Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2007. / Source: Dissertation Abstracts International, Volume: 68-07, Section: B, page: 4567. Adviser: Paul G. Kwiat. Includes bibliographical references (leaves 72-74) Available on microfilm from Pro Quest Information and Learning.

Thesis (Ph.D.)--Lehigh University, 2008. / Adviser: Volkmar Dierolf.

Thesis (Ph.D.)--Indiana University, Dept. of Physics, 2008. / Title from PDF t.p. (viewed on Jul 29, 2009). Source: Dissertation Abstracts International, Volume: 69-12, Section: B, page: 7588. Adviser: Shyh-Yuan Lee.

Thesis (Ph.D.)--Lehigh University, 2008.

Thesis (Ph.D.)--Indiana University, Dept. of Physics, 2008. / Title from PDF t.p. (viewed on Oct. 7, 2009). Source: Dissertation Abstracts International, Volume: 70-02, Section: B, page: 1099.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2006. / Source: Dissertation Abstracts International, Volume: 67-07, Section: B, page: 3872. Adviser: Paul G. Kwiat. Includes bibliographical references (leaves 109-115) Available on microfilm from Pro Quest Information and Learning.

The multi-configuration time-dependent Hartree-Fock (MCDTHF) method is a promising new method that can solve the time-dependent Schrodinger equation (TDSE) for a correlated multielectron system. We have written a computer code to solve the MCTDHF equations of motion. This code is highly optimized for speed and makes efficient use of memory. As a first test of the code, we will investigate the ionization dynamics of N2 in a strong laser-electric field using two active electrons. By examining the final momenta, parallel to the field polarization direction, of the two ionized electrons we are able to determine: (i) which laser dressed excited state the second electron was in at the time of ionization and (ii) the birth times of the electrons in the field. The results of these calculations provide a means for characterizing the attosecond dynamics of atoms and molecules without using attosecond pulses.

In a distributed Brillouin sensor system, it is crucial to keep the pulse energy uniform for constant signal to noise ratio. This means that the variable DC leakage (pulse base) through the electro-optic modulator must be locked. In this thesis I examine two different methods of locking the pulse base level and look at the advantages and disadvantages of each locking method. It is found that the two locking methods, one based on a lock-in amplifier and the other using proportional-integral-derivative control, both have applications in which they excel at locking the pulse base. Also, a technique to simultaneously lock the pulse base, top, and width is developed and tested. In the field of structural health monitoring, it is often advantageous to monitor the dynamic behaviour of a structure in real-time. The traditional distributed Brillouin sensor does not allow for this dynamic measurement due to the need to sweep the frequency difference between the two lasers and subsequent averaging of waveforms. For the first time to our knowledge, a real-time vibration sensor based on polarization-state perturbations in stimulated Brillouin scattering instead of resonant frequency mismatching monitoring of the Brillouin spectrum has been proposed. The long measurement time of traditional distributed Brillouin sensors is avoided by eliminating the frequency sweep of the pump and Stokes lasers and instead locking them at a single beat frequency corresponding to the static strain of the structure in which the fiber is embedded. This unique sensor allows measurement of vibration frequencies along a sensing fiber as shown in laboratory experiments and also the detection of impact waves from passing vehicles in field tests in which the sensor was embedded in the concrete pavement of a highway. A 20 ns pulse width with potential spatial resolution of 2 m was used over a sensing length of 300 m. Also, studies of the Brillouin linewidth under cw pump and Stokes waves are done in order to confirm the validity of a new definition of the threshold power in Brillouin fiber amplifiers which involve both input pump and input Stokes waves - all previous threshold definitions took into account only the input pump power. Finally, some interesting lineshape characteristics such as spectral hole burning and side-lobes on the Brillouin spectrum are observed for high power 2 ns Stokes pulses and their origins explained qualitatively. The evolution of these features with increasing pump power is investigated. The effect of laser linewidth and fiber length on these features is also considered.

This thesis explores the production, characterization, and water oxidation efficiency of wide bandgap semiconductors made through femtosecond-laser irradiation of various materials. Our investigation focuses on three main aspects: 1) producing titanium dioxide (TiO2) from titanium metal, 2) using our laser-made materials in a photoelectrochemical cell for water oxidation, and 3) utilizing the femtosecond laser to create a variety of other mixed metal oxides for further water oxidation studies and biological applications. We first discuss producing TiO2 and titanium nitride. We report that there is chemical selectivity at play in the femtosecond laser doping process so not all dopants in the surrounding atmosphere will necessarily be incorporated. We then show that the material made from laser-irradiation of titanium metal, when annealed, has a three-fold enhancement in overall water oxidation when irradiated with UV light. We attribute this enhancement through various material characterization methods to the creation of a more pure form of rutile TiO2 with less defects. We then present a variety of studies done with doping both TiO2 and other oxides with broadband photoelectrochemistry and offer that the dopant incorporation hurts the overall water oxidation rate. Lastly, we use the laser-treated titanium to test cell adhesion and viability. Our results demonstrate an ability to femtosecond-laser process semiconductors to produce materials that no one has made previously and study their properties using collaborations across chemistry and biology, yielding true interdisciplinary research.

Gallium nitride (GaN) microcavities with embedded optical emitters have long been sought after as visible light sources as well as platforms for cavity quantum electrodynamics (cavity QED) experiments. Specifically, materials containing indium gallium nitride (InGaN) quantum dots (QDs) offer an outstanding platform to study light matter interactions and realize practical devices, such as on-chip light emitting diodes and nanolasers. Inherent advantages of nitride-based microcavities include low surface recombination velocities, enhanced room-temperature performance (due to their high exciton binding energy, as high as 67 meV for InGaN QDs), and emission wavelengths in the blue region of the visible spectrum. In spite of these advantages, several challenges must be overcome in order to capitalize on the potential of this material system. Such diffculties include the processing of GaN into high-quality devices due to the chemical inertness of the material, low material quality as a result of strain-induced defects, reduced carrier recombination effciencies due to internal fields, and a lack of characterization of the InGaN QDs themselves due to the diffculty of their growth and therefore lack of development relative to other semiconductor QDs. In this thesis we seek to understand and address such issues by investigating the interaction of light coupled to InGaN QDs via a GaN microcavity resonator. Such coupling led us to the demonstration of the first InGaN QD microcavity laser, whose performance offers insights into the properties and current limitations of the nitride materials and their emitters. This work is organized into three main sections. Part I outlines the key advantages and challenges regarding indium gallium nitride (InGaN) emitters embedded within gallium nitride (GaN) optical microcavities. Previous work is also discussed which establishes context for the work presented here. Part II includes the fundamentals related to laser operation, including the derivation and analysis of the laser rate equations. A thorough examination of the rate equations serves as a natural motivation for QDs and high-quality factor low-modal volume resonators as an optimal laser gain medium and cavity, respectively. The combination of the two theoretically yields the most efficient semiconductor laser device possible. Part III describes in detail the design, growth, fabrication and characterization of the first InGaN QD microcavity laser. Additional experiments are also conducted in order to conclusively prove that the InGaN QDs serve as the gain medium and facilitate laser oscillation within the microdisk cavities. Part III continues with work related towards the development of the next generation of nitride light emitting devices. This includes the realization of photonic crystal cavity (PCC) fragmented quantum well (FQW) lasers that exhibit record low lasing thresholds of 9.1 uJ/cm2, comparable to the best devices in other III-V material systems. Part III also discusses cavity QED experiments on InGaN QDs embedded within GaN PCCs in order to quantify the degree of light-matter interaction. The lack of experimental evidence for weak or strong coupling, in the form of the Purcell Effect or cavity-mode anti-crossing respectively, naturally motivates the question of what mechanism is limiting the device performance. Part III concludes with cathodoluminesence and tapered fiber measurements in order to identify the limiting factor towards achieving strong coupling between InGaN QDs and GaN microcavities.