon to release the mirrors. Greater than 90% of the devices survive fabrication and release. While current literature includes several aberration analyses on static mirrors, analyses that incorporate the dynamic nature of these mirrors do not exist. Optical designers may have a choice between deformable mirrors and other types of varifocal mirrors or lenses. Furthermore, a dynamic mirror at an incidence angle other than normal may be desired due to space limitations or for higher throughput (normal incidence requires a beam splitter). This dissertation presents an analysis based on the characteristic function of the system. It provides 2nd and 3rd order aberration coefficients in terms of dynamic focus range and base ray incidence angle. These afford an understanding of the significance of different types of aberrations. Root-mean-square and Strehl calculations provide insight into overall imaging performance for various conditions. I present general guidelines for maximum incidence angle and field of fiew that provide near diffraction-limited performance. Experimental verification of the MEMS mirrors at 5o and 45o incidence angles validates the analytical results. A Blu-ray optical pick-up imaging demonstration shows the utility of these mirrors for focus control and spherical aberration correction. Imaging results of the first demonstration of a deformable mirror for dynamic agile focus control and spherical aberration correction in a commercial table-top confocal microscope are also shown.

This thesis discusses the development, characterisation and evaluation of a compact, medium power, XeCl laser operating at pulse repetition frequencies (prf) >1kHz. The use of this laser to cut polymer films by ablative etching is also presented. The device uses a closed-cycle gas flow loop, constructed from stainless-steel for corrosive gas compatibility, and a total volume of 6 litres and a working pressure of 4 atmospheres. A magnetically coupled, tangential fan provides the gas flow and, with appropriate flow shaping into the 0.8 x 1.5 x 22.0cm⁻³ discharge region, produces a maximum flow velocity of 40m.s⁻¹. Electrical excitation is provided by a conventional, thyratron switched, capacitor discharge circuit, coupled with an internal, capacitively loaded, uv spark preionisation scheme, resulting in a rapid energy deposition into the discharge. Investigations of the effects of discharge perturbations on the maximum repetition rate capability of this laser, Indicate that repetition rates up to 1800Hz should be feasible. In operation, the laser has proven to be capable of 16W at 1kHz, and 22W at 700Hz, with a 10nF charging capacitor. Qualitative studies of the effect of resonator configuration on the beam profile, have shown that the use of folded cavities will produce more uniform beam profiles. Experiments have been carried out, using this laser, to cut thin polyethylene teraphthalate (PET) film at rates up to 1.3m.s⁻¹. The 8x15mm output beam from the laser, was brought to a 5.4mm long line-focus with a full width of 140µm. It is shown that the effective etch rate, and corresponding cutting efficiency, is markedly dependent on prf due, it Is thought, to cumulative heating.

No description available.

<p> Over the last two decades, a large number of exoplanets have been confirmed with the rate of discovery increasing in recent years primarily as new instruments with improved sensitivities have become available. Direct imaging of an Earth-like planet is now an important goal of the science community. This is a challenging problem for two primary reasons. First, the intensity ratio between the bright star and its dim Earth-like companion is expected to be approximately ten orders of magnitude and, second, the angular separation to the star is very small. </p><p> An external occulter is a specially-shaped spacecraft that is flown in formation with a telescope in order to block most of the starlight before it reaches the entrance pupil thereby allowing planetary light outside of the occulter's inner working angle to become visible. Designing a shape for the occulter spacecraft to enable suppression over a wavelength band of interest requires modeling through scalar diffraction theory. Typical designs feature occulters that are tens of meters across at a separation of tens of thousands of kilometers from the space telescope. </p><p> In this dissertation, we focus on occulter design and scaling to enable experimental optical verification of occulters in the laboratory. We provide experimental results that establish a 10^-5 suppression level in the pupil and 10^-10 contrast in the focal plane, which are both approximately two orders of magnitude below the ideal performance of the testbed. We use numerical simulation to study the sensitivity of the occulter design in the laboratory and determine that performance is feature-size limited. We provide the design of a longer and flight-like occulter experiment, and study its sensitivity to determine the expected performance.</p>