Master of Science (M.S.), University of Dayton, 2015, Electro-Optics

Nonlinear absorption is a phenomenon in which the transmission of light through a sample is dependent upon the intensity of the incident light, caused by the process of two photon and carrier absorption. At low intensities the material will be transparent, but at high intensities the material will be opaque. Nonlinear refraction is a phenomenon by which the index of refraction of a material is dependent upon the incident intensity of the light. This leads to an effect known as self focusing, by which intense light creates a refractive gradient that focuses or defocuses the beam according to the transverse spatial distribution of the laser focus. These two properties are important in the development of optical switches. This work will measure these nonlinear properties for the material Cadmium Magnesium Telluride. Special attention is given to the relation of these properties to the bandgap of the compound, which is dependent upon the concentration of magnesium dopant. The data was collected using the Irradiance Scan technique in both the nanosecond and picosecond regimes, and the data was analysed using a four objective iterative approach involving both first order analytical approximations and a full numerical nonlinear propagation analysis.

Committee: Shekhar Guha Ph.D. (Committee Chair); Partha Banerjee Ph.D. (Committee Member); Jay Matthews Ph.D. (Committee Member) Subjects: Materials Science; Optics; Physics

Master of Science (M.S.), University of Dayton, 2014, Electro-Optics

The following research was born out of the observation of a counter-propagating beam (CPB) originating from the interaction of a pump beam and a Fresnel reflection inside an organic liquid held inside a fused silica cuvette. The strong influence on overlap with the Fresnel reflection is evidence for degenerate frequency two-beam coupling (TBC) via a transient phase grating. It is well known that TBC requires a phase shift between the fields and the induced grating which is supplied by the finite temporal response of the nonlinearity. TBC also requires a frequency shift between the interacting fields. For degenerate frequencies to couple, this shift must arise from self or cross phase modulation in the medium. In this work, we present a strong, degenerate frequency TBC in two organic systems using a single nanosecond beam where the probe is generated from the Fresnel reflection of the cuvette and the necessary phase and frequency shifts are the result of the thermo-optic effect and population redistribution. Its effect on the analysis of nonlinear transmission experiments and its relationship with Stimulated Rayleigh Bragg Scattering (SRBS) is also presented.

Committee: Joseph Haus Ph.D. (Committee Chair); Shekhar Guha Ph.D. (Committee Member); Daniel McLean Ph.D. (Committee Member) Subjects: Electromagnetism; Optics; Physics

Master of Science (M.S.), University of Dayton, 2011, Electro-Optics

Coherent tunable laser sources in the longwave infrared (LWIR) spectral region are in high demand for military applications. Most lasers cannot produce outputs far into the infrared region, and therefore a conversion process is needed to achieve desired wavelengths. Quasi-phase matching is a technique that spatially modulates the nonlinear properties of a given material, periodically reversing the induced nonlinear polarization to ensure positive energy flow from the pump source to the converted fields, subject to conservation of energy and momentum. Through the use of optical parametric oscillation (OPO), and nonlinear quasi-phase matched orientation-patterned gallium arsenide (OPGaAs), producing LWIR wavelengths is possible. The OPGaAs OPO was pumped with a Q-switched 2.054μm Tm,Ho:YLF laser. As a precursor to the LWIR OPGaAs OPO, different resonator geometries were explored with a midwave (MWIR) OPGaAs OPO utilizing both SRO and DRO mirror sets. While thresholds increased with cavity length, the slope efficiencies remained relatively similar with the respective mirror set. The LWIR OPGaAs OPO explored the performance using two separate cavity configurations, an SRO and an asymmetric cavity; and five different OPGaAs samples representing three different grating periods. The highest slope efficiency in the SRO LWIR cavity was found to be ~29%, with threshold values of ranging from ~45-90μJ. The slope efficiencies for the asymmetric cavity range from ~4-16% while experiencing higher thresholds of ~150-220μJ, lower overall output power, and increased cavity instability. At higher pump energies, rollover was observed in both cavity configurations. SNLO was used to model the OPO output in the hopes that it might provide some insight into this behavior. The theoretical performance plot fit the acquired data decently but failed to predict the behavior at the higher energies. Spectroscopic data were collected for both OPO signal and idler output, presenting good agreement (open full item for complete abstract)

Committee: Peter Powers PhD (Advisor); Rita Peterson PhD (Committee Member); Joseph Haus PhD (Committee Member) Subjects: Optics

Master of Science, The Ohio State University, 2024, Materials Science and Engineering

Cross-polarized wave (XPW) generation is a degenerate four-wave mixing process in which an intense linearly polarized incident wave is converted into a new linearly polarized wave in the orthogonal direction. This method can be used as a nonlinear filter to achieve temporal contrast enhancement and spectral broadening of ultra-short laser pulses. A nonlinear filter for contrast enhancement of ultrashort pulses and high conversion efficiency was seeded by Greater Average Yield (GrAY) Laser System delivering TW-level power at a 500 Hz repetition rate and 780 nm central wavelength to reach intensities of 1012 W/cm2. A cubic holographic-cut (h-cut) BaF2 crystal was used as a nonlinear medium to generate XPW. With a single crystal at 2.25 TW/cm2 input average intensity, a conversion efficiency of 11% was achieved. To overcome the early saturation of conversion efficiency with the single-crystal scheme, the double-crystal scheme was also investigated experimentally and theoretically. Regarding the efficiency of the XPW generation process, we have shown that working at lower input intensity levels is possible with the two-crystal approach. Achieving an optimal phase shift between the fundamental wave and XPW at the input of the second crystal, ~15% conversion efficiency at 0.52 TW/cm2 input average intensity was obtained with the double-crystal scheme. This led to a ~37% increase in conversion, which is in good agreement with the theory. A significant spectral broadening of 64 nm was also achieved with this arrangement. Moreover, transmitted XPW signal was cleaned from pre-pulses for both single and double-crystal schemes and contrast was improved at least by a factor of 40 and 50, respectively.

Committee: Enam Chowdhury (Advisor); Roberto Myers (Committee Member) Subjects: Materials Science; Physics

Master of Science (M.S.), University of Dayton, 2023, Electro-Optics

There are an increasing number of applications for high power lasers in medicine, industry and the military. Fiber lasers present an attractive alternative to traditional laser types; however, when operating at high power levels, fiber lasers are subject to detrimental nonlinear effects. Stimulated Brillouin scattering (SBS) is a nonlinear acousto-optic interaction where a stimulated acoustic wave scatters light, which limits the laser output. This thesis presents a theoretical and experimental framework for Brillouin scattering in continuous wave and pulsed beam regimes. Stimulated Brillouin scattering was observed in optical fibers in stationary and transient beam excitations and Brillouin frequencies are presented for different optical fibers with pulsed beam widths ranging from 15 ns to 500 ns.

Committee: Imad Agha (Advisor); Said Elhamri (Committee Co-Chair); David Zelmon (Committee Member); Andrew Sarangan (Committee Member) Subjects: Optics; Physics

PHD, Kent State University, 2023, College of Arts and Sciences / Department of Physics

Nonlinear optics has been a fascinating area of research for many years. Most recently nonlinear optical effects such as photovoltaic and photogalvanic effects became an active topic of research in the context of the recently discovered monochalcogenides. Group IV monochalcogenides monolayers (MMs) (GeS, GeSe, SnS and SnSe) are a special class of 2D materials which are of interest to researchers due to their tunability, large values of electronic mobility as well as high potential for optoelectronic applications. Those materials behave as 2D ferroelectrics, display bulk photovoltaic effect and serve as a platform to study relation between dimensionality and spontaneous polarization. Another class of advanced quantum materials – heavy-fermions – serve as a playground to study competing many-body ground states, such as superconductivity and magnetism. Most recently, some heavy-fermion systems, such as samarium hexaboride, have been predicted to exhibit a topologically nontrivial ground state, which lead to a flurry of experimental and theoretical activities. We studied the second harmonic generation (SHG) and injection current in MMs employing density functional theory (DFT) and validated the data through tight binding model. We showed that the JDOS, alone, cannot explain injection current in MMs but rather a combination of factors including, in-plane polarization, reduced dimensionality, anisotropy, and covalent bonding all of which are closely intertwined. I have also studied how the electron-electron interactions affect thermodynamic properties of Sm based and Ce-based heavy-fermion systems. Our work has been motivated by recent discovery of the Ce-based cage compounds CeNi2Cd20 and CePd2Cd20 which have vanishing RKKY interactions and do not exhibit a long-range order down to very low temperatures in the millikelvin range. We propose that d-wave superconductivity may develop in these compounds under an application of the hydrostatic pressure.

Committee: Maxim Dzero (Advisor); Benjamin Fregoso (Advisor); Artem Zvavitch (Committee Member); Gokarna Sharma (Committee Member); Almut Schroeder (Committee Member) Subjects: Physics

Doctor of Philosophy, The Ohio State University, 2023, Electrical and Computer Engineering

Lithium niobate (LN) has attracted significant interest over the past few decades as a potential platform for next generation nonlinear optical devices, high speed optical interconnects and modulators, and quantum light sources. Sub-micrometer thick lithium niobate on insulator (LNOI) is a promising integrated photonic platform that provides optical field confinement and high optical nonlinearity useful for state-of-the-art electro-optic modulators, wavelength converters, and acousto-optical devices. With fabrication foundry technologies enabling realization of low loss LNOI waveguides, devices fabricated using LNOI substrates and have been able to achieve record high harmonic generation efficiencies, and low insertion and propagation losses.Fabrication of LNOI on a silicon substrate through ion-slicing is advantageous for enabling velocity matching between microwave and optical copropagating fields in electro-optic modulators and for electronic-photonic integration but is challenging because of debonding and cracking due to thermal expansion coefficient mismatch between silicon and LN. Moreover, current techniques to pattern low loss waveguides with smooth sidewalls in LNOI rely on chemical mechanical polishing and electron beam lithography. Chemical mechanical polishing can result in film etching thickness variations, while electron beam lithography is not suited for high throughput production.Lastly, current schemes for fiber to chip edge coupling rely on the use of specialty optical fibers, such as lensed fibers, and there is a requirement for an efficient packaging solution that can utilize standard single mode cleaved optical fibers. Fabrication of thin film lithium niobate on insulator on a silicon handle wafer is achieved via ion-slicing, informed by structural modeling, and facilitated by accommodating for dissimilar wafer bows using a bonding apparatus. Structural finite element analysis of strain energy and stress, due to thermal expansion coefficient (open full item for complete abstract)

Committee: Ronald Reano (Advisor); Patrick Roblin (Committee Member); Robert Lee (Committee Member); Fernando Teixeira (Committee Member) Subjects: Electrical Engineering; Electromagnetics; Engineering; Nanotechnology; Optics

Doctor of Philosophy, The Ohio State University, 2022, Physics

As in all physical models, the response of a system to external perturbations is only approximately linear and with greater driving force, becomes nonlinear. The study of light interactions in solids is no different and with the development of laser technology, this can be explored with great detail. The use of femtosecond, and even few-cycle pulse lasers, allows for the study of very intense, localized interactions, which can range from frequency generation and spectral broadening of the incident pulse to photoionization of electrons and optical damage of the material itself. This work presents a trio of experiments that investigate the interaction of strong laser pulses with crystalline solids using femtosecond pulses. The first experiment characterizes the supercontinuum generation (SCG) in undoped, single-crystal yttrium aluminum garnet (YAG) optical fibers. Pump wavelengths near the zero-dispersion wavelength of YAG (1600 nm) are used to study SCG in both the normal and anomalous group-velocity dispersion (GVD) regimes. The output spectra of the fiber over many input pulse energies are collected for each pump wavelength and presented in 2D “energy scans.” Three different criteria are developed to help characterize the SCG in each energy scan. The second experiment looks at laser damage of gallium nitride (GaN) and gallium oxide (Ga2O3) using few-cycle pulses (FCPs) with a central wavelength near 760 nm. These experiments report on the damage thresholds as well as examine the crater morphology of single and multi-shot damage. Simulations using the Keldysh photoionization model and finite-difference time-domain method coupled to ionization and plasma effects are also employed to understand the carrier dynamics for single-shot exposure and possible mechanisms that differentiate FCP from longer femtosecond mechanisms. The final experiment returns to YAG in order to study damage under FCPs using a pump-probe technique known as time-resolved surface micro (open full item for complete abstract)

Committee: Enam Chowdhury (Advisor); Jay Gupta (Committee Member); Gregory Lafyatis (Committee Member); Douglass Schumacher (Committee Member) Subjects: Physics

Doctor of Philosophy, Case Western Reserve University, 2022, Physics

Polaritonic media have recently been shown to be an excellent material for nonlinear devices, and as test-beds for room temperature quantum phenomena and other fundamental physics. They are also exceptionally tunable and easy to construct. For nonlinear optics, the polaritonic resonance has been shown experimentally to dominate the expected output spectra and enhance the nonlinear processes. This requires a fundamental shift in predicting the nonlinear response of a system as more than a simple sum of its parts. This profound realization has culminated in many interesting scientific works, is evaluated in detail in this thesis, and plays a large role in the future of developing polaritonic devices for nonlinear optical devices. Beyond this, as light-matter entangled states, polaritons may also play a role in bringing quantum mechanical systems and processes to room temperature. This thesis explores some of the experimental evidence surrounding the nonlinear response of polaritons and their explication via quantum mechanics. We accomplish this primarily using the experimental techniques of z-scan and develop perturbation theory for a theoretical description of the nonlinear response. Additionally this thesis presents the application of machine learning (ML) to attribution of artistic works through their topography and the associated analysis of those ML algorithms at various length scales. The work contained in this thesis provides important stepping stones for future innovation and research in the areas of nonlinear optics of polaritons and the nexus of ML and art.

Committee: Kenneth Singer (Advisor) Subjects: Optics; Physics

Doctor of Philosophy (PhD), Ohio University, 2021, Chemistry and Biochemistry (Arts and Sciences)

Surfactants are extensively used as corrosion inhibitors to mitigate the internal corrosion of oil and gas pipelines. Surfactants are amphiphilic, consisting of both polar headgroup and nonpolar tail group. The arrangement of headgroup and tail group governs the adsorption as well as the inhibition process. In this dissertation, we explore the conformation of the short alkyl chain length and the nature of the headgroup of surfactants that affects on the ordering of interfacial water molecules. Quaternary ammonium compound (Quat) with five different chain lengths were synthesized via Quaternization of primary amine with Bromo alkane. Imidazolines with five different chain lengths were synthesized from fatty acid or aldehyde and amine. Aqueous solutions of Quat at different ionic strengths were studied by surface and interface selective sum frequency generation spectroscopy technique at the air-liquid interface. We found that Quat solutions containing 0%, 1%, and 10% NaCl salt showed no clear trend for the number of gauche defect as a function of ionic strength. In general, the longer chain surfactants were found to have more ordered interfacial water molecules compared to the shorter ones at the air-liquid interface. The SFG results were correlated with the surface tension measurements and pH values. As a continuation, the self-assembly of surfactant was also studied in-situ at the liquid-metal interface by SFG spectroscopy. A self-assembled monolayer at liquid-metal interface is vital for corrosion, catalysis, and electrochemical reactions. We probed the adsorption and self-assembly of Quats at the liquid-metal interface by SFG spectroscopy without applying any external potential. This provides direct evidence of the effect of alkyl chain length of surfactants in the conformational changes of an adsorbed monolayer on the liquid-metal interface. We found that longer chain surfactant forms highly ordered monolayer due to the strong tail-tail interaction. On the other (open full item for complete abstract)

Committee: Katherine Cimatu Dr. (Advisor); Jixin Chen Dr. (Committee Member); Micheal Held Dr. (Committee Member); John Staser Dr. (Committee Member) Subjects: Chemistry; Physical Chemistry; Physics

Doctor of Philosophy, The Ohio State University, 2020, Electrical and Computer Engineering

Single-crystal lithium niobate (LN) thin films have emerged as a promising platform for photonic integrated circuits with applications including quantum optics, spectroscopy, and high-speed communications. The LN films are well-suited for nonlinear optics owing to the high optical confinement compared to their bulk counterparts and their ferroelectric nature which enables quasi-phase matching by period poling. Poling of LN thin films presents new challenges due to large leakage currents and the relatively small domain size required for phase matching. Moreover, current poling techniques have not been able to reach submicrometer-scale poling periods suitable for first-order quasi-phase matched interactions with counter-propagating waves. In this dissertation, we fabricate lithium niobate thin films and demonstrate improved periodic poling techniques to enable efficient nonlinear photonic integrated circuits. Wafer-scale single-crystal LN thin films are produced by ion-slicing. The LN films are less than one micrometer thick and are bonded to a supporting oxidized LN wafer without the use any intermediate materials or adhesives. The films are chemically-mechanically polished to achieve a surface roughness less than 0.5 nm RMS. Large area void-free films are reliably produced with this process. In addition, fabrication processes to form silicon nitride strip-loaded waveguides and poling electrodes are developed based on electron beam lithography and plasma etching. A method of reducing the leakage current during electric field poling of x-cut magnesium oxide doped lithium niobate thin films is developed. The leakage current is reduced by introducing a silicon dioxide insulation layer under the co-planar electrodes. Uniform domains with a 7.5 μm period and 50% duty cycle are achieved. The poling characteristics are compared to bulk lithium niobate, with and without the silicon dioxide insulation layer. The domains are characterized on the surface by piezoresponse (open full item for complete abstract)

Committee: Ronald Reano Ph.D. (Advisor); Fernando Teixeira Ph.D. (Committee Member); Robert Lee Ph.D. (Committee Member) Subjects: Electrical Engineering; Electromagnetics; Optics

Doctor of Philosophy, The Ohio State University, 2017, Biophysics

Metalloproteins are essential to life, with roles in cellular signaling, metabolism, gas cycles, and gene regulation, among others. One group of metalloproteins is the ferritin-like superfamily, which contains a wide variety of members ranging from iron-trafficking proteins (ferritin) to enzymes that can perform 2-electron chemistry on hydrocarbons (bacterial multicomponent monooxygenases or BMMs). Ribonucleotide reductases (RNRs), one of the members of the ferritin-like superfamily, are enzymes that catalyze the only known de novo reduction of ribonucleotides to deoxyribonucleotides and are found is nearly every organism on earth. Recently, a novel protein was discovered in Mycobacterium tuberculosis called R2lox, because of its sequence similarity to the R2 subunit of RNR, whose function remains unknown. However, it does not possess any RNR activity and is more similar in active site structure and proposed function to the BMMs. This protein is very important from a basic science standpoint as well as a health science standpoint because of its unique metal-binding capabilities and because it is upregulated in the virulent H37rv strain of M. tuberculosis. To study the active site structure and oxygen activation reaction of this protein, a custom resonance Raman spectroscopic system was designed and built. This system is very versatile in that it can access many different wavelengths with a single laser, which is useful for resonance Raman, which relies on tuning the Raman excitation beam to an electronic absorption to enhance the scattering efficiency of Raman light. In addition to R2lox, this custom resonance Raman system has been used on numerous bioinorganic molecules to great effect. This work describes the design and construction of the custom resonance Raman system and its use in studying R2lox and other bioinorganic systems. Additionally, experiments were performed to lay the groundwork for studying electron transfer in R2lox via ruthenium modification.

Committee: Hannah Shafaat PhD (Advisor); James Cowan PhD (Committee Member); Terry Gustafson PhD (Committee Member); Marcos Sotomayor PhD (Committee Member) Subjects: Chemistry

Doctor of Philosophy (Ph.D.), University of Dayton, 2017, Electro-Optics

Optical parametric oscillators (OPOs) utilizing quasi-phase matched materials offer an appealing alternative to direct laser sources. Quasi-phase matched materials provide a useful alternative to traditional birefringent nonlinear optical materials and through material engineering, higher nonlinear coefficients can now be accessed. Orientation patterned gallium arsenide (OPGaAs) is an ideal material because of its broad IR transmission and large nonlinear coefficient. In contrast to ferroelectric materials, such as lithium niobate, where the pattern is fabricated through electric poling, zincblende materials, like OPGaAs, are grown epitaxially with the designed pattern. Generating longwave output from a much shorter pump wavelength, however, is relatively inefficiency due to the large quantum defect when compared to similar devices operating in the 3 – 5 µm regime. One method to increase pump to idler conversion efficiency is to recycle the undesired and higher energy signal photons into additional idler photons via a second nonlinear stage. An external amplifier stage can be utilized, where the signal and idler from the OPO are sent to a second nonlinear crystal in which the idler is amplified at the expense of the signal. Alternatively, the second crystal can be placed within the original OPO cavity where the signal from the first-stage acts as the pump for the second crystal and the resonant intensity of the signal is higher. Pumping the second crystal within the OPO should lead to higher conversion efficiency into the longwave idler. The grating period needed for the second crystal to use the signal from the first crystal to produce additional idler has the fortuitous advantage that it will not phase match to the original pump wavelength, avoiding unwanted nonlinear interactions. Therefore, a simple linear cavity can be utilized where the pump from the first-stage will simply propagate through the second crystal without undesired res (open full item for complete abstract)

Committee: Rita Peterson Ph. D. (Advisor); Joseph Haus Ph. D. (Committee Member); Partha Banerjee Ph. D. (Committee Chair); Monish Chatterjee Ph. D. (Committee Chair) Subjects: Optics

Doctor of Philosophy (Ph.D.), University of Dayton, 2017, Electro-Optics

The planned research is initially motivated by experiments on twisted fiber to examine the polarization of the output pulses. The initial polarization launched into the fiber evolves to a new final state that asymptotically moves to one of two opposite circular polarizations. The initial research was to program the vector wave equations of one and coupled solitons in a twisted fiber including the additional nonlinear terms stimulated Raman scattering and self-steepening. The high-twist fiber eliminates small linear birefringence at the expense of introducing circular birefringence manifested in the group velocities. The vector equations are naturally written in the circular polarization basis. To verify the numerical results, I made a sojourn to INAOE in Puebla, Mexico to run an experiment and compare the results. The numerical compare extremely well with the experimental results. For one soliton, the output polarization of the twisted fiber follows the input with high fluctuations. However, for the coupled soliton input, when the input polarization is close to linear, we observe a very abrupt polarization switch from nearly negative circular, -45° to nearly positive circular, 45° over a very narrow range of the input ellipticities. The literature is full of simulations of super-continuum generation using scalar wave equations, but we have not seen any report on the polarization of the output Supercontinuum light. Again, motivated by the experiments on polarization evolution in optical fibers we wanted to study the vector wave equations at higher incident powers to discover what the polarization state of the output waves are in an extreme nonlinear situation.

Committee: Joseph Haus (Advisor); Partha Banerjee (Committee Member); Andy Chong (Committee Member); Youssef Raffoul (Committee Member) Subjects: Engineering; Optics

Doctor of Philosophy (Ph.D.), University of Dayton, 2015, Electro-Optics

A thin film is a layer of a material or an assembly of multilayers of different materials ranging from nanometers to several micrometers in thickness. Optical coatings, optical filters, semiconductor lasers, quantum well structures, and nonlinear frequency convertors are some of the main applications of thin films. This dissertation is concerned with some aspects of optical propagation through, and at the interface of, some specific thin film structures, such as a double negative metamaterial and nonlinear photonic bandgap structures. A versatile imaging system that captures the near field radiation from subwavelength objects for high resolution imaging beyond the diffraction limit can be accomplished with new types of thin film materials not found in nature. One such material, termed a metamaterial with a double negative index, has been recently developed in our laboratory from a binary mixture of nanoparticles comprising silver and silicon carbide. A nanoscale structure comprising the sub-wavelength object, the single layer thin-film metamaterial superlens imaging setup to accurately characterize super resolution imaging for arbitrary polarized illumination of the object has now been fabricated as part of this dissertation and will be tested as part of future work. Secondly, electromagnetic wave reflection at a single interface is one of the most basic optical phenomena presented in nature. Snell's laws and the Fresnel equations determine the wave vectors and amplitudes for reflection and transmission. However, when a focused electromagnetic beam is incident at the interface between two layers, the reflected and transmitted beams suffer spatial shifts such as the Goos-Hanchen and Imbert-Fedorov shifts. In this dissertation, the Imbert-Fedorov shift is theoretically and experimentally investigated at the interface between air and a double negative index metamaterial. Finally, nonlinear effects such as optical second order and third order harmonic generati (open full item for complete abstract)

Committee: Partha Banerjee (Advisor) Subjects: Optics

Doctor of Philosophy, The Ohio State University, 2015, Physics

In the regime of strong-field physics the electric field of a laser begins to strongly rival the binding potential of an atomic or molecular species. During these interactions an ionized electron can be driven away and then back towards its parent ion by the strong laser field and undergo rescattering before being detected. The amount of energy an electron can acquire during propagation is proportional to the laser intensity and the square of the wavelength. Recent improvements in laser technology have allowed us to push strong-field studies from visible/near-infrared wavelengths to the mid-infrared regime and thereby greatly increase the electron's maximum recollision energy. These high energy scattering events imprint target dependent structural information on the electron angular distribution from which we can extract atomic and molecular specific properties. Further, Keldysh invariance suggests that we can control the dominant ionization mechanism (multiphoton absorption versus tunneling through the field modified potential) by choosing an appropriate laser wavelength, laser intensity and target atom. Exploratory investigations in strong-field physics have produced many fascinating results which have led to production of attosecond duration laser pulses and atomic/molecular imaging techniques. As technological improvements continue we are able to gain further insights into these interesting physical phenomena. In this work we examine photoelectron spectra and ion yields in order to gain a deeper understanding of the fundamental processes that underlie atomic and molecular strong field interactions. Alkali metal atoms at mid-infrared wavelengths possess similar Keldysh parameter values as noble gas atoms at near-infrared wavelengths, which have received much more investigative attention. Therefore, by examining alkali metal atoms at longer wavelengths we hope to expand on our understanding of the global, Keldysh invariant, and atom specific ionization features (open full item for complete abstract)

Committee: Louis DiMauro (Advisor); Frank De Lucia (Committee Member); Jay Gupta (Committee Member); Ralf Bundschuh (Committee Member) Subjects: Optics; Physics

Doctor of Philosophy, The Ohio State University, 2005, Physics

The propagation of an intense laser through transparent materials can only be understood by considering a wide range of nonlinear effects and their simultaneous interaction. Electron plasma formation plays a crucial role and is the focus of this work. The mechanisms of the nonlinear ionization are not well understood. There are two proposed interactions that contribute to electron plasma formation: photoionization and avalanche ionization, but the individual contribution of each of these ionization processes is controversial. Keldysh theory has been proposed as a description of photoionization. Two models for avalanche ionization are used in the literature, but with different intensity dependence. We address and resolve these issues. In this thesis we present a spectrally resolved pump-probe experiment that directly measures the nonlinear ionization rates and plasma evolution in solid state media. Both pump and probe are derived from an 800 nm, 120 fs laser. The maximum ionization rates were obtained in sapphire (~1.9×10 fs ·cm ), while in water (~7.2×10 fs ·cm ), fused silica (~8.6×10 fs ·cm ) and methanol (~6.6×10 fs ·cm ) the ionization rates were slightly different. Our measured ionization rates are consistently larger that the theoretical rate given by Keldysh theory, suggesting that this theory does not correctly describe the photoionization process. We also present measurements that separate the two excitation processes and identify the role played by each in the ionization of media. The idea underneath these experiments is a very simple one: since the two ionization processes have different intensity dependence, the absorption of light in the medium should differ similarly. Therefore it should be possible to distinguish the two mechanisms by looking at the energy dependence of the absorption. From our result we find that avalanche and multiphoton ionization have varying relative contributions, depending on the band gap. For example, in sapphire (band gap ~ 9 (open full item for complete abstract)

Committee: Douglass Schumacher (Advisor) Subjects:

Doctor of Philosophy, The Ohio State University, 2004, Physics

When a sufficiently energetic short laser pulse propagates through a medium it can generate an explosive increase in bandwidth leading to the creation of white light; this is known as supercontinuum generation (SCG). Although it is frequently referred to as a single process, SCG is actually the result of many different parallel and competing processes. In this work we investigate the contribution of the individual physical processes underlying the SCG effect, focusing specifically on Raman processes and plasma formation in sapphire. For our experiments we use an amplified Ti:sapphire laser system producing nearly transform limited 60 fs pulses at 800 nm. Typical pulse energies for the experiments are 1 – 3 microJ/pulse. Using a new experimental technique, the spectrally resolved interferometric double pump, we study the contribution of non-instantaneous Raman effects. We see two distinct Raman contributions in sapphire which are much stronger than indicated in previous work. One Raman process has a period of approximately 185 fs and is related to an available optical phonon; the second Raman process has a period of 20 fs and is related to defect states caused by an oxygen vacancy in the sapphire crystal. Data from the same experiment show that the SCG light is not phase stable at low excitation energies, but that the phase stability is restored and saturates with increasing laser intensity. In a separate experiment we investigate the dynamics of plasma formation using a pump-probe technique. We observe that in sapphire both the formation and the decay of the plasma occur over time scales much longer than predicted by current theory. The plasma rise time is ~225 fs, while the decay time is ~150 ps; we also observe that these values do not depend on input pulse energy. In addition to these experiments, we perform a numerical integration of the extended (3+1) dimensional nonlinear Schrodinger equation, which models the propagation of a short laser pulse through a nonli (open full item for complete abstract)

Committee: Douglass Schumacher (Advisor) Subjects: Physics, Optics

BA, Oberlin College, 2004, Physics and Astronomy

The thesis documents the work done over the year to initiate an undergraduate Advanced Laboratory experiment which tests Bell's inequality. It provides reference theory for the experiment, including explanations of Bell inequalities, basics of nonlinear optics, type-I downconversion and entanglement, and polarization states of the entangled photons. A main result is the equipment and design proposal for the experiment, which will cost a total $19600, led in price by the $9000 of a four photodetector array and followed by the $5000 of a 405nm pump laser. Entangled photons are produced by pumping BBO in a two-crystal geometry. Although most of the light is transmitted, some undergoes type-I parametric downconversion. Degenerate pairs are in a tunable entangled state and can be used to show non-classical behavior. Specifically, a violation of the CHSH Bell inequality can be observed. Usable coincidence rates of several thousand per second are expected. Experimental and data analysis methods are described as the basis of future laboratory documentation. Explanations of equipment alignment and adjustment and data collection are included, as well as derivations of relevant analyses of the experimental data. Lastly the coincidence circuit built for the experiment is reviewed. The circuit costs less than $40 to construct and demonstrates a coincidence window of between 18ns and 36ns.

Committee: Stephen Fitgerald PhD (Advisor) Subjects: Experiments; Optics; Physics; Science Education

Master of Science (M.S.), University of Dayton, 2010, Electro-Optics

In this work, a novel electro-optic beam switch (EOBS) is designed, fabricated and demonstrated. The EOBS presented in this work is designed for a Nd:YAG laser operating at λ = 1064 nm and is demonstrated to achieve >750 μm of beam translation at switching rates of up to 3 Hz. The EOBS consists of a series of electronically controlled prisms fabricated by ferroelectric domain inversion in an electro-optic crystal wafer. The prisms are arranged such that positive angular deflections are counterbalanced by subsequent negative angular deflections. The result is discrete beam translation with no angular deflection. In this work, an algorithm for designing optimal beam translation geometries is developed. Five of the resulting geometric designs are then fabricated in 5 mol% magnesium oxide doped congruent lithium niobate (5%MgO:CLN). The performance of one particular geometry is modeled in detail and analyzed experimentally. The EOBS is used to demonstrate wavelength tuning of a near-infrared laser system using a selectable optical parametric generation (OPG) grating.

Committee: Peter E. Powers (Committee Chair); Andrew Sarangan (Committee Member); Kenneth L. Schepler (Committee Member) Subjects: Optics