This research was mainly focused on the design and optimization of aperture-based structures to achieve the greatest third harmonic conversion efficiency. It was discovered that by tuning the localized surface plasmon resonance to the fundamental beam wavelength, and by tuning the propagating surface plasmons resonance to the Bragg resonance of the aperture arrays, both the directivity and conversion efficiency of the third harmonic signal were enhanced. The influence of the gap plasmon resonance on the third harmonic conversion efficiency of the aperture arrays was also investigated. The resulted third harmonic generation (THG) from an array of annular ring apertures as a closed loop structure were compared to arrays of H-shaped, double nanohole and rectangular apertures as open-loop structures. The H-shaped structure had the greatest conversion efficiency at approximately 0.5 %. Moreover, it was discovered that the maximum THG did not result from the smallest gap; instead, the gap sizes where the scattering and absorption cross sections were equal, led to the greatest THG. The finite difference time domain (FDTD) simulations based on the nonlinear scattering theory were also performed. The simulation results were in good agreement with the experimental data. Moreover, a modified quantum-corrected model was developed to study the electron tunneling effect as a limiting factor of the THG from plasmonic structures in the sub-nanometer regime. / Graduate / 0544 / 0794 / 0752 / 0756 / mrnezami@gmail.com

To Chi Wing = 具非線性光學性質客體-主體聚合物系統的極化動力學研究 / 杜志榮. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2006. / Includes bibliographical references (leaves 102-104). / Text in English; abstracts in English and Chinese. / by To Chi Wing = Ju fei xian xing guang xue xing zhi ke ti-zhu ti ju he wu xi tong de ji hua dong li xue yan jiu / Du Zhirong. / Table of contents / Acknowledgements --- p.ii / Abstract --- p.iii / Chinese Abstract --- p.iv / Table of Contents --- p.v / List of Figures --- p.viii / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Fundamental of nonlinear optics --- p.2 / Chapter 1.2 --- Centrosymmetry and even-order nonlinear susceptibilities --- p.4 / Chapter 1.3 --- Generation of second harmonic radiation --- p.5 / Chapter 1.4 --- Tensor properties of the nonlinear susceptibilities --- p.7 / Chapter 1.5 --- Relationship between macroscopic and microscopic nonlinear susceptibility for a poled polymer --- p.8 / Chapter 1.6 --- Outline of the thesis --- p.12 / Figures --- p.13 / Chapter Chapter 2 --- Poling and Relaxation of Guest-host Polymeric System --- p.15 / Chapter 2.1 --- Guest-host nonlinear optical polymeric systems --- p.15 / Chapter 2.1.1 --- Photoisomerization of Azobenzene --- p.16 / Chapter 2.1.2 --- Disperse Red-1 --- p.17 / Chapter 2.1.3 --- Poly (methyl methacrylate) --- p.18 / Chapter 2.2 --- Poling techniques --- p.19 / Chapter 2.2.1 --- Thermal Assisted Electric-field Poling --- p.19 / Chapter 2.2.2 --- Photo-assisted Electric-field poling --- p.22 / Chapter 2.2.3 --- All-Optical Poling --- p.25 / Chapter 2.3 --- Relaxation of poled nonlinear optical polymers --- p.27 / Figures --- p.31 / Chapter Chapter 3 --- Experimental Methods --- p.36 / Chapter 3.1 --- Sample Preparation --- p.36 / Chapter 3.2 --- Experimental Setup --- p.38 / Chapter 3.2.1 --- Laser system --- p.38 / Chapter 3.2.2 --- The reference arm --- p.39 / Chapter 3.2.3 --- The sample arm --- p.40 / Chapter 3.2.4 --- Data acquisition (DAQ) system --- p.41 / Chapter 3.2.5 --- Temperature control --- p.42 / Chapter 3.3 --- Poling and the erasing of thermal history --- p.43 / Chapter 3.3.1 --- All Optical Poling --- p.43 / Chapter 3.3.2 --- Eecteic Poling --- p.44 / Chapter 3.3.3 --- Erasure of thermal history --- p.45 / Figures --- p.46 / Chapter Chapter 4 --- Experimental results and discussions --- p.51 / Chapter 4.1 --- Reliability and reproducibility --- p.51 / Chapter 4.2 --- Features of different poling techniques --- p.52 / Chapter 4.2.1 --- Sub-Tg electric Poling --- p.53 / Chapter 4.2.2 --- Thermal assisted electric Poling --- p.54 / Chapter 4.2.3 --- Photo assisted electric Poling --- p.55 / Chapter 4.3 --- Relaxation of poling induced x(2) --- p.56 / Chapter 4.4 --- Effect of physical aging on the relaxation of PAP induced x{2) --- p.58 / Chapter 4.4.1 --- Origin of physical aging and its effect on relaxation --- p.58 / Chapter 4.4.2 --- Effect of aging on the relaxation of a PAP sample --- p.59 / Chapter 4.5 --- Onset studies of photo-induced free volume --- p.61 / Chapter 4.6 --- Comparative studies of TAP and PAP induced x{2) --- p.62 / Chapter 4.6.1 --- Secondary Poling --- p.63 / Chapter 4.6.1.1 --- Model for describing the temporal behavior of secondary poling --- p.65 / Chapter 4.6.1.2 --- Experimental details of the secondary poling measurement --- p.68 / Chapter 4.6.1.3 --- Results and Discussion on secondary poling of sample poled by TAP or PAP --- p.69 / Chapter 4.6.2 --- Onset of second harmonic signal during electric poling --- p.71 / Chapter 4.7 --- Charge injection studies --- p.73 / Figures --- p.77 / Chapter Chapter 5 --- Conclusion --- p.98 / References --- p.101

<p>Second harmonic generation (SHG) is a nonlinear optical effect sensitive to interfaces between materials with inversion symmetry. It is used as an effective tool for detection of the adsorption of a substance to microscopic particles, cells, liposomes, emulsions and similar structures, surface analysis and characterization of microparticles. The scattered second harmonic (SH) intensity from surfaces of suspended microparticles is characterized by its complex angular distribution dependence on the shape, size, and physical and chemical properties of the molecules making up the outer layer of the particles. In particular, the overall scattered SH intensity has been predicted to have a dramatic and nontrivial dependence on the particle size.</p><p>Results are reported for aqueous suspensions of polystyrene microspheres with different dye molecules adsorbed on their surfaces. They indicate that the scattered SH power has an oscillatory dependence on the particle size. It is also shown that adsorption of one of the dyes (malachite green) on polystyrene particles is strongly affected when SDS surfactants are added to the solution. For this system a rapid increase of the SH signal with increasing concentration of SDS was observed in the range of low SDS concentration.</p><p>Three different theoretical models are used to analyze the observed particle size dependence of SHG. The calculated angular and particle size dependences of the SH scattered power show that the models do not agree very well between each other when the size of the particles is of the order of the fundamental light wavelength, as here. One of the models - nonlinear Mie scattering - predicts oscillatory behaviour of the scattered SH power with the particle size, but fails to reproduce the position of the maxima and minima of the experimentally observed oscillations.</p><p>The obtained results on the size dependence of the SH can be used in all applications to increase the count rate by choosing particles of the size for which the SH efficiency was found to the highest. A new effect of cooperative malachite green and SDS interaction at the polystyrene surface can be employed, for example, in the areas of microbiology or biotechnology, where adsorption macromolecules, surfactants and dyes to polystyrene microparticles is widely used.</p>

Diamond-like semiconductors are interesting materials to study due to the wide variety of technologically useful properties that these materials possess. These normal valence compounds have structures that are based on that of diamond, either the cubic or hexagonal polymorph. Though there are a finite number of possible compounds, due to isovalent and isoelectronic principles, the total number of potential compounds is quite extensive. Quaternary diamond-like semiconductors provide a unique opportunity, because much of the previous research has focused on binary and ternary systems leaving quaternary systems, relatively unexplored. Additionally, quaternary diamond-like semiconductors possess a greater degree of compositional flexibility compared to binary and ternary materials, which could result in the ability to more carefully tune desired physical properties. &lt;br&gt;In order to prepare the new materials, Li2ZnGeS4, Li2ZnSnS4, Li2CdGeS4, Li2CdSnS4 and Ag2MnSnS4, several synthetic methods have been employed, including high-temperature solid-state synthesis, polychalcogenide flux synthesis and solid-state microwave synthesis. The solid-state microwave synthetic method was itself studied using a number of target systems such as the ternary diamond-like semiconductor, AgInSe2. Additionally, several intermetallic compounds, such as Ag3In, AuIn2 and Bi2Pd were prepared using this procedure. Solid-state microwave synthesis is not as well known as some of the other synthetic methods that were employed in this work possibly due to a lack of understanding of the method, training and equipment. Despite these problems, the method has the potential to save time, energy and cost due to the unique nature of microwave heating. In an attempt to gain a better understanding of this synthetic method and its capabilities, the solid-state microwave synthetic method was used to prepare diamond-like semiconductors and intermetallic compounds. / Bayer School of Natural and Environmental Sciences / Chemistry and Biochemistry / PhD / Dissertation

High Harmonic Generation (HHG) enables the production of bursts of coherent soft x-rays with attosecond pulse duration. This process arrises from the nonlinear interaction between intense infrared laser pulses and an ionizing gas medium. Soft x-ray photons are used for spectroscopy of inner-shell electron correlation and exchange processes, and the availability of attosecond pulse durations will enable these processes to be resolved on their natural time scales. The maximum or cutoff photon energy in HHG increases with both the intensity as well as the wavelength of the driving laser. It is highly desirable to increase the harmonic cutoff as this will allow for the generation of shorter attosecond pulses, as well as HHG spectroscopy of increasingly energetic electronic transitions. While the harmonic cutoff increases with laser wavelength, there is a corresponding decrease in harmonic yield. The first part of this thesis describes the experimental measurement of the wavelength scaling of HHG efficiency, which we report as lambda^(-6.3) in xenon, and lambda^(-6.5) in krypton. To increase the HHG cutoff, we have developed a 1.8 um source, with stable carrier envelope phase and a pulse duration of <2 optical cycles. The 1.8 um wavelength allowed for a significant increase in the harmonic cutoff compared to equivalent 800 nm sources, while still maintaing reasonable harmonic yield. By focusing this source into neon we have produced 400 eV harmonics that extend into the x-ray water window. In addition to providing a source of photons for a secondary target, the HHG spectrum caries the signature of the electronic structure of the generating medium. In krypton we observed a Cooper minimum at 85 eV, showing that photoionization cross sections can be measured with HHG. Measurements in xenon lead to the first clear observation of electron correlation effects during HHG, which manifest as a broad peak in the HHG spectrum centred at 100 eV. This thesis also describes several improvements to the HHG experiment including the development of an ionization detector for measuring laser intensity, as well as an investigation into the role of laser mode quality on HHG phase matching and efficiency.

Abstract: Nonlinear multicontrast microscopy is established in this study as an important tool for understanding biological structure and function of muscle cells. Second harmonic generation, third harmonic generation and multi-photon excitation fluorescence are acquired simultaneously in order to establish the origin of nonlinear signal generation in myocytes, and investigate myocyte structure and functionality during muscle contraction. Using structural cross-correlation image analysis, an algorithm developed specifically for this research, for the first time, third harmonic generation is shown to originate from the mitochondria in myocytes. The second harmonic, which is generated from the anisotropic bands of the sarcomeres, is further shown to be dependent on the crystalline order of the sarcomeres, thereby providing a potential diagnostic tool to evaluate disorder in muscle cells. The combination of the second and third harmonic provides complementary information that can be used to further elucidate the basic principles of muscle contraction. Time-lapse nonlinear microscopic imaging showed structural and functional dynamics in the myocytes. The second harmonic contrast revealed nonsynchronized nanocontractions of sarcomeres in relaxed, non-contracting, cardiomyocytes and Drosophila muscle samples, providing insight into the asynchronous behaviour of individual sarcomeres. Furthermore, macrocontracting samples were found to exhibit a synchronization of nanocontractions, providing new evidence for how muscles contract. Dynamic image correlation analysis, another algorithm developed specifically for this investigation, is used to reveal networks of mitochondria, which show fluctuations of multi-photon excitation fluorescence and third harmonic generation signals. The intensity fluctuations in the networks reveal both slow and fast dynamics; phase shifts of the slow dynamics between different networks are observed. Fast dynamics appear only in the inner networks, suggesting functional difference between interfibrillar and subsarcolemma mitochondria. The groundwork for studying bioenergetics of mitochondria in cardiomyocytes with nonlinear multimodal microscopy is fully developed in this work. The origin of the nonlinear signals and the development of the image analysis techniques provide a solid foundation to further study of muscle contractility and bioenergetics.

Conventional step-index silica fibers do not possess a second-order optical nonlinearity due to symmetry concerns. However, through the process of poling, the generation of a frozen-in DC field $E^{DC}$, and in turn, a non-zero second-order nonlinearity $\chi^{(2)} = 3\chi^{(3)}E^{DC}$, can be created in optical fibers. In this thesis, I measure the individual $\chi^{(2)}$ tensor elements of birefringent periodically poled fiber via second-harmonic generation and sum-frequency generation experiments. The symmetry of the $\chi^{(2)}$ tensor is consistent with that of the $\chi^{(3)}$ for isotropic media. This is the first study that characterizes all the $\chi^{(2)}$ tensor elements in birefringent poled fiber. Furthermore, I investigate the intermix of the $\chi^{(2)}$ tensor elements by twisting the fiber, which results in the generation of new second-harmonic signals not observed in untwisted fiber. The conversion efficiencies and spectral positions of these new signals can be varied by twisting the fiber.

The three wave mixing process was modeled in GaAs:AlGaAs superlattices using two new modeling tools that were developed in the course of this work: A 2D beam propagation tool for optimizing quasi-phase matching gratings, and a 1D iterative beam propagation tool for determining the output powers and threshold of optical parametric oscillators of arbitrary geometries. The 2D tool predicts close to 80% enhancement of conversion e ciency by phase matching near 800 nm compared to 775 nm, which was the originally designed operation wavelength. The model also predicts resonant behaviour for an abrupt grating pro le. The 1D tool was used to determine the threshold conditions for para- metric oscillation for di erent geometries. The performances of di erent phase matching approaches in AlGaAs were quantitatively compared. The model also indicated the need for pulsed operation to achieve reasonably low threshold powers in AlGaAs waveguides.

Conventional step-index silica fibers do not possess a second-order optical nonlinearity due to symmetry concerns. However, through the process of poling, the generation of a frozen-in DC field $E^{DC}$, and in turn, a non-zero second-order nonlinearity $\chi^{(2)} = 3\chi^{(3)}E^{DC}$, can be created in optical fibers. In this thesis, I measure the individual $\chi^{(2)}$ tensor elements of birefringent periodically poled fiber via second-harmonic generation and sum-frequency generation experiments. The symmetry of the $\chi^{(2)}$ tensor is consistent with that of the $\chi^{(3)}$ for isotropic media. This is the first study that characterizes all the $\chi^{(2)}$ tensor elements in birefringent poled fiber. Furthermore, I investigate the intermix of the $\chi^{(2)}$ tensor elements by twisting the fiber, which results in the generation of new second-harmonic signals not observed in untwisted fiber. The conversion efficiencies and spectral positions of these new signals can be varied by twisting the fiber.

The three wave mixing process was modeled in GaAs:AlGaAs superlattices using two new modeling tools that were developed in the course of this work: A 2D beam propagation tool for optimizing quasi-phase matching gratings, and a 1D iterative beam propagation tool for determining the output powers and threshold of optical parametric oscillators of arbitrary geometries. The 2D tool predicts close to 80% enhancement of conversion e ciency by phase matching near 800 nm compared to 775 nm, which was the originally designed operation wavelength. The model also predicts resonant behaviour for an abrupt grating pro le. The 1D tool was used to determine the threshold conditions for para- metric oscillation for di erent geometries. The performances of di erent phase matching approaches in AlGaAs were quantitatively compared. The model also indicated the need for pulsed operation to achieve reasonably low threshold powers in AlGaAs waveguides.