The nonlinear refractive index (n2) of room temperature liquid CS2 in the wavelength range of 9 to 11 micrometers is measured. A line tunable hybrid C02 TEA laser and amplifier system is used for the experiments. In these measurements the well known photoacoustic method is utilized to observe the onset of whole beam self-focusing. The photoacoustic signal in a CS2 cell, much longer than the confocal parameter, is monitored. The departure of the acoustic signal from linear growth marks the critical power for the onset of nonlinearity. It is experimentally verified that the phenomenon is power dependent as expected from self-focusing theory. The value of n2 is then calculated from the theoretical model of self focusing. Measurements of the on-axis irradiance transmitted through the nonlinear material as well as the measurements of beam distortion are used to verify the validity of the photoacoustic method. In all the measurements the on-axis intensity was smaller than the calculated threshold intensity for stimulated Brillouin scattering. The back reflection was monitored to make sure that stimulated Brillouin scattering was not playing a role in the phenomenon.

Performance and reliability of solid state laser diodes in the IR region exceeds those in the visible and UV part of the light spectrum. Single frequency visible and UV laser diodes with higher than 500 mW power are not available commercially. However we successfully stabilized a multi-longitudinal mode IR laser to 860 mW single frequency. This means high efficiency harmonic generation using this laser can produce visible and UV laser light not available otherwise. In this study we examined three major leading nonlinear crystals: PPMgO:SLN, PPKTP and PPMgO:SLT to generate blue light by second harmonic generation. We achieved record high net conversion efficiencies 81.3% using PPMgO:SLT (~500 mW out), and 81.1% using PPKTP (~700 mW out). In both these cases an external resonance buildup cavity was used. We also studied a less complicated single pass waveguide configuration (guided waist size of ~ 5 um compared to ~60 um) to generate blue. With PPMgO:SLN we obtained net 40.4% and using PPKT net 6.8% (110mW and 10.1 mW respectively).

The third-order nonlinear optical (NLO) properties of indium tin oxide (ITO) thin films, Fe3+, Mn3+, Co2+ 5,10,15,20-tetrakis-4hydroxytetraphenyl)porphyrin (TPP) films, and a series of ethynyl-linked azobenzene oligomers were investigated using degenerate four wave mixing (DFWM) with 100 fs laser pulses. To measure the NLO of ITO thin films, A DFWM method for measuring thin films on thick substrates was refined for the characterization of films less than 100 nm thick and applied to ITO films ~25 nm thick. It was found that the third-order nonlinear susceptibility of ITO, χ(3)ITO, is purely electronic at 900 - 1300 nm (11000 - 7700 cm-1) and has a value of (2.16 ± 0.18) x 10-l8 m2 V-2. The χ(3)IT0 value reaches (3.36 ± 0.28) x 10-l8 m2 V(sup>-2 at 1500 nm (6700 cm-1) due to two-photon absorption by free carriers (electrons). Ultrafast electron relaxation was also observed. The ~100 fs lifetime of this process could reflect electron scattering in the conduction band. This DFWM method was also used to investigate the two-photon properties of ~500 nm thick electropolymerized films of Fe3+, Mn3+, and Co2+ TPP in the near-IR spectral region. Metalloporphyrins with strong charge transfer (CT) transitions inthe linear absorption spectra also show enhanced two-photon absorption. (Metalloporphyrin two-photon absorption cross section, δ, increases >10 times over that for the metal free porphyrin.) This effect was attributed to a two-photon induced charge transfer between the metal ion's d orbitals and the π-system of the porphyrin. Correlationof one- and two-photon absorption properties of transition metal porphyrins suggests a new and simple approach to improve organic materials for photonic applications. Finally, a series of oligomers consisting of ethynyl-linked azobenzene units was prepared using Pd-catalyzed cross coupling. The linear and nonlinear optical properties of the oligomers were investigated. The molecular second hyperpolarizability, γ, followed the power law γσ n2.12±0.05 (n is number of repeat units) for unusually large molecular lengths. The exceptional exciton delocalization length exceeds 360 conjugated bonds (>49 nm) and is attributed to the rigidity of the conjugated backbone.

Les nanostructures métalliques ont la capacité de supporter des résonances de plasmons de surface localisés se caractérisant par une oscillation collective des électrons libres du métal. Ce phénomène, connu pour générer localement un champ électrique intense, peut notamment être exploité afin d'exalter les processus d'optique non-linéaire à l'échelle nanométrique. Au cours de cette thèse, nous nous sommes intéressés au processus de génération de second harmonique (SHG) de nanostructures en aluminium et en or. Tout d'abord, nous avons étudié l'origine du processus non-linéaire et mis en évidence le rôle important joué, dans l'or, par la contribution non-locale, issue des gradients de champ dans le volume de la nanostructure. Ensuite, nous avons montré, en associant un phénomène de double résonance et un accord des modes plasmoniques à l'excitation et à l'émission, qu'il est possible d'exalter fortement la réponse harmonique d'une nanoantenne compacte en aluminium. Dans l'optique d'obtenir une intensité non-linéaire encore plus importante, une stratégie est de coupler ces nanostructures à un nanocristal non-linéaire afin de bénéficier à la fois de la forte exaltation du champ générée par le métal et de la non-linéarité du cristal. Afin d'optimiser l'intensité harmonique générée par ces structures hybrides, disposer de nanocristaux possédant une forte non-linéarité intrinsèque est nécessaire. C'est pourquoi, au cours de cette thèse, nous avons mesuré la réponse harmonique de nanocristaux d'iodates de lantane isolés, afin d'estimer leur potentiel pour intégrer ce type de structure. De plus, un microscope optique en champ proche a été mis en place sur le dispositif expérimental permettant la manipulation de nanocristaux à proximité de structures métalliques. Cette thèse, en apportant de nouveaux éléments pour comprendre et optimiser le processus de SHG dans les nanostructures plasmoniques, offre de nouvelles perspectives pour confectionner des composants optiques efficaces pour la conversion de fréquence à l'échelle nanométrique. / Plasmonic nanostructures have the ability to support localised surface plasmon resonances characterized by a collective oscillation of the free electrons in metal. This phenomenon, know to generate an intense local field, can be used to enhance nonlinear optical processes at the nanoscale level. In this thesis, we have investigated the second harmonic generation (SHG) process in aluminum and gold nanostructures. First, we have studied the origin of this nonlinear process and highlighted the major role played, in gold, by the bulk nonlocal contribution, originating from the field gradients inside the nanostructure volume. Then, we pointed out, by achieving a double resonance regime associated with a plasmonic mode matching at the excitation and emission, the possibility to enhance significantly the harmonic response of compact aluminum nanoantennas. In order to increase even more the nonlinear intensity, an idea is to couple these nanostructures to a nonlinear nanocrystal to benficiate both from the field enhancement provided by the metallic nanoantenna and from the nonlinearity of the nanocrystal. To optimise the harmonic intensity generated by these hybrid structures, have nanocrystals with a strong intrinsic nonlinearity is required. To this end, we have measured the harmonic response of single latanide iodate nanocrystals, in order to evaluate their ability to integrate this type of structure. Moreover, we have implemented a near-field optical microscope used to manipulate nancorystals in the vincinity of metallic nanostructures. This thesis, by bringing new elements to understand and optimise the SHG process in plasmonic nanostructures, provides new perspectives to elaborate efficient optical components to frequency conversion at the nanoscale.

We investigate two medium-facilitated interactions between properties of light upon propagation through optical fiber. The first is interaction between the spin and intrinsic orbital angular momentum in a linear optical medium. This interaction gives rise to fine structure in the longitudinal momenta of fiber modes and manifests in rotational beating effects. We probe those beating effects experimentally in cutback experiments, where small segments are cut from the output of a fiber to probe the evolution of both output polarization and spatial orientation, and find agreement between theoretical predictions and measured behavior. The second is nonlinear optical interaction due to cross- and self-phase modulation between the complex-valued temporal amplitude profile of pump pulses and the amplitude profiles of generated signal and idler pulses in optical fiber photon-pair sources utilizing the four-wave mixing process named modulation instability. We develop a model including the effects of these nonlinear phase modulations (NPM) describing the time-domain wave function of the output biphoton in the low-gain regime. Assuming Gaussian temporal amplitude profiles for the pump pulse, we numerically simulate the structure of the biphoton wave function, in symmetric and asymmetric group velocity matching configurations. Comparing the overlap of the joint temporal amplitudes with and without NPM indicates how good of an approximation neglecting NPM is, and we investigate the effects of NPM on the Schmidt modes. We find that effects of NPM are small on temporally separable sources utilizing symmetric group velocity matching, but appreciably change the state of temporally entangled sources with the same group velocity matching scheme. For sources designed to produce entangled biphotons, our simulations suggest that NPM increases the Schmidt number, which may increase entanglement resource availability with utilization of a phase-sensitive detection scheme. We find that NPM effects on temporally separable sources designed with asymmetric group velocity matching produce non-negligible changes in the state structure. The purity is unaffected at perfect asymmetric group velocity matching, but if the pump is detuned from the correct wavelength, the purity degrades. The largest changes to the state due to NPM occur in long fibers with long pulse durations and low repetition rates.

Neste trabalho utilizamos a técnica de mistura de duas ondas quase degeneradas na investigação das propriedades ópticas não lineares, associadas à mudança de índice de refração com a intensidade da luz, em materiais dopados com cromo: Al2O3:Cr3+ (rubi), BeAl2O4:Cr3+ (alexandrita) e GdAlO3:Cr3+ (aluminato de gadolínio dopado com cromo). A não linearidade Kerr para o GdAlO3: Cr3+ é bastante significativa, de modo que neste material o parâmetro de ganho do feixe de prova apresenta um comportamento muito peculiar e que não encontra explicação nos tratamentos teóricos usuais do processo de mistura de duas ondas. Em particular, o ganho do feixe de prova neste material atinge percentuais superiores a 200%. Desta forma, desenvolvemos um tratamento teórico que descreve a mistura de duas ondas quase degeneradas em meios onde o índice de refração depende da intensidade (n= n0+n2I). Esta abordagem teórica leva em consideração os efeitos de saturação da grade de população produzida pela intersecção dos feixes de luz no meio Kerr (não harmonicidades da grade) e o processo de mistura de duas ondas é considerado como um caso particular do fenômeno da auto-difração difração de ordem zero. Os resultados teóricos foram comparados com os resultados experimentais e várias previsões teóricas como, a dependência do parâmetro de ganho do feixe de prova com a intensidade de saturação do meio, a dependência da diferença de freqüência entre os dois feixes incidentes onde o ganho é máximo com a intensidade do feixe de bombeamento, foram confirmadas experimentalmente / In this work nearly degenerate two-wave mixing technique is used in order to investigate nonlinear optical properties, associated to the refractive índex change by incident light, in a few doped crystals: Al2O3:Cr3+ (ruby), BeAl2O4:Cr3+ (alexandrite) e GdAlO3:Cr3+ (gadolinium aluminate chromium doped). The Kerr nonlinearity in GdAlO3:Cr3+ is very high, so that the probe gain parameter has peculiar behavior in this material and this cannot be explained by using the current approach found in the literature. In particular, the probe gain parameter in this material reaches percentuals above 200%. In this way, we develop a theoretical approach which describes nearly degenerate two-wave mixing in media where the refractive índex is intensity dependent. This theoretical approach takes into account the saturation of the travelling population grating produced by two interesting beams (anharmonicities of the population grating) and the two-wave mixing process is regarded as the zero-order self-diffraction of the incident waves in this grating. The theoretical results are compared with the experimental ones and several theoretical predictions such as, the dependence of the probe gain parameter on the médium saturation intensity were experimentally verified

Neste trabalho, apresentamos uma extensão da técnica de varredura-Z baseada na análise espectral da evolução temporal da transmitância, quando um feixe laser é modulado numa freqüência f. As componentes de Fourier da evolução temporal da transmitância em f e 2f estão respectivamente relacionadas com os efeitos lineares e não-lineares e sua razão pode ser usada na eliminação de efeitos lineares. Este método, denominado varredura-Z resolvida em frequência, permite um aumento significativo na sensibilidade da técnica de varredura-Z em medidas de absorvedores lentos. Tal método se combinado com \"EZ-scan\" permite medidas de modulação de fase correspondentes a distorções da frente de onda de λ/105. A aplicabilidade bem como a sensibilidade desta técnica foram demonstradas em medidas realizadas em absorvedores lentos, especificamente o rubi e o aluminato de gadolínio dopado com cromo. Tais materiais são convenientes para estes fins, pois já tiveram suas não-linearidades investigadas anteriormente por diversos métodos. Como aplicação da técnica fizemos medidas das propriedades ópticas lineares e não-lineares em uma amostra de vidro fluoroindato dopado com cromo. Observamos que os valores de n2 (λ) seguem a curva de absorção desse material, e propomos um modelo que relaciona a origem da não-linearidade com as transições eletrônicas que ocorrem na região do visível. / This work presents an extension of the Z-scan technique based on the spectral analysis of the transmittance time-evolution when the laser beam is modulated at a frequency f. The Fourier components of the transmittance time-evolution at f and 2f are respectively related to the linear and nonlinear effects and their ratio can be used to eliminate spurious linear effects. This method, known as frequency resolved Z-scan, allows a significative increase in the sensitivity of the Z-scan technique for measurements of slow absorbers. When combined with the EZ-scan technique, it can measure transmittance changes corresponding to wavefront distortions of λ/105. The demonstration of the technique was carried out for slow absorbers, ruby and chromium-doped gadolinium aluminate. Such materials were conveniently chosen for this purpose since their optical nonlinearities are well stablished. As an application, we present linear and nonlinear optical properties of a chromium-doped fluorindate glass sample. We found that the values of n2 (λ) follow the absorption curve in this material and we have proposed a model which relates the origin of the nonlinearity with the electronic transitions that occur in the visible region of the spectrum.

Mistura de quatro ondas não degenerada em fibras ópticas na configuração de cavidade foi inicialmente proposto como forma de geração de estados comprimidos da luz. Neste trabalho desenvolvemos um tratamento pura- mente quântico da análise da interação não linear entre a luz e a matéria. Com a equação de Fokker-Planck na representação de Wigner obtemos di- retamente das equações o limiar de oscilação dos feixes gêmeos e o efeito de biestabilidade. Das equações de dinâmica linearizadas para as flutuações de quadraturas confirmamos a geração de estados comprimidos provenientes do processo de 4WM, tanto abaixo quanto acima do limiar de oscilação. Não é possível iniciar a geração dos feixes gêmeos sem antes alcançar o limiar de oscilação do espalhamento Brillouin estimulado. Portanto, técnicas para aumentar este limiar devem ser empregadas em qualquer medida de ruído ao nível de shot-noise com geração de campos. Nós também testamos as limitações técnicas intrínsecas do laser de diodo, como o ruído de amplitude e fase, assim como sua estabilidade em um experimento interferômetrico. Abaixo do limiar, a cavidade atua no sentido de reduzir o ruído de fase do laser em um intervalo de frequência que vai de 10MHz a 80MHz. / Nondegenarate four-wave mixing in an optical-fiber cavity geometry, was initially proposed as a mean to generate squeezed states of light. We developed in this work a purely quantum analyzis of the nonlinear interaction between light and medium. With Fokker-Planck equation in the Wigner representation, we obtained directly from the equations, the twin beams oscillation threshold and bistability. From the linearized dynamic equations for the quadratures fluctuations, we confirmed the generation of squeezed states proceeding from 4WM process, not only below but above the threshold oscillation. It is not possible to initiate the twin beams generation without first reaching the stimulated Brillouin scattering threshold. Therefore, techniques to increase this threshold, must be used for any noise measure to the shot-noise level with fields generation. We also have tested the technical limitations of laser diode, as amplitude and phase noise, as well as the stability in an interferometric experiment. Below threshold, the cavity acts in the sense of reducing the intrinsic laser phase noise in a frequency range that goes from 10MHz to 80MHz.

Apresentamos neste trabalho o procedimento de engenharia de dispersão em chips fotônicos compatíveis com tecnologia CMOS para conversão de frequências na escala de centenas de Terahertz em micro-ressoadores. Esses sistemas apresentam grande potencial para geração integrada de luz com propriedades não-clássicas para uso em ciência de informação quântica. Este é o primeiro trabalho que utiliza a dispersão dos modos transversos elétrico ou magnético de ordem-superiores para obter o comprimento de onda do zero de dispersão da velocidade de grupo em 795 nm. Demonstramos que, com um delicado balanço entre os termos de dispersão de segunda- e quarta-ordem, geramos dois feixes intensos que podem compartilhar informação quântica entre linhas atômicas e a banda de telecomunicação. / We present in this work the proceedings of dispersion engineering in CMOS compatible photonic chips for frequency conversion in the scale of hundreds of Terahertz in microresonators. These systems present great potential for integrated light generation with non-classical properties for use in quantum information science. This is the first work to use higher-order modes to obtain the zero dispersion wavelength close to 795 nm. We show that with a delicate balance between second- and fourth-order dispersion terms, two intense beams are generated that can possibly share quantum information between atomic lines and telecommunication band.

Neste trabalho estudamos as propriedades ópticas não lineares de aminoácidos utilizando pulsos de laser com duração de femtossegundos. O índice de refração não linear (n2) da L-alanina, L-prolina, L-serina, L-treonina e L-arginina em solução aquosa foram determinados. Foi também estudada a influência do pH na magnitude de n2 dos aminoácidos em solução. Paralelamente, determinamos a dispersão de n2 em cristais de L-treonina nos três eixos principais, x, y e z. Os aminoácidos têm despertado grande interesse devido as suas boas propriedades ópticas de segunda ordem. Todavia, suas propriedades ópticas de terceira ordem ainda não haviam sido estabelecidas. Além disso, implementamos a técnica de espalhamento hiper-Rayleigh para determinar a primeira hiperpolarizabilidade (P) de moléculas orgânicas, onde uma mudança foi introduzida para permitir medidas mais rápidas e com melhor precisão. Foram encontrados os valores de P de algumas porfirinas e corantes orgânicos. / In this work we have studied nonlinear optical properties of amino acids using femtosecond laser pulses. The nonlinear index of refraction (nz) of L-alanine, L-proline, L-serine, L-threonine and L-arginine in aqueous solution have been determined. Also, the influence of pH in the magnitude of nz of amino acids in solution has been studied. Besides, we have determined the n;, dispersion in the three main axis, x, y and z, in L-threonine crystals. The amino acids have attracted a great deal of attention due to their good second-order optical properties. However, their third-order optical properties had not been established yet. Furthermore, we have implemented the hyper-Rayleigh scattering technique to determine the first hyperpolarizability (P) of organic molecules, leading to fast and more precise measurements. It was found the P value of some porphyrins and organic dyes.