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The development of efficient solar energy conversion devices has attracted much attention. Despite the fact that progress have been achieved, a fundamental understanding examining why efficiency can be improved remains elusive. For example, dye-sensitized solar cells (DSSC) exhibit high conversion efficiency when acetonitrile is used to prepare both the working electrode and the electrolyte. However, the mechanism explaining exactly how solvent influences device performance has not yet been systematically investigated. Another prominent example is the metal/semiconductor heterojunction systems. While it has been demonstrated that such mixed systems can significantly improve solar conversion efficiency, the mechanism of the electron dynamics driving these systems remains controversial. This stems in part from the fact that the experimentally deduced time constants, which are characteristic of such systems, are only ever extracted from phenomenological models and therefore cannot be assigned to specific physical processes. Ultimately, the development of a physical model is necessary to obtain an unambiguous physical picture of the solar conversion process. In this dissertation, the ultrafast nonlinear spectroscopic methods, second harmonic light scattering (SHS) and transient absorption (TA) spectroscopy, have been employed to study dye molecular adsorption and charge transfer dynamics in several solar energy conversion systems, including 1) DSSC, where solvent effects are investigated to understand why acetonitrile is the most effective solvent; 2) Ag/TiO2 heterostructure system, where a physical model is proposed to quantitively analyze the electron dynamics; 3) porphyrin/Ag/TiO2 nanocomposite, where we found there is no electron injection from porphyrin to TiO2 and plasmonic metal can enhance the porphyrin dye adsorption to improve the device efficiency. The propensity for surface adsorption of two related dyes, ortho-ethyl red (o-ER) and para-ethyl red (p-ER), onto TiO2 particles is studied with SHS. While p-ER readily adsorbs onto TiO2, o-ER does not. It is suggested that this difference is linked to the effects of the steric hindrance of the adsorbate. The influence of the solvent on the adsorption of p-ER onto TiO2 is also investigated. Of significance, p-ER can only chemically bond to the TiO2 surface in aprotic solvents, where adsorption free energy scales with solvent polarity. For protic solvents, preferential adsorption of the solvent shell ultimately prevents direct adsorption of p-ER onto the surface of TiO2. Likewise, solvent effects on charge transfer from p-ER to TiO2 are studied by TA. The electron injection rate is shown to be positively related to solvent polarity. Overall, highly polar aprotic solvents are shown to facilitate dye adsorption and electron injection, which helps improve the efficiency of DSSC devices. Ultrafast dynamics of plasmon-induced hot electrons from Ag to TiO2 nanorods are probed by TA. The observed transient signal, which corresponds to the lifetime of the optically generated electrons, is analyzed using a physical model including electron injection, relaxation, band edge annihilation, the surface to bulk diffusion, and back diffusion from the bulk to the surface. A ca. 13 fs electron injection time is deduced for Ag to TiO2, which is faster than that generated in Au and dyes. Additionally, the excited state exciton dynamics of a porphyrin J-aggregate are investigated and subsequently modeled. More rapid dynamics are found following aggregation of the porphyrin, which can be attributed to the inclusion of more efficient relaxation channels. However, no electron injection from the J-aggregate to TiO2 is observed. This likely stems from the negatively charged repulsion between the two components. Further, when the J-aggregate is introduced into an Ag/TiO2 system, optical excitation occurs predominantly in the J-aggregate. This stems either from direct excitation of the J-aggregate or indirect excitation through plasmon-induced resonant energy transfer from Ag. Our results indicate that plasmon can enhance the dye adsorption, which has great potential for designing more efficient plasmonic DSSC devices. / Chemistry

Nos últimos anos, materiais orgânicos tem ganhado grande interesse em áreas que envolvem espectroscopia óptica não linear. Isso se dá devido aos materiais possuirem consideráveis efeitos ópticos não lineares, apresentarem facilidade de síntese e possuirem propriedades fotofísicas e fotoquímicas que os tornam capazes de serem empregados em um vasto número de possíveis aplicações. Entre os materiais orgânicos, é possível destacar as Porfirinas e Ftalocianinas. A síntese desses materiais possibilita um grande número de classes ou grupos distintos, os quais podem ser distinguidos por suas estruturas periféricas e/ou íons metálicos que podem ser inseridos no interior dos macrociclos. Isso resulta em alterações das suas propriedades ópticas, ou seja, através de alterações das estruturas químicas das Porfirinas e Ftalocianinas é possível modelar suas propriedades ópticas, e assim, de acordo com essas propriedades, discriminar em quais aplicações podem ser empregados. Tais materiais, tendo em vista suas propriedades fotofísicas, podem ser empregados como fotossensitizadores na terapia fotodinâmica, células solares, limitadores ópticos ou fotobactericidas entre outras mais. Sendo assim, nesta Dissertação de Mestrado é realizado uma caracterização espectroscópica linear e não linear desses materiais, para assim deterinar propriedades ópticas específicas que podem ser empregadas nas aplicações citadas. Para tal caracterização espectroscópica, foram empregadas técnicas de espectroscopia linear e não linear, dentre elas a técnica de Varredura-Z foi empregada em três configurações distintas (Varredura-Z por Pulso Único, por Trem de Pulsos e por Luz Branca Supercontínua) para determinação de absorções de estados excitados. Tempos de vida de fluorescência, tempos de decaimento radiativo e de conversão interna, seções de choque de absorção de estado singleto e tripleto (fundamental e excitado) e eficiências quânticas (fluorescência, conversão interna e converção para tripleto) foram os parâmetros determinados e, assim, através desses parâmetros, foi possível entender como alterações nas estruturas químicas (periféricas e íons metálicos) influenciam consideravelmente as propriedades de Porfirinas e Ftalocianinas. / In last years, organic materials have won great interest in areas involving non-linear optical spectroscopy. This is due to the fact that the materials have considerable non-linear optical effects, are easy to synthesize, and have photophysical and photochemical properties that make them capable of being used in a wide range of possible applications. Among the organic materials, it is possible to highlight Porphyrins and Phthalocyanines. The synthesis of these materials enables a large number of distinct classes or groups, which can be distinguished by their peripheral structures and / or metal ions that can be inserted into the macrocycles. It results in changes of its optical properties, that is, replacing the chemical structures of such Porphyrins and Phthalocyanines, it is possible to tune its optical properties, and thus, according to these properties, to discriminate in which applications they can be used. Such materials, in view of their photophysical properties, can be used as photosensitizers in photodynamic therapy, solar cells, optical limiters or photobactericides among others. Thus, in this Master\'s Dissertation, a linear and nonlinear spectroscopic characterization of these materials is carried out in order to determine specific optical properties that can be employed in the cited applications. For this spectroscopic characterization, linear and nonlinear spectroscopy techniques were employed, among them the Z-Scan technique was employed in three distinct configurations (Z-Scan by Single Pulse, by Pulse Train and by Supercontinuum White Light) for determination of absorptions of excited states. Fluorescence lifetimes, radiative decay and internal conversion times, single and triple triplet (fundamental and excited) and quantum efficiencies (fluorescence, internal conversion, and triplet formation) were the parameters determined, and with these parameters, it was possible to understand how changes in the chemical structures (peripheral and metallic ions) modify considerable the optical properties of Porphyrins and Phthalocyanines.

Este trabalho propõe uma extensão do método de propagação de feixe (BPM - Beam Propagation Method) para a análise de guias de ondas ópticos e acopladores baseados em materiais não-lineares do tipo Kerr. Este método se destina à investigação de estruturas onde a utilização da equação escalar de Helmholtz (EEH) em seu limite paraxial não mais se aplica. Os métodos desenvolvidos para este fim são denominados na literatura como métodos de propagação de feixe de ângulo largo. O formalismo aqui desenvolvido é baseado na técnica das diferenças finitas e nos esquemas de Crank-Nicholson (CN) e Douglas generalizado (GD). Estes esquemas apresentam como característica o fato de apresentarem um erro de truncamento em relação ao passo de discretização transversal, &#916x, proporcional a O(&#916x2) para o primeiro e O(&#916x4). A convergência do método em ambos esquemas é otimizada pela utilização de um algoritmo interativo para a correção do campo no meio não-linear. O formalismo de ângulo largo é obtido pela expansão da EEH para os esquemas CN e GD em termos de polinômios aproximantes de Padé de ordem (1,0) e (1,1) para CN e GD, e (2,2) e (3,3) para CN. Os aproximantes de ordem superior a (1,1) apresentam sérios problemas de estabilidade. Este problema é eliminado pela rotação dos aproximantes no plano complexo. Duas condições de contorno nos extremos da janela computacional são também investigadas: 1) (TBC - Transparent Boundary Condition) e 2) condição de contorno absorvente (TAB - Transparent Absorbing Boundary). Estas condições de contorno possuem a facilidade de evitar que reflexões indesejáveis sejam transmitidas para dentro da janela computacional. Um estudo comparativo da influência destas condições de contorno na solução de guias de ondas ópticos não-lineares é também abordada neste trabalho. / This work introduces an extension of the beam propagation method (BPM) for the analysis of optical waveguides and couplers based on Kerr-type nonlinear materials. This method is intended for the investigation of structures where the paraxial scalar Helmholtz equation (EEH) no longer holds. The numerical methods developed for this situation are known in the literature as wide-angle beam propagation methods. The formulation developed in this work is based on finite differences and on the Crank-Nicholson (CN) and Generalized Douglas (GD) schemes. These schemes are characterized by a truncation error with respect to the transverse discretization step, &#916x, proporcional to O(&#916x2) for the CN and to O(&#916x4) for the GD scheme. The convergence of the method for both schemes is optimized by the application of an iterative algorithm for the correction of the field in the nonlinear medium. The wide-angle formalism is obtained by the expansion of the EEH for the CN and GD schemes in terms of Padé approximant polynomials. The expansions addressed in this work utilize Padé approximants of order (1,0) and (1,1) for the CN and GD scheme, and (2,2) and (3,3) for the CN scheme. Approximants orders higher than (1,1) show serious stability problems. This problem is circumvented by rotating the approximants in the complex plane. Two boundary conditions on the edge of the computational window are also investigated: 1) transparent boundary condition (TBC) and 2) transparent absorbing boundary (TAB). These boundary conditions are necessary in order to avoid unwanted reflections back to computational domain. A comparative study of the influence of these boundary conditions on the solution of nonlinear optical waveguides is also addressed in this work.

Femtosecond laser has been an essential tool for nonlinear optics and materials processing at micrometer scale, in which chalcogenide and heavy metal oxide glasses have received special attention not only for their high third-order optical nonlinearities but also due to their transparency up to the infrared regions. Although metallic nanoparticles are expected to improve the optical properties of glasses, there are no enough experimental researches about their influence on the nonlinear refractive index (n2) and nonlinear absorption coefficient (&#946), moreover at femtosecond regime. Based on the scientific and technological interests on highly nonlinear glasses, the goal of this thesis was to apply femtosecond laser pulses in two main domains: (i) at the basis of fundamental science, to study the effect of metallic nanoparticles in the third-order nonlinear optical properties of glasses; and (ii) at the field of applied science, aiming the development of photonic devices, performed by the fabrication of 3D optical waveguides containing metallic nanoparticles. This aim was achieved through the techniques of z-scan and femtosecond laser micromachining, which provided the nonlinear optical characterization and waveguides development, respectively. First, we analyzed the third-order nonlinear optical properties of the GeO2-Bi2O3 glass containing gold nanoparticles, which promoted saturation of the absorption in the region of the surface plasmon resonance band. On the other hand, these gold nanoparticles did not affect the n2 that kept constant in the wavelength range of 480 - 1500 nm. The same features were investigated for a Pb2P2O7-WO3 matrix doped with copper nanoparticles. In contrast to the gold doped ones, these samples showed a slight enhancement of the nonlinear refractive index when the energy of the excitation approaches the surface plasmon band. We also found out that the Pb2P2O7-WO3 matrix is a good host to grow silver nanoparticles by fs-laser micromachining. Similarly, copper nanoparticles were produced in a borosilicate glass using single-step laser processing. The explanation for metallic nanoparticle formation is addressed in this thesis, as well as, its application in waveguides. Thus, we demonstrated the functionality of optical waveguides containing Cu0 or Ag0 nanoparticles. Still based on the technological interests on glasses doped with nanoparticles, we showed a single-step synthesis of silver sulfide nanoparticles in chalcogenide glass, which was carried in partnership with researches at Princeton University. The materials investigated in this PhD work are of great importance for photonics, in which the synthesis of nanoparticles, fabrication of waveguides and nonlinear optical characterization have been performed. / O laser de femtossegundos tem sido uma ferramenta essencial tanto para a óptica não-linear quanto para o processamento de materiais na escala micrométrica, na qual os vidros calcogenetos e óxidos de metais pesados têm recebido atenção especial, não apenas pelas suas elevadas não-linearidades ópticas de terceira ordem, mas também devido à sua transparência até o infravermelho. Embora seja esperado que nanopartículas metálicas melhorem as propriedades ópticas dos vidros, não existe investigações experimentais suficientes sobre a sua influência no índice de refração não linear (n2) e no coeficiente de absorção linear (&#946), sobretudo no regime de femtossegundos. Com base nos interesses científicos e tecnológicos de vidros altamente não-lineares, o objetivo deste trabalho foi aplicar pulsos laser de femtossegundos em dois domínios principais: (i) na campo da ciência fundamental, para estudar o efeito de nanopartículas metálicas nas propriedades ópticas não lineares de terceira ordem destes materiais; e (ii) no domínio da ciência aplicada, visando o desenvolvimento de dispositivos fotônicos, realizado pelo fabricação de guias de onda tridimensionais contendo nanopartículas metálicas. Este objetivo foi alcançado através das técnicas de varredura-z e microfabricação com laser de femtossegundos, que proporcionaram a caracterização óptica não-linear e o desenvolvimento de guias de onda, respectivamente. Primeiramente, foram investigadas as propriedades ópticas não-lineares de terceira ordem do vidro GeO2-Bi2O3 contendo nanopartículas de ouro, as quais promoveram saturação da absorção na região da banda de ressonância de plásmon. Por outro lado, essas nanopartículas não afetaram o n2, que se manteve constante no intervalo de comprimento de onda 480 - 1500 nm. As mesmas características foram investigadas para uma matriz Pb2P2O7-WO3 dopada com nanopartículas de cobre. Em contraste com os vidros dopados com ouro, estas amostras apresentaram um ligeiro aumento do índice de refração não linear quando a energia de excitação está próxima da banda de ressonância de plásmon. Observou-se ainda que a matriz Pb2P2O7-WO3 é ideal para a obtenção de nanopartículas de prata através da microfabricação com laser de femtossegundos. Similarmente, nanopartículas de cobre foram produzidas em vidro de borosilicato usando somente uma varredura a laser. A explicação para a formação de nanopartículas metálicas é abordada nesta tese, bem como sua aplicação em guias de onda. Deste modo, demonstrou-se a funcionalidade de guias de onda ópticos compostos por nanopartículas de Cu0 e Ag0. Ainda com base nos interesses tecnológicos em vidros dopados com nanopartículas, demonstrou-se uma síntese de nanopartículas de sulfeto de prata em vidro calcogeneto usando o processamento de única etapa, realizada em parceria com pesquisadores da Universidade de Princeton. Os materiais investigados neste trabalho de doutorado são de grande importância para aplicações em fotônica, em que a síntese de nanopartículas, a fabricação de guias de onda e a caracterização óptica não-linear foram realizadas.

Le carbure de silicium (SiC) nanostructuré est considéré aujourd'hui comme une bonne alternative aux matériaux traditionnels pour diverses applications multidisciplinaires. Dans cette thèse, des nanostructures de SiC ont été élaborées par gravure électrochimique et par ablation laser. La première partie de cette thèse décrit et explique la dépendance en taille des propriétés optiques ainsi que l'importance des effets de champ local sur les transitions électroniques photo-induites des nanostructures de SiC. Dans la seconde partie, il est démontré une amplification d’un facteur 15 de l’intensité de photoluminescence des nanoparticules de SiC par leurs interactions en champ proche avec les plasmons multipolaires localisées. En outre, un facteur 287 et un facteur 72, induits par le couplage plasmonique, sont obtenus respectivement pour les signaux de luminescence à deux photons et de génération de seconde harmonique. Les principaux mécanismes physiques responsables des effets observés ont été décrits par des simulations de type différences finies dans le domaine temporel en trois dimensions. Enfin, l'effet de couplage de nanoparticules de SiC luminescentes à des nanostructures plasmoniques en structures planes est utilisé pour améliorer le marquage de cellules biologiques. Une perspective est ouverte sur la réalisation et les premières caractérisations de suspension colloïdales de nanohybrides plasmonique (Au@SiO2)SiC. / Nanostructured silicon carbide (SiC) is considered today as a good alternative to the conventional materials for various multidisciplinary applications. In this thesis, SiC nanostructures were elaborated by means of electrochemical etching and laser ablation techniques. The first part of the thesis clarifies size-dependence of optical properties as well as importance of local-field effects onto the photoinduced electronic transitions of SiC nanostructures. In the second part of the thesis strong 15-fold photoluminescence enhancement of SiC nanoparticles is ensured by their near-field interactions with multipolar localized plasmons. Further, 287-fold and 72-fold plasmon-induced enhancement factors of two-photon excited luminescence and second harmonic generation is achieved, respectively. The main physical mechanisms responsible for the observed effects were described by three-dimensional finite-difference time domain simulations. Finally, the coupling effect of luminescent SiC nanoparticles to plasmonic nanostructures is used in the enhanced labelling of biological cells on the planar structures. As a perspective, colloidal plasmonic (Au@SiO2)SiC nanohybrids were elaborated and characterized.

<p>Quantum chemical computations provide convenient and effective ways for molecular design using computers. In this dissertation, the molecular designs of optimal nonlinear optical (NLO) materials were investigated through three aspects. First, an inverse molecular design method was developed using a linear combination of atomic potential approach based on a Hückel-like tight-binding framework, and the optimizations of NLO properties were shown to be both efficient and effective. Second, for molecules with large first-hyperpolarizabilities, a new donor-carbon-nanotube paradigm was proposed and analyzed. Third, frequency-dependent first-hyperpolarizabilities were predicted and interpreted based on experimental linear absorption spectra and Thomas-Kuhn sum rules. Finally, molecular interferometers were designed to control charge-transfer using vibrational excitation. In particular, an ab initio vibronic pathway analysis was developed to describe inelastic electron tunneling, and the mechanism of vibronic pathway interferences was explored.</p> / Dissertation

This thesis is concerned with the material processing, photophysical and third-order nonlinear optical responses, and applications of a set of conjugated polymers in the telecommunication regions. Polyacetylene-based third-order nonlinear optical materials were chosen as candidates for all-optical signal and image processing. Substituted polyacetylenes were obtained using ring-opening metathesis polymerization of mono-substituted cyclooctatetraenes. Polymerization and processing conditions have been developed to generate thick, large-area films possessing large third-order nonlinearities in the telecommunication bands. The good optical quality of a 200 μm thick substituted polyacetylene film allowed for image correlation via off-resonant degenerated four-wave mixing with improved diffraction efficiency. Poly(2-methoxy-5-(2-ethyl-hexyloxy)-(phenylene vinylene)) (MEH-PPV) and (6,6)-phenyl-C61-butyric acid methyl ester (PCBM) composites showed strong nonlinear absorption and potential as optical limiters in the region of 700-900 nm. High optical quality, thick film of MEH-PPV:PCBM with the plasticizer dioctylphthalate (DOP) were made. Optical limiting of femtosecond and nanosecond pulses in the near infrared on these composites showed strong power suppression over a broad temporal regime. Femtosecond and nanosecond transient studies on the same thick MEH-PPV:PCBM:DOP composite films and the experimental results showed evidence for the photogeneration of radical ions as being responsible for the enhanced nonlinear absorption and strong optical suppression in the near infrared. Dithienopyrrole-based donor-acceptor copolymers with narrow bandgap showed strong nonlinear absorption and potential as optical limiters in the telecommunication wavelengths. Molecular engineering was applied to manipulate the spectral overlap of two-photon absorption and subsequent nonlinear absorptions. Femtosecond transient spectroscopy showed near infrared transient absorption and 22 - 61% yields of photogenerated charge-transfer species depending on donor-acceptor coupling strength. Torsional fluctuations of the backbone structure potentially affected the excited state behavior. Evidence suggests that ultrafast relaxation occurs to ground state and to long-lived charge-transfer state from the initially excited state. The dispersion of nonlinear absorption measured using the Z-scan method revealed large two-photon absorption cross sections of these polymers in the telecommunication region. Large suppression of nanosecond pulses at 1064 nm was achieved.

Present day advanced technologies heavily rely on one particular class of matter, i.e. the crystals. It is the periodic nature of the atoms and the properties arising due to the periodicity in crystals that is exploited to meet various technological feats. The technological revolutions in the semiconductor, optics and communication industries are the examples. The anisotropy in the crystals gives them enhanced properties as required in the field of non-linear optics. The field of non-linear optics became practically a reality after the invention of lasers. The coherent and monochromatic optical beams in the visible and ultraviolet ranges are in high demand due to their application in the fields like material processing, semiconductor lithography, laser micromachining, laser spectroscopy, photochemical synthesis, inertial confinement fusion and other basic scientific studies. In this thesis, work on the growth and characterization of two technologically important non-linear optical crystals has been carried out after developing the necessary instrumentation and some novel techniques for synthesis and growth. Also, studies on the glassy nature of one of the crystals have been carried out. This thesis consists of seven chapters. The first chapter gives a brief introduction to the nonlinear optical phenomenon, crystal growth and glassy state. Instrumentation is the backbone of crystal research technology. Without precision growth equipments large size crystals cannot be grown and without precision characterization instrumentation no conclusion regarding the quality and usefulness of the grown material can be drawn. The work reported in Chapter 2 describes the instrumentation developed for the growth, processing and characterization of crystals grown by solution and melt growth techniques. In low temperature solution growth, crystal growth workstations have been developed using tanks (made of acrylic), heating elements, and stirring propellers. Cooling coils have been inserted into the designed water bath to grow crystals below ambient also. This bath has an advantage to work over a wide range of temperatures, so that maximum retrieval of the material is possible. The growth of large crystals is usually hindered due to spurious nucleation precipitating during the growth process. A novel nucleation-trap crystallizer has been designed and developed that facilitates the continuation of the growth run in spite of extra nucleation precipitating after seeding. In this crystallizer, the spurious nuclei and any other particles generated after the filtration are forced into a well, and the growth of spurious nuclei is arrested by manipulating the temperature of this trap. Achieving adequate heat flow and mass flow profiles is of vital importance for growing good quality crystals. An optimized stirring procedure for the solution or melt is needed for ensuring the desired supply of growth units to the crystal-nutrient interface, and for transporting away any debris of the crystal-growth process. An ACRT set up has been designed and developed. For the growth of crystals by the flux technique and from direct melt, a crystal puller has been designed and developed. The crystal puller consists of a crystal rotation unit, slow and fast pulling mechanisms and a control unit. The pulling assembly is protected from damage caused by possible human errors through interlock mechanisms. The vibration at the shaft of the seed rotation assembly has been minimized by using a dc motor for rotation. A versatile triangular / square wave oscillator has been designed for developing a dc motor control. By implementing this control, the speed of the motor does not vary with supply-voltage variations. A quarter-step switching logic sequence is introduced for stepper motors, which is used for the slow UP/DOWN movement of the puller. This puller can be controlled locally by a control panel provided with the puller, or through a PC remotely by bypassing the local control. Additionally, for the processing and characterization of the grown DKDP crystals, a closed-loop thread-cutter, a ferroelectric loop tracer, and a computer-controlled system for measuring the half-wave voltage have been developed. A novel mercury encapsulant seeding technique that facilitates the processing of solution with immersed seed is invented and has been described in Chapter 3. This technique allows processing of solution with the seed inside the growth chamber, and still avoids contamination of the solution and formation of crystal clusters that are normally generated when seed is inserted after processing of the solution. DKDP and KAP crystal seeds have been used to check the dissolution of seeds, if any, when immersed in pure water for several hours and at high temperatures after introducing the seal. It has been observed that the mercury seal does not allow creeping of water into the seed holder, and there is no dissolution of the seed. This technique has been practically implemented for the growth of crystals from aqueous solution and its usefulness has been demonstrated by growing ammonium acid phthalate, potassium acid phthalate and potassium di-deuterium phosphate crystals. Nonlinear-optical crystals find major use in inertial-confinement fusion (ICF) experiments. For such applications, nonlinear crystals with very large damage-resistance are needed. Alternatively, crystals with moderate damage resistance but large size can be used for frequency-conversion for efficient plasma experiments. Potassium di-hydrogen phosphate, KH2PO4 (KDP) and its deuterated analog, K(DxH1-x)2PO4 (DKDP) are at present the only nonlinear optical crystals which can be grown to large sizes and are suitable for ICF studies. Also, solid-state light valves, light deflectors, and laser communication devices require large and perfect tetragonal DKDP crystals, with high deuterium concentration for easier operation. Chapter 4 describes the growth and characterization of DKDP crystals. DKDP crystals have been grown by all the three techniques i.e. conventional, platform and novel mercury encapsulant seeding techniques. Details about a new approach for the synthesis of DKDP solution have been given. A comparative study of the grown crystals by mercury-encapsulant technique and other techniques is described. Habit modification was observed due to the placement of seed crystals at an off-centre position and orientation in mercury encapsulant seeding technique and has been discussed. The grown crystals have been characterized for homogeneity, dislocations, transmission, DSC, rockng curve, etc. Due to the higher photon energies and the ability to be more tightly focused, coherent radiations of shorter wavelength (deep-UV) are in demand. The photon energies in this region are sufficient for bond-breaking processes in many materials, and find applications in fields like material processing, semiconductor lithography, laser micromachining, laser spectroscopy, photochemical synthesis, etc. Although excimer lasers (XeCl, KrF, ArF etc.) produce significant power in the deep-UV region, these laser systems involve corrosive gases, and are bulky, apart from requiring regular maintenance. A maintenance-free, compact, solid-state laser is preferable. But this, in turn, requires an efficient NLO crystal in that region. CLBO is one such crystal. Growth of CLBO crystals has been carried out by the flux-growth technique using B2O3-deficient flux, as well as from stoichiometric melt and has been discussed in Chapter 5. It was observed that the nucleation of material on platinum wire or spontaneous nucleation was difficult to achieve in spite of high supercooling. After forcing cracks into the mass deposited on platinum wire nucleation could be achieved. The growth of crystals was carried out on seeds with different orientations. Transmission studies, etch-pit studies and harmonic-generation experiments were performed on the grown crystals. The glass-forming tendency of CLBO has been studied and reported in Chapter 6. DTA experiments show that CLBO melt generally transforms to glass on cooling. Even at a cooling rate as low as 1°C/min, the material does not crystallize but transforms into glass. Ergodicity making and glass transition temperatures were determined for glassy CLBO. Since neither the crystallization peak nor the melting peak was observed in DTA experiments during the heating part of thermal cycle for glassy CLBO, a new approach of seeded crystallization was adopted in the calorimetric experiments to achieve crystallization. Since the size of added nuclei is already above the critical radius, the onset of crystallization peaks is independent of the critical-radius energy barrier. Kissenger method was applied to determine the activation energy of seeded- crystallization process. The transformation of glass CLBO to the crystalline phase is mediated by dendrites. Possibility of bulk crystal growth from the glassy state has been discussed, and a novel idea of surface crystallization is proposed. Chapter 7 summarizes the work carried out and projects the scope for future work.

Cancer is a world menace. After years of endeavor seeking the end of it, people started to realize that no matter how powerful the therapy could be, detection at early stage is always a cheaper, easier and more successful solution compared with curative methods for cancer developed onto its advanced stage. However, relatively few early-detection approaches have proven sufficiently effective and practical for mass use as a point-of-care tool. An early-cancer screening tool integrating the desired features of sensitive, informative, portable, and cost-effective is in need for the doctors. The progress in optical imaging and Micro-electro-mechanical system (MEMS) technology offers a promise for an innovative cancer screening alternative that is non-invasive, radiation-free, portable and potentially cost-effective. This dissertation investigates handheld instrumentation as multi-modalities of miniature imaging probes with various designs of MEMS devices, to obtain real-time images of epithelial tissue optical and physiological properties, combining the quantitative advantages of spectral analysis with the qualitative benefits of imaging to distinguish early cancer. This dissertation in sequence presents the handheld instruments in the fashions of Laser-scanning confocal microscopy (LSCM), optical diffuse reflectance imaging, nonlinear optical imaging modalities with their subsequent image-guided managements in oral cancer, skin cancer detection, circulating tumor cell (CTC) imaging, and imaging guided surgeries. One of the main challenges facing miniaturization lies in the mechanism of beam deflection across the sample. This dissertation introduces two generations of MEMS devices desgined, fabricated and incorporated in the imaging probes. A two-axis vertical comb driven silicon micromirror was used in the development of a handheld LSCM for oral cancer detection. Though obtaining numerous advantages, this first generation silicon MEMS micromirror suffers from small aperture size and high voltage requirement for actuation, which result in low collection efficiency in fluorescence imaging and medial safety concerns, respectively. Therefore a stainless steel scanner compatible with electrical discharge machining (EDM) process was fabricated with simplified process, low-voltage magnetic actuation and large fluorescence collection efficiency, with its capability demonstrated in the incorporation and embodiment of a handheld hyperspectral nonlinear imaging probe. Besides, software and controlling innovations for handheld imaging modalities are presented. A feedback controlling system for MEMS scanning status monitoring was developed for stabilized imaging rendering. For the sake of further improved imaging stability in handheld imaging and to enable on-site mosaic for large field viewing, a handheld mosaic system was developed and presented. / text