Choy Kwok Wai = 利用全光極化在本體聚合物中產生準相匹配二次諧波 / 蔡國偉. / Thesis submitted in: August 2005. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2006. / Includes bibliographical references (leaves 132-133). / Text in English; abstracts in English and Chinese. / Choy Kwok Wai = Li yong quan guang ji hua zai ben ti ju he wu zhong chan sheng zhun xiang pi pei er ci xie bo / Cai Guowei. / Acknowledgements --- p.ii / Abstract --- p.iii / Chinese Abstract --- p.V / Table of Contents --- p.vi / List of Figures --- p.ix / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Principle and origin of nonlinear optics --- p.2 / Chapter 1.2 --- Tensor properties and Inversion symmetry --- p.3 / Chapter 1.3 --- Relationship between microscopic and macroscopic nonlinear susceptibility for a poled polymer --- p.5 / Chapter 1.4 --- Second Harmonic Generation by nonlinear polarization --- p.7 / Chapter 1.5 --- Outline of the thesis --- p.9 / Figures --- p.10 / Chapter Chapter 2 --- Poling and relaxation of nonlinear optical polymeric systems --- p.11 / Chapter 2.1 --- Guest-Host nonlinear optical polymeric systems --- p.11 / Chapter 2.2 --- Poling techniques --- p.13 / Chapter 2.2.1 --- Thermal-assisted Electric Poling --- p.13 / Chapter 2.2.2 --- Photo-assisted Electric Poling --- p.15 / Chapter 2.2.3 --- All-optical Poling --- p.17 / Chapter 2.3 --- Quasi-phase-matching in bulk polymers by All-optical Poling --- p.20 / Chapter 2.4 --- Photorefractive effect in polymers --- p.22 / Chapter 2.5 --- Relaxation study of NLOP system --- p.23 / Figures --- p.27 / Chapter Chapter 3 --- Experimental Method --- p.33 / Chapter 3.1 --- Experimental Setup --- p.33 / Chapter 3.1.1 --- Laser system --- p.33 / Chapter 3.1.2 --- Data acquisition system --- p.34 / Chapter 3.1.3 --- Reference arm --- p.34 / Chapter 3.1.4 --- Optical Path --- p.35 / Chapter 3.2 --- Sample Preparation --- p.36 / Chapter 3.2.1 --- Polymer Films Preparation --- p.36 / Chapter 3.2.2 --- Bulk Polymers Preparation --- p.38 / Chapter 3.3 --- Poling and Thermal history of samples --- p.41 / Figures --- p.43 / Chapter Chapter 4 --- Growth and decay of optical nonlinearity in all-optically poled polymers --- p.53 / Chapter 4.1 --- Poling profiles for DR-1 and DANS doped bulk polymer by All-optical poling --- p.53 / Chapter 4.1.1 --- Poling profiles for DR-1 doped bulk polymer and polymer films by All-optical poling --- p.53 / Chapter 4.1.2 --- Possibilities of degradation of the samples during the experiment --- p.56 / Chapter 4.1.3 --- Effects of probing beam intensity and the duration of probing on the growth and decay of X(2) --- p.57 / Chapter 4.1.4 --- Poling profiles for DANS doped bulk polymer by All-optical poling --- p.57 / Chapter 4.2 --- Dependence of the poling profiles on various parameters in all-optical poling --- p.59 / Chapter 4.2.1 --- Dependence on the temperature --- p.59 / Chapter 4.2.2 --- Dependence on the relative intensities between the two seeding beams --- p.60 / Chapter 4.2.3 --- Dependence on the relative phase between the two seeding beams --- p.64 / Chapter 4.2.4 --- Tensorial properties of X(2) --- p.67 / Chapter 4.2.5 --- Dependence on the thickness of the sample --- p.68 / Chapter 4.3 --- Comparison of different relaxation models --- p.69 / Figures --- p.71 / Chapter Chapter 5 --- Growth and decay of optical nonlinearity in poled polymers with charge-generating additives --- p.89 / Chapter 5.1 --- Orientational enhancement in NLOP systems --- p.89 / Chapter 5.2 --- Space-charge field by charge-transporting molecules and sensitizer --- p.89 / Chapter 5.3 --- Poling profile of the bulk DR-1 polymer with charge-generating ingredients --- p.91 / Chapter 5.4 --- Poling profile of the bulk DANS polymer with the presence of charge-transporting molecules and sensitizers --- p.100 / Figures --- p.107 / Chapter Chapter 6 --- Growth and decay of optical nonlinearity in a nano-structured composite system --- p.113 / Chapter 6.1 --- Historical background --- p.113 / Chapter 6.2 --- Preparation of the composites films --- p.116 / Chapter 6.2.1 --- Preparation of the silver nano-particles --- p.116 / Chapter 6.2.2 --- Preparation of the composite films --- p.117 / Chapter 6.3 --- Poling profiles of polymer films with silver nano-particles --- p.118 / Figures --- p.124 / Chapter Chapter 7 --- Conclusions --- p.129 / References --- p.132

Lithium niobate (LiNbO3) and Lithium tantalate (LiTaO3) are high-performance nonlinear optical materials that have been popularly used in electro-optical modulation and nonlinear optics. Second-harmonic generation (SHG) microscope is applied to get SH images, as compared to etching method. SH image method has the advantage of faster and non-invasive inspection. Our system can rapid and non-destructive mapping of the detailed features of the crystal fibers in three dimensions. By simulation, we can explain that in the interface of +Z and ¡VZ domain, because the Li ions can stay in positive and negative two stable energy valleys. It may induce stronger SH intensity by QPM than +Z and -Z domain.

Optical second harmonic generation (SHG) is a nonlinear process that converts two photons of frequency w to a single photon of frequency 2w. In the electricdipole approximation, this process requires a noncentrosymmetric medium. For thin films present at the interface between two centrosymmetric media¡Ðsuch as the interface between two liquids, the interface between a liquid and air, or for the surface of a variety of insulators and semiconductors¡Ðonly the molecules which participate in the asymmetry of the interface contribute to the SHG. Surface SGH from molecules which exhibit a large nonlinear optical response at a specific wavelength can be used to measure the relative surface coverage of molecules at the interface as a function of the external electrochemical parameters. The polarization dependence of the surface SHG can be used to estimate the average molecular orientation of chromophores at the liquid/liquid electrochemical interface. The potential dependence of the SHG from the interface provides important information on the position of the adsorbed chromophores with respect to the interface.

Silicon nanocrystals (NCs), especially Si NCs embedded in SiO₂, have been studied intensely for decades for their potential application in silicon photonics, especially as efficient room temperature light emitters. Despite progress in fabricating photonic devices from Si NCs, the origin of the efficient photoluminescence (PL), the electronic and microscopic structure of the nanocrystals, and the structure of the elusive NC/SiO₂ interfaces for the oxide-embedded nanocrystals, remain controversial. Optical spectroscopy provides a powerful noninvasive tool for probing the structure of the Si NCs, including the active buried NC/SiO₂ interfaces of embedded particles. In this thesis work, oxide-embedded and free-standing alkyl-passivated silicon nanocrystals, prepared by different techniques, have been studied by linear and nonlinear optical spectroscopies. Cross-polarized 2-beam second-harmonic and sum-frequency generation (XP2-SHG/SFG) has been applied spectroscopically to study oxide embedded Si NCs of different sizes (3 to 5 nm diameter) and interface chemistries. The SHG/SFG spectra of silicon nanocrystals (Si NCs) prepared by implanting Si ions uniformly into silica substrates, then annealing, are compared and contrasted to their spectroscopic ellipsometric (SE) and photoluminescence excitation (PLE) spectra. Three resonances--two close in energy to E₁ (3.4 eV) and E2 (4.27 eV) critical-point resonances of crystalline silicon (c-Si), and a broad resonance intermediate in energy between E₁ and E₂--are observed in all three types of spectra. These features are observed in conjunction with a sharp 520 cm⁻¹ Raman peak characteristic of c-Si and an a-Si tail in the Raman spectra. The appearance of bulk-like CP resonances in the parallel PLE, SE and SHG/SFG spectra from Si NCs suggests the basic electronic structure of the bulk c-Si is preserved in nano-particles as small as 3 nm in diameter, albeit with significant size-dependent modification. At the same time, the prominence of a non-bulk-like resonance intermediate in energy between E₁ and E₂ CPs in all three types of spectra demonstrates the important contribution of nano-interfaces to the electronic structure.We also applied Raman spectroscopy to study oxide-embedded and oxide-free alkyl-passivated Si NCs with diameters ranging from 3 nm to greater than 10 nm synthesized by thermal decomposition of hydrogen silsesquioxane (HSQ). While oxide matrix complicates the size-dependence of the Raman peak shift for oxide-embedded nanocrystals, the Raman peak of the free-standing alkyl-passivated Si NCs shifts monotonically with NC size. / text

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Using a novel two-beam technique developed to greatly enhance quadrupolar contributions to the second-order nonlinear polarization, we performed a nonlinear spectroscopic study of silicon nanocrystals implanted in an SiO₂ matrix.

Implementation of the ultrasonic second harmonic generation has typically been restricted to simple setups such as through-transmission or Rayleigh surface waves. Recent research has evaluated the second harmonic generation in P- and SV- waves reflected from a stress-free surface to enable the single-sided interrogation of a specimen. This research considers the second harmonic generation in an aluminum specimen, which is analytically evaluated using an approach based on the perturbation method. Here, the model is chosen to mimic an experimental setup where a longitudinal wave is generated at an oblique angle and the reflected wave is detected using a set of wedge transducers. Due to mode conversion at the interface of the wedge and the specimen, it is necessary to evaluate longitudinal and shear waves, determining all second harmonic waves generated in the bulk and at the stressfree boundary. The theoretically developed model is then implemented in a commercial finite element code, COMSOL, using increasing fundamental wave amplitudes for different values of third order elastic constants. The results of this computational model verify the analytical approach and the proposed measurement setup, taking into account assumptions and approximations of the solution procedure. Furthermore, the computational model is used to draw important conclusions relevant to the experimental setup, including the need to avoid evolving surface waves and interactions with diffracted waves. These numerical results are used to develop a recommendation for the measurement position and incident angle. Finally, the nonlinearity of two different aluminum specimens is measured with the suggested measurement setup and the results confirm the feasibility of the single-sided determination of the acoustic nonlinearity using reflected bulk waves.

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.