The organic-metal interface is ubiquitous in a wide variety of natural environments and industrial applications. As a result, the interfacial chemistry has been studied for many decades. Specifically, the surfactant-metal interfaces play an important role in the prevention of metallic corrosion where surface active corrosion inhibitors are often used as a prevention method. Development of a spectroscopic method based on vibrational sum frequency generation, specifically for metal interfaces, is carried out with the goal of elucidating the surface structure of these molecules. The contribution to the signalarising from the metal substrate often plays a crucial role in the quantitative analysis of spectra. By adopting a phase-resolved detection scheme, the polar orientation of the organic molecule adsorbed on metal surfaces is experimentally obtained. Furthermore,the development of a novel acquisition scheme is demonstrated where the incident angle is scanned while simultaneously measuring the magnitude and phase of the nonlinear response. This enables the separation of all contributions to the nonlinear susceptibility tensor governing the response. Such an approach is especially useful when the conventional nonlinear vibrational technique is inaccessible in beam polarizations where the infrared field is perpendicular to the plane of incidence, due to the infrared surface selection rule of metals. Finally, this approach is used to examine the structure of a surfactant on iron surfaces. / Graduate / 2022-09-08

Parametric down-conversion (PDC) is a nonlinear optical process widely used to generate pairs of photons. It occurs when an intense laser traverses an optical parametric amplifier (OPA). When the gain of the amplifier is increased, the number of downconverted photons increases exponentially: this is the high-gain regime of PDC. High-gain PDC is potentially a versatile tool for metrology. It is a source of highly-entangled states and bright squeezed states for applications in quantum information and interferometry. In addition, the high number of photons in high-gain PDC makes it possible to use diodes and cameras directly, instead of single-photon detectors and coincidence-counting apparatus. However, all the quantum-optical experimental methods need to be generalized or adapted for a high-photon flux. Most of the theoretical and experimental techniques used or developed in this thesis aim to address this transition from low to high-photon flux of PDC. I theoretically and experimentally provide strategies to harness the mode structure of PDC, bringing us steps closer to a usable source of bright squeezed vacuum for interferometry and quantum imaging. I present experimental progress in reducing the number of frequency modes of high-gain PDC, which is naturally broadband, and consequently highly multimode. Our theory for high-gain PDC generated in a nonlinear crystal provides a set of modes containing physically meaningful information, i.e. the pairwise quantum correlations between independant modes. In addition, I provide a thorough discussion on the limit of SU(1,1) interferometry in regards to internal loss and gain unbalancing. Finally, I tie the frequency spectrum of high-gain PDC to the properties of vacuum fluctuations, allowing to predict the number of photons from first principles, making it a powerful tool for spectroradiometry. Those developments are a springboard towards usable high-gain PDC for metrology.

Self-trapped beams of light propagate while maintaining their initial intensity profile within a self-induced channel of high refractive index. When multiple self-trapped beams or filaments travel within the same medium, a diverse host of interactions are observed, including attraction, repulsion, fusion, annihilation, and birth. This thesis describes studies of interactions between large and small filament populations and/or beam-induced structures (waveguides) within polymer media. The understanding developed in this fundamental work was applied to design polymer cuboids – the cuboids that count – with computing-inspired functionality. First, the spontaneous self-organisation of randomly-seeded waveguides within a photopolymer material formed the basis of 3 operations: (i) data transfer; (ii) volumetric encoding; and (iii) binary arithmetic. The same material was used for 3D data storage using highly-intersecting waveguide lattices. The pursuit of enhanced capacity prompted an exploration of light coupling in waveguides with small angular separation and significant field of view overlap. Using multiple angled light sources, we successfully demonstrated single-step data writing and multiplexed data reading in these structures. Finally, we examined long-range interactions between 2 to 4 collinear beams within a spiropyran-functionalised hydrogel. The mechanism of refractive index increase in this medium – a light-induced volume contraction and expulsion of water – allowed beams to inhibit their neighbours’ self-trapping, with a clear relationship between number of neighbours and degree of inhibition. These observations were used to form the basis for an optical hydrogel NAND gate. / Thesis / Doctor of Philosophy (PhD)

No description available.

Nonlinear optical processes have been used for many years to cause light to behave in unique ways. These can influence various aspects of the light beams, including the spatial intensity profile. More specifically, a naturally divergent beam can maintain its initial beam profile when propagating through a nonlinear medium due to the increased refractive index causing focusing. This process is called self-trapping and can be elicited for both coherent and incoherent light in a number of nonlinear media. Analogous to this, modulation instability (MI) is a nonlinear process that causes a broad beam of light of break up into a large population of self-trapped filaments. When these processes occur in photopolymers, light guiding structures are inscribed within the material and persist even after the light is removed. Our group has previously studied the behaviour and interactions of light undergoing self-trapping and MI in photopolymer systems. The studies presented in this thesis show novel interactions between multiple incoherent beams undergoing MI, utilization of these interactions, as well as the development of new polymeric systems capable of inducing MI. The filaments produced when orthogonal beams underwent simultaneous MI would align with themselves, forming highly ordered structures within the material. These interactions were used as the basis of an encoding and computing system based on the specific ordering of the resulting filaments. The mechanical properties of the resulting polymers were improved and tuned by developing a long-chain organosiloxane based system. The embedded waveguide structures are capable of guiding light when significantly deformed and restore to their initial parameters. A hydrogel system was also developed that was capable of producing self-trapping and MI with incoherent light. The samples were tested with biological systems and were also used to produce dynamic lens samples with enhanced angle of view. / Thesis / Doctor of Philosophy (PhD)

The synthesis and characterization of phosphorus containing poly(arylene ether)s were investigated to determine the effect of phosphorus upon the thermal stability, mechanical strength, and fire resistance of thermoplastics. Phosphorus containing activated aromatic dihalides and bisphenols were synthesized in high purity. These monomers were successfully polymerized via nucleophilic aromatic substitution to afford high molecular weight polymers. It was determined that by incorporating the phosphine oxide moiety into the polymer backbone certain properties of the resulting poly(arylene ether)s were substantially improved, such as an increase in T_g, thermal stability in air, modulus, and char yield, compared with control poly(arylene ether sulfone)s. The high char yields obtained for these polymers in air, along with observed intumescence indicates that these materials have improved fire resistance. Preliminary cone calorimetry measurements support this conclusion. In addition, the phosphine oxide group in the backbone was reduced to a phosphine and successfully converted to a phosphonium bromide ionomer. The resulting system was further chemically modified to ionically bond second-order nonlinear optical chromophores to the backbone of selected poly(arylene ether)s. Initial results on corona poling of cast film at low temperature produced stable second harmonic generation in these materials, indicating that they may have promise in nonlinear optical applications. / Ph. D.

This dissertation reports a sensitive single beam experimental technique for measuring nonlinear refraction and nonlinear absorption in a wide variety of materials. The experimental setup is described and a comprehensive theoretical analysis including cases where nonlinear refraction and nonlinear absorption are also presented.

Intensive demands have arisen to characterize nonlinear optical properties of materials for applications involving optical limiters, waveguide switches and bistable light switches. The technique of Pulse Delay Modulation is described which can monitor nonlinear changes in transmission with shot noise limited signal-to-noise ratios even in the presence of large background signals. The theoretical foundations of the experiment are presented followed by actual measurements of beam depletion due to second harmonic generation in a LiIO3 crystal and two-photon absorption in the semiconductor ZnSe. Sensitivity to polarization rotation arising from the Kerr Effect in carbon disulfide, saturable absorber relaxation in modelocking dyes and photorefractive effects in ZnSe are demonstrated. The sensitivity of Pulse Delay Modulation is combined with Fabry-Perot enhancement to allow the measurement of two-photon absorption in a 0.46pm thick interference filter spacer layer. Also included is a study of nonlinear optical limiting arising from dielectric breakdown in gases.

published_or_final_version / abstract / Electrical and Electronic Engineering / Master / Master of Philosophy

Fluorinated norbornene monomers exhibit the requisite properties for inclusion in 157 nm photoresists, but traditional addition and radical polymerizations with these monomers have failed. Norbornanediols provide an alternate route to these materials via condensation polymerization, and methods have been developed for the efficient synthesis of the exo-2-syn-7- and endo-2-exo-3-dihydroxynorbornanes. Synthesis of the fluorinated analogues is complicated by steric and electronic effects; however, a high-yielding synthesis of endo-2-exo-3-dihydroxynorbornane bearing a 5-endo-[2,2-bis(trifluoromethyl)hydroxyethyl] substituent as well as its corresponding polymer are reported. As an alternative to 157 nm and other optical lithographies, Step and Flash Imprint Lithography, or S-FIL®, was introduced in 1999 by The University of Texas at Austin. It has proven to be a cost effective, high resolution alternative to traditional optical lithography. Often in the S-FIL process, residual resist may become imbedded within the template features resulting in device defects due to the imprint and repeat nature of S-FIL. The high silicon and cross-linking content of the resist formulations are extremely difficult, if not impossible to remove from quartz imprint mold without template degradation. Our approach to this problem was the synthesis of a family of thermally reversible, cross-linkable monomers that will facilitate resist removal while maintaining template integrity. Our monomers utilize classic Diels-Alder chemistry to provide thermal reversibility, while pendant acrylate functionalities facilitate cross-linking. Herein we report the synthesis of several Diels-Alder compounds, incorporate them into resist formulations, and test their efficacy for resist removal. In an effort to develop unique patternable materials, our laboratory is currently engaged in the design and development of photonic crystals comprised of organic elements with highly stable electro-optic activity. Fabrication of these devices requires polymers that can be patterned at high resolution, have large second order nonlinear optical (NLO) coefficients, and that are thermally stable after poling. Our route to these materials involves the synthesis of a prepolymer that can be spin coated, poled, and then fixed by a photochemical cross-linking reaction. We now describe an efficient synthetic route to a new class of biscross-linkable monomers and the characteristics of their corresponding nonlinear optical polymers. / text