Quantum information science has shown that computers which exploit the quantum nature of particles, namely quantum computers, can outperform contemporary computers in some computational tasks. The fundamental building blocks of a quantum computer are quantum logical gates and quantum bits (qubits). Previous research has shown that the optical approach to quantum computing is promising. However, linear optical quantum computing (LOQC) schemes require a huge amount of resource, which makes large scale LOQC impractical, and hence there have been renewed interests in nonlinear optical quantum computing schemes, where less resource is required. The performance of these quantum gates depends on the properties of the nonlinear media. However, requirements on some of the properties for high performance quantum gates are not fully known. This thesis intends to bridge this gap of knowledge and examines the necessary conditions on several types optical nonlinearities that are common in two-qubit quantum gates schemes. These types of nonlinearities are, namely two-photon absorption, $\chi^{(2)}$ nonlinearity and $\chi^{(3)}$ cross-Kerr nonlinearity. The two-photon absorption based quantum Zeno gate is modeled in this thesis. It is shown that for practical absorbers, the photon loss significantly lowers the quantum fidelity of the Zeno gate. Nevertheless, this thesis proposes to use the Zeno gate for fusing optical cluster states. With the best theoretical estimate of single photon loss in the absorbers, the Zeno gate can outperform linear optical schemes. This thesis also proposes to embed the Zeno gate in the teleportation-type of two-qubit gate, namely GC-Zeno gate, such that the success rate of the gate can be traded off for higher gate fidelity. The effect of some mode matching error and detector inefficiency on the GC-Zeno gate are also considered here. It is shown that the photon loss requirement as well as the mode matching requirement are both stringent for having a fault tolerant GC-Zeno gate. This thesis models some of the properties of a $\chi^{(3)}$ optical medium and explores how they affect the fidelity of the cross-Kerr nonlinearity based quantum gate. This thesis shows that for a cross-Kerr medium with fast time response but negligible wave dispersion, the medium would induce spectral entanglement between the input photons and this significantly lowers the fidelity of the quantum gate. Nevertheless, when the dispersion has a stronger effect than the time response, and if phase noise is negligible, it is possible to achieve a quantum gate with high fidelity. However, the noise is actually significant, and this thesis suggests that spectral filtering can be applied to prohibit the occurrence of the noise. The requirements on employing optical $\chi^{(2)}$ nonlinearity for quantum computing are also examined. This study models the spectral effects of a $\chi^{(2)}$ medium on its efficiency. It is shown in this thesis that since the Hamiltonian of the medium does not commute at different times, the unitary operation should be modeled by a Dyson series, which leads to undesired spectral entanglement that lowers the efficiency of the medium. However, in the case of periodical poling, the unitary operation can be modeled by a Taylor series, where under some phase matching conditions, the medium can have a high efficiency. Furthermore, this thesis proposes a Bell measurement scheme and a quantum gate scheme based on $\chi^{(2)}$ nonlinearity that can always outperform linear optics even when the nonlinearity strength is weak. In the case of sufficiently strong nonlinearity, a quantum gate with high success rate can be achieved. In summary, this thesis models some of the properties of two-photon absorbers, $\chi^{(2)}$ nonlinearity and $\chi^{(3)}$ nonlinearity, and shows that it is possible to achieve the conditions required for high performance quantum gates, however these conditions are experimentally challenging to meet.

Neste trabalho usamos pulsos de femtossegundos na fabricação de estruturas poliméricas em escala microscópica, através da técnica de fotopolimerização via absorção de dois fótons. Graças ao confinamento espacial da polimerização, resultante do processo de absorção de dois fótons, este método permite a fabricação de microestruturas tridimensionais complexas, com alta resolução, visando diversas aplicações tecnológicas, de fotônica até biologia. Inicialmente, desenvolvemos a técnica de fotopolimerização via absorção de dois fótons, desde a implantação da montagem óptica até a confecção dos sistemas de movimentação e controle do posicionamento do feixe laser. Através da fabricação e caracterização de microestruturas, produzidas em resinas acrílicas, o sistema foi aperfeiçoado permitindo a produção de microestruturas da pordem de 30um com razoável resolução espacial. Uma vez que a maior parte as microestruturas reportadas na literatura são elementos passivos, ou seja, suas propriedades ópticas não podem ser controladas por meios externos, numa segunda etapa deste projeto produzimos microestruturas opticamente ativas. Neste caso, a microfabricação foi feita em resinas acrílicas dopadas Rodamina B, exibindo, portanto, fluorescência quando excitadas com luz de comprimento de onda em torno de 540nm. Finalmente, visando a produção eficiente de estruturas em escala milimétrica para aplicações biológicas, implementamos também um sistema de fotopolomerização via absorção de um fóton. / In this work we used femtosecond pulses to fabricate polymeric structures at microscopic scale, by using the two-photon photopolymerization technique. Due to the spatial confinement of the polymerization, provided by the two-photon absorption, this method allows for the fabrication of complex three-dimensional microstructures, with high resolution, aiming to several technological applications, from photonics to biology. Initially, we developed the two-photon polimerization technique, from the optical setup to the mechanical systems to control the movement and the positioning of the laser beam. Through the fabrication and characterization os microestrutures, produced in acrylic resin, the apparatus was improved, allowing the fabriation of 30-um microstructures with reasonable spatial resolution. Since most the report in the literature are passive elements that is, their optical properties cannot be altered by any external means, in a second stage of this project we fabricated optical active microstructures. In this case, the microfabrication was carried out in acrylic resins doped with Rodamine B, exhibiting, consenquently, fluorescence when excited with light at 540nm. Finally, in order to eficiently produce milimetric structures for biological applications, we also implemented a one-photon polimerization setup.

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.

Two-photon absorbing (2PA) materials has been widely studied for their highly localized excitation and nonlinear excitation efficiency. Application of 2PA materials includes fluorescence imaging, microfabrication, 3D data storage, photodynamic therapy, etc. Many materials have good 2PA photophysical properties, among which, the fluorenyl structure and its derivatives have attracted attention with their high 2PA cross-section and high fluorescence quantum yield. Herein, several compounds with 2PA properties are discussed. All of these compounds contain one or two fluorenyl core units as part of the conjugated system. The aim of this dissertation is to discuss the application of these compounds according to their photophysical properties. In chapters 2 to 4, compounds were investigated for cell imaging and tissue imaging. In chapter 5, compounds were evaluated for photodynamic therapy effects on cancer cells. Chapters 2 and 3 detail compounds with quinolizinium and pyran as core structures, respectively. Fluorene was introduced into structures as substituents. Quinolizinium structures exhibited a large increase in fluorescence when binding with Bovine Serum Albumin (BSA). Further experiments in cell imaging demonstrated a fluorescence turn-on effect in cell membranes, indicating the possibility for these novel compounds to be promising membrane probes. Pyran structures were conjugated with arginylglycylaspartic acid peptide (RGD) to recognize integrin and introduced in cells and an animal model with tumors. Both probes showed specific targeting of tumor vasculature. Imaging reached penetration as deep as 350 µm in solid tumors and exhibited good resolution. These results suggest the RGD-conjugated pyran structure should be a good candidate probe for live tissue imaging. Chapter 4 applied a fluorene core structure conjugated with RGD as well. Application of this fluorenyl probe compound is in wound healing animal models. Fluorescence was collected from vasculature and fibroblasts up to ≈ 1600 µm within wound tissue in lesions made on the skin of mice. The resolution of images is also high enough to recognize cell types by immunohistochemical staining. This technology can be applied for reliable quantification and illustration of key biological processes taking place during tissue regeneration in the skin. Chapter 5 describes three fluorenyl core structures with photoacid generation properties. One of the structures showed excellent photo-induced toxicity. Cancer cells underwent necrotic cell death due to pH decrease in lysosomes and endosomes, suggesting a new mechanism for photodynamic therapy.

The discovery of any new technology is usually accompanied by a need for new or improved materials which make that technology useful in practical applications. In the case of two-photon absorption (2PA) this has truly been the case. Since its first demonstration in 1961, there has been an ever increasing quest to understand the relationships between two-photon absorption and the structure of two-photon absorbing materials. This quest has been motivated by the many applications for 2PA which have been reported, including fluorescence bioimaging, 3D microfabrication, 3D optical data storage, upconverted lasing, and photodynamic therapy. The work presented in this dissertation represents another step in the effort to better understand the structure/property relationships of 2PA. In this work a new, squaraine-fluorenesquaraine molecule, proposed through a joint effort of quantum and synthetic chemists, was synthesized and its photophysical properties were measured. The measurements included linear and two-photon photophysical properties, as well as solvatochromic behavior. Quantum calculations were done to aid in understanding those photophysical and solvatochromic properties. A single squaraine dye was also synthesized and used as a model compound to assist in understanding this new structure. In Chapter 1 an introduction to 2PA and several of its applications is given. Chapter 2 gives a background of 2PA structure/property relationships that have been reported to date, based on work done with polymethine dyes. Chapter 3 gives a full account of the synthesis, characterization, and detailed quantum chemical analyses of this new squaraine-fluorenesquaraine molecule and the corresponding model compound squaraine dye. Chapter 4 gives some additional work and suggested future directions.

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Un tiers des urgences dentaires et un pourcentage élevé de maux de dents sont endodontie liés. Instruments rotatifs utilisés dans le traitement endodontique peuvent se briser à l'intérieur du canal radiculaire en raison de la fatigue des matériaux. Une fois cassé, l'extraction de la partie fracturée du canal est un travail difficile et ennuyeux de le patient et le dentiste. Par conséquent, l'alerte d'une fracture imminente lors de l'utilisation clinique ou développer de bonnes stratégies pour augmenter ses propriétés mécaniques sera d'une grande aide pour éviter les complications médicales / juridique. La recherche est étudié à partir de deux parties. La première partie a établi une plate-forme de test standard, simulant plusieurs paramètres de canal, propose une série de stratégies visant à améliorer la vie de la fatigue et des propriétés mécaniques de matériaux. Aussi, un système de surveillance utilisant de réseaux de Bragg (FBG) capteurs a été tentée. la raison de l'utilisation de la glycémie à jeun est sa petite taille qui est très prometteur dans l'intégration avec la pièce à main de l'équipement endodontique. dans le travail actuel, en ramassant et en analysant l'onde de contrainte par transformée de Fourier rapide (FFT), nous peut révéler la variation d'énergie et la fréquence phénomène déplaçant dans certaines fréquences caractéristiques. on espère que, avec ces informations, nous pouvons éviter / atténuer la survenue de fracture inattendue. Comme pour l'essai de fatigue, les données ont montré que la résistance à la fatigue peut être améliorée certain traitement thermique ou à mouvement alternatif méthode de rotation appliqué. tel phénomène peut être étroitement liée à la composition de la phase en ni-Ti en alliage et la contrainte de traction maximale est réduite lorsque le mouvement alternatif appliqué. études ont montré que plus la teneur de la phase martensite dans l'aiguille, l'plus de vie à la fatigue peut être atteint. Cependant, il peut être nécessaire de prendre des compromis avec l'efficacité de coupe de l'aiguille. pour cette question, nous pouvons combiner le traitement cryogénique et traitement thermique pour obtenir une meilleure résistance à la fatigue sans compromettre son efficacité de coupe. La deuxième partie est de fabriquer haute résolution, grande taille de la nouvelle Type aiguilles d'endodontie en utilisant la polymérisation à deux photons (TTP) technique. Le travail se fait à l'université de Joseph-Fourier LiPhy laboratoire, France. Contrairement à la fabrication traditionnelle du PPT, qui avait une limitation de sa taille de produits en raison du faible pouvoir lase, taux de redoublement et piézo entraîné stade, nous utilisons résine Ormocer, 130 kHz, 1W puissant laser de 532 nm à l'étape motorisé étage XY pour fabriquer une grande 800 échafaud um cellulaire bio-compatible et 1.2 cm aiguille de hauteur. aussi, pour améliorer la qualité du produit de TPP, l'approche de correction de la puissance du laser avait été tentée. Pendant TPP fabrication, la forme de focalisation laser changé lorsque la surface de la fabrication a été déplacé dans la direction z. Cela se traduit par le fait que nous avons besoin de plus afin d'assurer la taille de voxel est identique à z différent. pour corriger ce défaut, un procédé pour la correction de la puissance du laser et de la formule pour la puissance de correction sont proposées. la formule est dérivé du concept de maintien de conditions d'exposition identiques. / One third of dental emergencies and a high percentage of toothaches are endodontics related. Rotary instruments employed in endodontic treatment may break inside the root canal due to material fatigue. Once broken, extracting the fractured part from the canal is a difficult job and is annoying to both the patient and the dentist. Therefore, warning of an imminent fracture during clinical use or developing good strategies to increase its mechanical properties will be a great help to avoid medical/ legal complications. The research is studied from two parts. The first part established a standard testing platform, simulating several root canal parameters, proposing a series of strategies to improve the fatigue life and material's mechanical properties. Also, a monitoring system employing Fiber Bragg Grating (FBG) sensors has been attempted. The reason of using FBG is its small size which is very promising in integrating with the handpiece of the endodontic equipment. In the current work, by picking up and analyzing the stress wave through Fast Fourier Transform (FFT), we can reveal the energy variation and the frequency shifting phenomenon under some characteristic frequencies. It is hoped that with these information, we can avoid/alleviate the occurrence of unexpected fracture. As for the fatigue test, data showed that the fatigue life can be improved when certain heat treatment or reciprocating rotation method applied. Such phenomenon may be closely related to the phase composition in Ni-Ti Alloy and the maximum tension stress is decreased when reciprocating movement applied. Studies showed that the more content of martensite phase in the needle, the more fatigue life can be achieved. However, it may need to take compromise with needle's cutting efficiency. For this issue, we can combine cryogenic treatment and heat treatment to get better fatigue life without compromising with its cutting efficiency. The second part is to fabricate high resolution, large size of new type endodontic needles by employing two-photon polymerization (TTP) technique. The work is done in the university of Joseph-Fourier LiPhy lab, France. Unlike traditional TPP manufacturing, which had a limitation of its products size due to small lase power, repetition rate and piezo driven stage, we use Ormocer resin, 130 kHz, 1W powerful 532 nm laser with step motor driven X-Y stage to fabricate high bio-compatible 800 µm cell scaffold and 1.2 cm height needle. Also, to improve the product quality of TPP, the laser power correction approach had been attempted. During TPP fabrication, the laser focusing shape changed when the fabrication surface was moved up in z direction. This results in that we need more power to ensure the voxel size is the same at different z. To correct such defect, a method of the laser power correction and formula for the correcting power are proposed. The formula is derived from the concept of keeping exposure condition the same.

The purpose of this thesis is to investigate the nonlinear phenomena known as doubly-stimulated, non-degenerate two-photon emission (ND-2PE) in Gallium Arsenide (GaAs). 2PE refers to the simultaneous emission of two-photons as electrons move from the conduction band in a direct gap semiconductor to the valence band. Following the same path for describing one-photon emission (1PE) we describe 2PE as a product of the irradiance, and the negative of the loss which in this case is two-photon absorption, , the negative coming from the population inversion. We attempt to observe 2PE by using a frequency non-degenerate pump-probe experiment in which a third beam optically excites a 4 µm thick GaAs sample. We use nondegenerate beams in hopes of utilizing the 3-orders of magnitude enhancement seen in twophoton absorption (2PA) by going to extreme nondegeneracy (END) to enhance 2PE. GaAs is chosen due to the availability of the appropriate wavelengths, the maturity of the GaAs technology, its use in optoelectronic devices and its ability to be electrically pumped. During the experimental development we learn how to effectively etch and manipulate thin GaAs samples and model the transmission spectrum of these samples using thin film transmission matrices. We are able to match the measured transmission spectrum with the theoretical transmission spectrum. Here we etch the bulk GaAs left on the sample leaving only the 4 µm thickness of molecular beam epitaxial grown GaAs plus additional layers of aluminum gallium arsenide (AlGaAs). These samples were grown for us by Professor Gregory Salamo of the University of Arkansas. iv Using the pump-probe experiment on the 4 µm GaAs sample, we measure the change of the 2PA due to the presence of optically excited carriers. The goal is to reduce the 2PA signal to zero and then invert the 2PA signal indicating an increase in transmission indicative of 2PE when the population is inverted. Our results show that we achieve a 45% reduction in the 2PA signal in a 4 μm thick GaAs sample due to the excited carriers. Unfortunately, we currently cannot experimentally determine whether the reduction is strictly due to free-carrier absorption (FCA) of our pump or possibly due to a change in the two-photon absorption coefficient. We measure the transmission of various wavelengths around the bang gap of GaAs as a function of excitation wavelength and achieve a transmittance of ~80% which we attribute to possibly be one photon gain (1PG) at 880 nm. We also go to cryogenic temperatures to concentrate the carriers near the bottom of the conduction band and improve the theoretical gain coefficient for 2PE. Unfortunately, we do not observe a measurable change in 2PA with the addition of optically excited carriers. Along with FCA of our infrared pump we suspect that the difficulties in this first set of experiments are also a result or radiative recombination due to amplified spontaneous emission reducing our free carrier density along with the fact that 4 m is too thick for uniform excitation. We now have 1 m samples from Professor Gregory Salamo which we hope will give better and more definitive results

<p>Highly correlated quantum chemical methods have been appliedto study the photophysical properties of substituted benzenes.With the inclusion of spin-orbit coupling, the phosphorescencesof these molecules have been calculated usingMulti-CongurationalSelf- Consistent Field (MCSCF) quadraticresponse theory. The Herzberg-Teller approximation has beenadopted to evaluate the vibronic contributions tophosphorescence.</p><p>The performance of hybrid density functional theory (DFT) atthe B3LYP level is examined in comparison to the MP2, CCSD andCCSD(T) methods for the geometry and permanent dipole moment ofp-aminobenzoic acid. The time-dependent DFT/B3LYP method isapplied to calculate the two-photon absorption of a series ofZinc-porphyrin derivatives in combination with a two-statemodel. The transitions between excited singlet and tripletstates of Zinc and Platinum based organometallic compounds havebeen computed using DFT quadratic response theory. The resultsare used to simulate the non-linear propagation of laser pulsesthrough these materials utilizing a dynamical wave propagationmethod.</p>

<p>Two-photon excited fluorescence microscopy (TPM) has become a standard biological imaging tool due to its simplicity and versatility. The fundamental contrast mechanism is derived from fluorescence of intrinsic or extrinsic markers via simultaneous two-photon absorption which provides inherent optical sectioning capabilities. The NIR-II wavelength window (1000–1350 nm), a new biological imaging window, is promising for TPM because tissue components scatter and absorb less at longer wavelengths, resulting in deeper imaging depths and better contrasts, compared to the conventional NIR-I imaging window (700–1000 nm). However, the further enhancement of TPM has been hindered by a lack of good two-photon fluorescent imaging markers in the NIR-II. </p><p>In this dissertation, we design and characterize novel two-photon imaging markers, optimized for NIR-II excitation. More specifically, the work in this dissertation includes the investigation of two-photon excited fluorescence of various highly conjugated porphyrin arrays in the NIR-II excitation window and the utilization of nanoscale polymersomes that disperse these highly conjugated porphyrin arrays in their hydrophobic layer in aqueous environment. The NIR-emissive polymersomes, highly conjugated porphyrins-dispersed polymersomes, possess superb two-photon excited brightness. The synthetic nature of polymersomes enables us to formulate fully biodegradable, non-toxic and surface-functionalized polymersomes of varying diameters, making them a promising and fully customizable multimodal diagnostic nano-structured soft-material for deep tissue imaging at high resolutions. We demonstrated key proof-of-principle experiments using NIR-emissive polymersomes for in vivo two-photon excited fluorescence imaging in mice, allowing visualization of blood vessel structure and identification of localized tumor tissue. In addition to spectroscopic characterization of the two-photon imaging agents and their imaging capabilities/applications, the effect of the laser setup (e.g., repetition rate of the laser, peak intensity, system geometry) on two-photon excited fluorescence measurements is explored to accurately measure two-photon absorption (TPA) cross-sections. A simple pulse train shaping technique is demonstrated to separate pure nonlinear processes from linear background signals, which hinders accurate quantification of TPA cross-sections.</p> / Dissertation