Nonlinear optics and ferroelectrics have been recognized for several decades as promising fields with important applications in the area of opto-electronics, photonics, memory devices, etc. High performance electro-optical switching elements for telecommunications and optical information processing are based on the material properties. Hence, there is always a continuous search for new and better materials. In this thesis we have investigated the growth and physical properties of four crystals viz. two NLO and two ferroelectric crystals. This thesis consists of eight chapters. The first chapter gives an overview of historical perspectives of nonlinear optical phenomenon, ferroelectricity and materials developed therein. The second chapter gives a brief description of the underlying theories of crystal growth, nonlinear optics and ferroelectricity. A major portion of this chapter consists of gist of the earlier work carried out on compounds of our interest viz. urea L-malic acid, sodium p-nitrophenolate dihydrate, glycine phosphite and lithium niobate. Synthesis, growth, crystal structure details and some physical properties of these materials are briefed. The third chapter describes the experimental techniques needed to grow as well as characterize these crystals. The experiments are performed on single crystals grown in the laboratory using the solution growth setup and Czochralski crystal puller. These growth units are described in detail. Preliminary characterization techniques like powder Xray diffraction, optical transmission, scanning electron microscopy, Vickers and Knoop hardness are described briefly. Various experimental methods viz. dielectric, polarization reversal, photoacoustic spectroscopy and laser induced damage for characterizing the grown crystals are explained. Urea L-malic acid (ULMA) is a new NLO organic material which is reported to exhibit second harmonic efficiency three times that of the widely used inorganic crystal, KDP. Hence, this material is selected for detailed investigation and the results obtained are discussed in chapter 4. This chapter contains details of single crystal growth and characterization of ULMA. The crystals are grown by slow cooling technique. The complete morphology of the crystal is evaluated using optical goniometry. The grown crystals are characterized for their optical and thermal properties. The defect content in the grown crystal is evaluated by chemical etching. As the surface damage of the crystal by high power lasers limits its performance in NLO applications, a detailed laser induced damage studies are performed on ULMA. Both single shot and multiple shot damage threshold values for 1064 nm and 532 nm laser radiation are determined and correlated with the mechanical hardness. In addition, the thermal diffusivity and thermal conductivity of ULMA along various crystallographic orientations are evaluated using laser induced photoacoustic spectroscopy and the results are interpreted in terms of crystal bonding environment. Another NLO crystal taken up for study is sodium p-nitrophenolate dihydrate (NPNa 2H2O), a semiorganic material. This crystal is a very efficient NLO material and has the advantages of both organics and inorganics. Earlier investigations on growth of NPNa.2H2O in various solvents have shown methanol as the most suitable solvent for growth. Growth from aqueous solution was discarded as it did not yield crystals which are stable. In the present investigation, stable, NLO active NPNa.2H2O crystals are obtained using aqueous solution itself by varying the crystallization conditions and exploring the suitable temperature range. The details of growth and characterization form the subject of fifth chapter. The grown crystals are characterized using optical transmission, XRD and thermo gravimetric analysis. Later, laser induced damage threshold is evaluated for both 1064 nm and 532 nm laser radiation and compared wit the methanol grown ones. A possible mechanism of damage is given. The sixth and seventh chapters deal with growth and characterization of ferroelectric materials namely glycine phosphite and lithium niobate respectively. Glycine phosphite is a low temperature ferroelectric crystal which is well studied in terms of its dielectric and ferroelectric properties. But very few radiation damage studies are reported. The effect of ionizing radiation on ferroelectrics is of considerable interest as it significantly modifies the physical properties of these materials. In the present investigation, effects of X-ray irradiation (_ = 1.5418 °A) on the lattice parameters, dielectric constant, loss tangent, polarization switching characteristics and domain dynamics of glycine phosphite are investigated. X-ray irradiation is performed in the non-polar phase of the sample. The effect as a function of duration of exposure is studied. X-ray irradiation in GPI has resulted in drastic reduction in _ values and shift in transition temperature towards lower temperatures. X-ray irradiation on polarization switching properties of the crystal are also investigated. The activation energy and threshold field of switching increase with the irradiation time. The behaviour of domain wall mobility is quite different from that exhibited by other well known ferroelectrics. These results are discussed in chapter 6 and a possible explanation for the unusual behaviour of domain wall mobility is given. The defect generated is identified as PO32− radical by electron paramagnetic measurement. Lithium niobate (LiNbO3) is an extensively studied material in terms of its NLO and ferroelectric properties. This material has high piezoelectric coupling coefficients along certain directions which makes it suitable for wide band surface acoustic wave applications. Hence there is a demand for good quality, single domain YZ-LiNbO3 substrates. Chapter 7 describes the growth of Z-pulled congruent LiNbO3 using Czochralski technique. Large single crystals of diameter 30 mm and length 80 mm are grown from congruent composition employing Czochralski technique. The grown crystals are multidomain and hence electric field poling is performed to get single domain crystals. Their subsequent characterization for SAW devices upto 200 MHz was performed and compared with the imported substrate. The general conclusions are given in chapter 8 along with possible future work that could be performed on these crystals.

This dissertation investigates two long standing issues in nonlinear optics: complete characterization of the ultrafast dynamics of simple molecules, and the potential of a two-photon laser using a bulk semiconductor gain medium. Within the Born-Oppenheimer approximation, nonlinear refraction in molecular liquids and gases can arise from both bound-electronic and nuclear origins. Knowledge of the magnitudes, temporal dynamics, polarization and spectral dependences of each of these mechanisms is important for many applications including filamentation, white-light continuum generation, all-optical switching, and nonlinear spectroscopy. In this work the nonlinear dynamics of molecules are investigated in both liquid and gas phase with the recently developed beam deflection technique which measures nonlinear refraction directly in the time domain. Thanks to the utility of the beam deflection technique we are able to completely determine the third-order response function of one of the most important molecular liquids in nonlinear optics, carbon disulfide. This allows the prediction of essentially any nonlinear refraction or two-photon absorption experiment on CS2. Measurements conducted on air (N2 and O2) and gaseous CS2 reveal coherent rotational revivals in the degree of alignment of the ensemble at a period that depends on its moment of inertia. This allows measurement of the rotational and centrifugal distortion constants of the isolated molecules. Additionally, the rotational contribution to the beam deflection measurement can be eliminated thanks to the particular polarization dependence of the mechanism. At a specific polarization, the dominant remaining contribution is due to the bound-electrons. Thus both the bound-electronic nonlinear refractive index of air, and second hyperpolarizability of isolated CS2 molecules, are measured directly. The later agrees well with liquid CS2 measurements, where local field effects are significant. The second major portion of this dissertation addresses the possibility of using bulk semiconductors as a two-photon gain medium. A two-photon laser has been a goal of nonlinear optics since shortly after the original laser*s development. In this case, two-photons are emitted from a single electronic transition rather than only one. This processes is known as two-photon gain (2PG). Semiconductors have large two-photon absorption coefficients, which are enhanced by ~2 orders of magnitude when using photons of very different energies, e.g., ћωa≈10ћωb. This enhancement should translate into large 2PG coefficients as well, given the inverse relationship between absorption and gain. Here, we experimentally demonstrate both degenerate and nondegenerate 2PG in optically excited bulk GaAs via pump-probe experiments. This constitutes, to my knowledge, the first report of nondegenerate two-photon gain. Competition between 2PG and competing processes, namely intervalence band and nondegenerate three-photon absorption (ND-3PA), in both cases are theoretically analyzed. Experimental measurements of ND-3PA agree with this analysis and show that it is enhanced much more than ND-2PG. It is found for both degenerate and nondegenerate photon pairs that the losses dominate the two-photon gain, preventing the possibility of a two-photon semiconductor laser.

In this study, two series of polymers based on benzobisthiazole were synthesized. The poly(benzobisthiazoles) (PBTs) have been synthesized by the solution polycondensation of 2,5-diamino-1,4-benzenedithiol in poly(phosphoric acid)s (PPA). The diacids used were systematically varied to find the best for the solubilization of the aromatic heterocyclic rigid-rod polymers. The role of PPA is identified and the effects of phosphorous pentoxide and water on PBT during polycondensation are discussed. Polymer properties such as the inherent viscosity, decomposition temperature are correlated to systematically varied diacids. Finally, the effect of diacid architecture on the synthesis and microstructure of PBT is studied. The results are further discussed in terms of resonance, symmetry, and solubilization of the diacids. Next, we extend the rigidity and resonance of benzobisthiazole for the application as second-order nonlinear optics. Novel nonlinear optical (NLO) polyimides containing benzobisthiazole chromophores have been synthesized. The soluble polyimides containing different ratios of carboxylic acids (COOH) were first prepared and the precursors of NLO chromophores reacted with those carboxylic acids, followed by the benzobisthiazole derived chromophores synthesized at 300 oC under vaccum. The formation of benzobisthiazole was evidenced by FTIR and UV-vis spectra in combination with the analysis of model polyimides. The excellent thermal properties of those NLO polyimides were examined by TGA and TMA. PI-1 shows thermal decomposition temperature as high as 554 oC at 10 wt % loss and a Tg of 324 oC. The amorphous morphology of those polyimides was verified by XRD traces and some ordered alignments were found, due to the rigidity of the benzobisthiazole derivatize chromophores. The electrooptic coefficient of PI-1 (r33 = 5.3 pm/V) was obtained.

In the paper, the beam propagation method is used to analyze the characteristics and the applications of nonlinear optical waveguide structures. The nonlinear optical waveguide is a medium whose refractive index changes with the electric field intensity. Based on the mode theory, the propagating envelop of optical light waves in the three-layers nonlinear waveguide with the nonlinear cladding, the nonlinear substrate and the linear guiding film can be solved. Not only the dispersion relation curve is described, but also the affection of input power to the electric field distribution is observed. In the application of nonlinear optical waveguide structure, the three-layers nonlinear waveguide structure and the local nonlinear Mach-Zehnder waveguide interferometer structure will be discussed: In the three-layers nonlinear waveguide structure, by launching the symmetric and antisymmetric modes, various characteristics of spatial optical solitons will be observed. Based on the interaction property between spatial optical solitons, a new all-optical 1¡ÑN switching device will be proposed; In the local nonlinear Mach-Zehnder waveguide interferometer structure, by fixing the input signal power and changing the control power, output signal beam will show the switching property. Besides, by changing the local nonlinear distributions, the nonlinear Mach-Zehnder interferometer will show various logic functions. The numerical results show that the proposed structures could function as all-optical switch devices and all-optical logic gates.

The aim of this diploma thesis is to study the optical properties of new -conjugated molecules based on 1,4-di(4'-N, N-diphenylaminostyryl)benzene and their potential application in advanced imaging techniques of biological specimens, the so-called multiphoton microscopy. The thesis focuses mainly on the characterization of their optical properties and the determination of their two-photon absorption cross-section using a unique laser equipment. Furthermore, a suitable methodology for the preparation of nanoparticles from these molecules, their characterization and stability are also developed. The thesis also investigates the influence of structure on the optical properties of these molecules. The relation between the length of the conjugated system and the presence of substituents on the backbone has been shown for the optical properties of the molecules in the solvent, the position and shape of the two-photon absorption spectrum and the value of two-photon absorption cross-section. It has been shown that this substance retains its unique fluorescent properties even in the form of nanoparticles and therefore appears to be a suitable candidate for the observation of biological specimens using multiphoton fluorescence microscopy. The work contributes to the knowledge base for the design of the chemical structure of molecules with desired properties.

The Silicon Wafer Integrated Fiber Technology, SWIFT, is a novel platform for the development of photonic devices. SWIFT is comprised of an optical fiber, specifically a D-fiber in this work, embedded into a V-groove etched into a silicon wafer. This provides a method to secure the fiber and allows the use of standard semiconductor industry equipment and techniques in latter processing for device fabrication. The SWIFT platform is used as the basis for the development of a polarimetric in-fiber electro-optic modulator. The modulator is based on the application of a nonlinear optical polymer, NLOP, film into the evanescent field of a D-fiber. In this way electric fields applied to the NLOP can be used to influence the light propagating through the fiber. The two initial processes in fabricating the modulator are accessing the evanescent field of the D-fiber and making a nonlinear optical polymer (NLOP) thin film. To expose the evanescent field the fiber is chemically etched using hydrofluoric acid. During the etching, light transmitted through the fiber is monitored for changes in power and polarization. The measured optical changes are correlated to scanning electron microscope images of the etched fibers to relate the etch depth to the changes in power and polarization. This provides an etching process that is controllable and repeatable. The NLOP films are made from a simple guest-host system based poly(methyl methacrylate) (PMMA) and dispersed red 1 azo dye (DR1), a nonlinear optical dye. The films are poled to align the dye molecules so that the polymer will exhibit nonlinear optical properties. The poled polymers are tested for second harmonic generation, SHG, to insure that they are nonlinearly optically active. Utilizing the SWIFT platform and the monitored etching process, fibers were etched to a desired 0.2 microns from the core on a repeatable basis. A nonlinear optical polymer was synthesized, formed into thin films, and poled. Nonlinear optical activity in the films was verified by SHG testing.

No description available.

No description available.

Molecular nonlinear optical (NLO) properties are extensively studied using both theory and experiment because of their use in myriad applications. Experimental measurements of the most interesting molecules’ NLO properties are difficult, so experimental data for molecules with desirable NLO properties is scarce. Theoretical tools don’t suffer from the same limitations and can provide significant insights into the physico-chemical phenomena underlying the nonlinear responses, can help in interpreting response behaviour of molecules, and can guide design the materials with desirable response properties. Here, I present my work on developing methods for accurately calculating the NLO properties of molecules using the finite field (FF) approach. The first chapter provides a background for the finite field and electronic structure methods used in this dissertation. Chapter two is a thorough investigation of the finite field method. The limitations of the method are highlighted and the optimal conditions for overcoming its drawbacks and obtaining meaningful and accurate results are described. Chapter three presents the first systematic study of the dependence of optimal field strengths on molecular descriptors. The first protocol for predicting the optimal field for the second hyperpolarizability is presented and successfully tested, and the dependence of the optimal field strength for the first hyperpolarizability on the molecular structure is investigated. Chapter four is an assessment of various DFT functionals in calculating the second hyperpolarizabilities of organic molecules and oligomers. This study shows the limitations of conventional DFT methods and the importance of electron correlation to response properties. In chapter five we present a new method of calculating NLO properties using a rational function model that is shown to be more robust and have lower computational cost than the traditional Taylor expansion. Finally, chapter six includes a summary of the thesis and an overview of future work. / Thesis / Doctor of Philosophy (PhD)

In this thesis, we investigate the nonlinear optical properties of four different physical systems: tellurite glasses, castor oil, ionic liquids and colloids of gold nanoparticles. Using Zscan and I-scan techniques, it was possible to determine the values of the electronic (n2 e) and thermal (n2 t) contributions of nonlinear refractive index of these systems as well as evaluating their respective thermo-optical coefficients (dn/dT). We use the I-scan technique to characterize five tellurite glass samples with different compositions. In this experiment we employ a Ti:sapphire laser operating in the modelocked regime, tuned at , delivering pulses, with a repetition rate that was controlled by a pulse selector. These glasses presented an ultra-fast self-focusing nonlinearity. The figure of merit 810 nm 200 fs 1kHz max 0 W= Δn λα was evaluated, and the condition was obtained for four of the five studied samples, displaying the potentiality of these glasses for ultra-fast all-optical switching applications, for example. Castor oil is a natural organic compound with a wide range of applications in industry. In the nanotechnology field, this oil has been exploited as very efficient dispersant and stabilizer agent for metallic gold nanoparticles in colloidal systems. However, a lack of data in literature concerning nonlinear optical properties of this material exists. In this work, we use the Z-scan technique to measure the nonlinear optical response of castor oil for laser excitation at 514 and 810 nm. In the visible region, the measurements had been carried out in the CW regime, using an Argon laser. In the infrared region, a Ti:sapphire laser, operating in the modelocked regime, producing pulses of 200 fs, with low (1 kHz) and high (76 MHz) repetition rate was employed instead. The castor oil presented a self-defocusing nonlinear refraction for both the laser wavelengths. The influence of the electronic and thermal contributions for nonlinearity was evaluated and the results indicate that the thermal effects are the main responsible for the observed nonlinear refraction. The thermo-optical coefficient ( ) of this compound was also measured for both wavelengths. We observe that castor oil thermo-optical coefficient is approximately an order of magnitude larger for the excitation tuned at 514 nm than at 810 nm. The nonlinear optical properties of two kinds of ionic liquids, BMI.BF4 and BMI.PF6, had been investigated. These materials are organic salts that present a low melting temperature and negligible vapor pressure. Although they have interesting physical-chemistry properties, and have been used in several applications, their nonlinear optical properties had been little investigated. In this work, we use the Z-scan technique at W > 0.27 dn / dT 514 nm and . Both ionic liquids displayed high self-defocusing nonlinearity, of thermal origin. We observed that the change of anion by anion modify the optical properties of these compounds. The ionic liquids had also presented a dispersion behavior in their thermo-optical coefficients in the spectral range studied. Although thermo-optical nonlinearities are a problem for the development of ultra-fast photonic devices, they can present a nonlocal character as a consequence of the process of heat conduction. Nonlinear effects in nonlocal media have been investigated in diverse branches of the physics, in particular in phenomena such as light pulses nonlinear propagation, as well as in generation and interaction of spatial solitons. Thus, these results suggest that castor oil and ionic liquids are promising candidates for investigation of nonlinear effects in nonlocal media. In the characterization of the colloidal systems of gold nanoparticles dispersed in castor oil, we evaluate the nonlinear refractive index, nonlinear absorption coefficient, as well as the thermo-optical coefficient in function of the filling factor f. Using Z-scan technique, for the laser excitation tuned at , we observe that the colloids presented an ultra-fast selfdefocusing refractive nonlinear response. Using the generalized Maxwell-Garnett model for composite materials it was possible to explain the behavior of the nonlinear refractive index of the colloid as a function of the filling factor, as well as estimate the value of the real part of the gold nanoparticles third-order nonlinear susceptibility. We also observe that the presence of gold nanoparticles dispersed in castor oil increased the absolute value of the linear absorption coefficient, the nonlinear refraction index of thermal origin and the thermo-optical coefficient. Our results indicate that the presence of gold nanoparticles modifies significantly local and nonlocal nonlinearities of a colloidal system. Moreover, the amount of nanoparticles is an extremely important factor for the development of new nanostructured materials aiming ultra-fast optical and nonlocal applications. 810 nm − 4 BF − 6 PF 800 nm / Fundação de Amparo a Pesquisa do Estado de Alagoas / Nesta tese, investigamos as propriedades ópticas não lineares de quatro sistemas físicos distintos: vidros teluretos, óleo de mamona, líquidos iônicos e colóides de nanopartículas de ouro. Utilizando as técnicas de varredura Z (Z-scan) e varredura de intensidade (I-scan) foi possível determinar os valores das contribuições de origem eletrônica (n2e) e térmica (n2t) do índice de refração não linear dos sistemas estudados, bem como avaliar os seus respectivos coeficientes termo-ópticos (dn/dT). Usamos a técnica de varredura de intensidade para caracterizar cinco amostras de vidros teluretos com diferentes composições. Neste experimento utilizamos um laser de Titânio de Safira operando no regime modelocked, sintonizado em , emitindo pulsos de de duração, com a taxa de repetição ajustada em através de um seletor de pulsos. Os vidros apresentaram uma não linearidade auto-focalizadora ultra-rápida. A figura de mérito 810 nm 200 fs 1 kHz max 0 W= Δn λα foi avaliada, ea condição foi obtida para quatro das cinco amostras estudadas, demonstrando a potencialidade destes vidros para aplicações em chaveamento totalmente óptico ultra-rápido, por exemplo. O óleo de mamona é um composto orgânico natural com uma ampla gama de aplicações na indústria. No campo da nanotecnologia, este óleo tem sido explorado como um agente dispersante e estabilizante muito eficiente para sistemas coloidais de nanopartículas metálicas de ouro. Entretanto, existe uma carência de dados na literatura acerca das propriedades ópticas não lineares deste material. Neste trabalho, utilizamos a técnica de varredura Z para medir a resposta óptica não linear do óleo de mamona para excitações em 514 nm e 810 nm. Na região visível, as medidas foram realizadas no regime CW, utilizando um laser argônio. No infravermelho, um laser de Titânio de Safira, operando no regime modelocked, produzindo pulsos de , com baixa ( ) e alta ( ) taxa de repetição foi utilizado. O óleo de mamona apresentou uma refração não linear autodesfocalizadora, em ambos os comprimentos de onda. A influência das contribuições eletrônica e térmica para a não linearidade medida foi avaliada e os resultados obtidos indicam que os efeitos térmicos são os principais responsáveis pela refração não linear observada. O coeficiente termo-óptico (W > 0,27 200 fs 1kHz 76 MHz dn dT ) deste composto também foi medido para os dois comprimentos de onda. Observamos que o dn dT do óleo de mamona é aproximadamente uma ordem de magnitude maior para a excitação sintonizada em 514 nm que em 810 nm. As propriedades ópticas não lineares de dois tipos de líquidos iônicos, BMI.BF4 e BMI.PF6, também foram investigadas. Estes materiais são sais orgânicos que se caracterizam por apresentar uma baixa temperatura de fusão e pressão de vapor desprezível. Apesar de possuir propriedades físico-químicas interessantes, e serem usados em diversas aplicações, suas propriedades ópticas não lineares foram pouco investigadas. Neste trabalho, usamos a técnica de varredura Z para excitação em 514 nm e 810 nm. Ambos os líquidos iônicos apresentaram uma grande não linearidade auto-desfocalizadora, de origem térmica. Observamos que a mudança do ânion pelo ânion modifica as propriedades ópticas destes compostos. Os líquidos iônicos também apresentaram uma dispersão nos seus coeficientes termo-ópticos no intervalo espectral estudado. Apesar de ser um problema para o desenvolvimento de dispositivos fotônicos ultra-rápidos, não linearidades termo-ópticas podem apresentar um caráter de não localidade como uma conseqüência do processo de condução de calor. Efeitos não lineares em meios não locais vêm sendo abordados em diversos ramos da física, em particular em fenômenos de propagação não linear de pulsos de luz, e na geração e interação de sólitons espaciais. Os resultados obtidos sugerem que tanto o óleo de mamona, quanto os líquidos iônicos são candidatos promissores para investigação de efeitos não lineares não locais. Na caracterização dos sistemas coloidais de nanopartículas de ouro dispersas em óleo de mamona avaliamos o índice de refração não linear, coeficiente de absorção não linear, bem como o coeficiente termo-óptico em função do fator de preenchimento f. Fazendo uso da técnica de varredura Z, para o laser de excitação sintonizado em , observamos que os colóides apresentaram uma resposta refrativa não linear autodesfocalizadora ultra-rápida. Utilizando o modelo de Maxwell-Garnett generalizado para materiais compostos foi possível explicar o comportamento do índice de refração não linear do colóide em função do fator de preenchimento, bem como estimar o valor da parte real da susceptibilidade não linear de terceira ordem das nanopartículas de ouro. Observamos também que a presença de nanopartículas de ouro dispersas no óleo de mamona aumentou o valor absoluto do coeficiente de absorção linear, do índice refração não linear de origem térmica e do coeficiente termo-óptico. Nossos resultados indicam que a presença de nanopartículas de ouro altera significativamente as respostas não lineares locais e não locais de um sistema coloidal. Desta forma, a quantidade de nanopartículas é um fator extremamente importante para o desenvolvimento de novos materiais nanoestruturados visando aplicações ópticas tanto ultra-rápidas, quanto não locais.