A dissertation submitted to the Faculty Of Science in partial fulfilment of the requirements for the degree of Master of Science by research only in the School of Physics, University of the Witwatersrand, Johannesburg. July 11, 2017. / A discrete Q-switched laser that gives a side-lobed single pulse as a laser output was implemented; followed by studying energy extraction e ciencies and pulse characterisation. The aim was to help design a passively Q-switched laser that gives a smooth single pulse of optimum energy as a laser output. The smoothness feature in a single pulse is important in some applications such as range nding. The concepts are demonstrated both experimentally and numerically; the latter using Fox-Li approach to modeling resonator modes with the Fresnel's integral for the system under study. In the rst two chapters, fundamentals of how a laser works and the spatial mode development are studied. In chapter 1, the principles of a laser are discussed: absorption, spontaneous and stimulated emission. Also, di erent types of pumping sources and resonator con gurations that can be used are discussed. In chapter 2, the focus is on developing spatial modes of a laser. The fundamental and high order modes are discussed together with their propagation laws. Then a numerical method is used to nd the eigenmodes of an arbitrary resonator con guration. This numerical method is used to simulate propagation of a fundamental mode and the simulation results are compared to analytical propagation laws. Then, this numerical method is used to simulate a laser resonator. The eigenmode of the lowest loss in the resonator was found. In chapters 3 and 4, experimental work is done on a Q-switched laser where the focus is on the overall laser performance. In chapter 3, Q-switched laser output energies are studied for di erent combinations of Q-switch transmission values and output coupler re ectivities. In addition, the in uence of spatial modes on a Q-switched pulse shape and pulse width are studied, taking into account beam divergence. In chapter 4, conclusions and future work are presented. In future work, the knowledge of spatial mode in uence on pulse shape, pulse width and beam divergence from chapter 3 is exploited. Then particular resonator con guration that gives optimised output results (Q-switched laser output energy, beam divergence, pulse shape and pulse width) is chosen. On that particular resonator, di erent Q-switch transmission values are studied, but now looking only at beam divergence and pulse width. Also, some suggestions on further improving laser performance are given. / LG2018

Chan Siu Wai = 利用二次諧波比較應用在非線性光學聚合材料上不同的極化技術 / 陳兆偉. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2003. / Includes bibliographical references (leaves 105-106). / Text in English; abstracts in English and Chinese. / Chan Siu Wai = Li yong er ci xie bo bi jiao ying yong zai fei xian xing guang xue ju he cai liao shang bu tong de ji hua ji shu / Chen Zhaowei. / Anknowledgements --- p.ii / Abstract --- p.iii / Chinese Abstract --- p.iv / List of figures --- p.v / Contents --- p.ix / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Formulation of nonlinear optics --- p.2 / Chapter 1.2 --- Relationship between microscopic and macroscopic nonlinear susceptibility for a poled polymer --- p.4 / Chapter 1.3 --- Generation of electromagnetic radiation by nonlinear polarization --- p.7 / Figure --- p.9 / Chapter Chapter 2 --- Poling of NLO polymer --- p.10 / Chapter 2.1 --- Doped NLO polymeric system --- p.10 / Chapter 2.2 --- Poling techniques --- p.13 / Chapter 2.2.1 --- Thermal´ؤassisted poling (TAP) --- p.14 / Chapter 2.2.2 --- Photoassisted poling (PAP) --- p.16 / Chapter 2.2.3 --- All-optical poling (AOP) --- p.20 / Chapter 2.3 --- Relaxation studies of poled NLO polymers --- p.22 / Figures --- p.26 / Chapter Chapter 3 --- Experimental methods --- p.32 / Chapter 3.1 --- Laser system --- p.32 / Chapter 3.2 --- Detection system --- p.33 / Chapter 3.3 --- Reference arm --- p.33 / Chapter 3.4 --- Experimental setup --- p.34 / Chapter 3.5 --- Samples preparation --- p.35 / Figures --- p.37 / Chapter Chapter 4 --- Growth and decay of optical nonlinearity In poled polymer --- p.42 / Chapter 4.1 --- Reliability and validity of the data acquisition procedures --- p.42 / Chapter 4.1.1 --- Temperature calibration and the voltage supply --- p.42 / Chapter 4.1.2 --- Possibilities of damage or degradation of the samples during the experiment --- p.43 / Chapter 4.1.3 --- Effect of probing beam intensity and the duration on the growth and decay of x(2) in A〇P --- p.44 / Chapter 4.2 --- Basic features of the different poling techniques --- p.45 / Chapter 4.2.1 --- Below Tg electric poling (EP) in the glassy state --- p.45 / Chapter 4.2.2 --- Thermal assisted poling (TAP) --- p.47 / Chapter 4.2.3 --- Photoassisted poling (PAP) in the glassy state --- p.49 / Chapter 4.2.3.1 --- Effects of polarization of the pumping light on photoinduced poling --- p.50 / Chapter 4.2.3.2 --- Comparison of photoassisted poling at 50°C and 75°C --- p.51 / Chapter 4.2.3.3 --- Can photoassisted poling work on DANS/PMMA sample? --- p.52 / Chapter 4.2.4 --- All-optical poling (AOP) in the glassy state --- p.53 / Chapter 4.3 --- Comparison of the relaxation of X(2) poled by the four poling techniques --- p.54 / Chapter 4.3.1 --- Methods in defining the relaxation curves --- p.54 / Chapter 4.3.2 --- "X(2) relaxation of DR-1/PMMA sample poled by EP, TAP, PAP and AOP" --- p.55 / Chapter 4.3.3 --- Comparison of the fitting of the relaxation data by different models --- p.57 / Figures --- p.59 / Chapter Chapter 5 --- Physical aging and its effect on the Poling stability --- p.73 / Chapter 5.1 --- Aging effect of samples poled by EP --- p.73 / Chapter 5.2 --- Aging effect of samples poled by TAP --- p.74 / Chapter 5.3 --- Aging effect of samples poled by PAP --- p.75 / Figures --- p.78 / Chapter Chapter 6 --- Results and discussions on other Observations --- p.86 / Chapter 6.1 --- Poling with TAP and PAP successively --- p.86 / Chapter 6.2 --- Secondary poling of EP/TAP processed NLO polymer --- p.88 / Chapter 6.3 --- Effect of a pumping green light on NLO polymer (DR-1/PMMA) in the glassy state --- p.90 / Chapter 6.4 --- Depoling effect by a pumping green light --- p.91 / Figures --- p.93 / Chapter Chapter 7 --- Conclusions --- p.102 / References --- p.105

by Chan Sung-Chun = 具有二階非線性光學性質的主體-客體多聚物系統中的載色體的動力學研究 / 陳崇真. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2004. / Includes bibliographical references (leaves 107-109). / Text in English; abstracts in English and Chinese. / by Chan Sung-chun = Ju you er jie fei xian xing guang xue xing zhi de zhu ti--ke ti duo ju wu xi tong zhong de zai se ti de dong li xue yan jiu / Chen Chongzhen / 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 --- Interaction of light with a medium --- 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.9 / Chapter 1.5 --- Outline of this thesis --- p.11 / Figures --- p.13 / Chapter Chapter 2 --- Poling and relaxation of Nonlinear Optical Polymeric systems --- p.14 / Chapter 2.1 --- Guest-Host nonlinear optical polymeric systems --- p.14 / Chapter 2.2 --- Poling of NLOP systems --- p.16 / Chapter 2.2.1 --- Thermal-assisted Electric Poling --- p.17 / Chapter 2.2.2 --- Photo-assisted Electric Poling --- p.19 / Chapter 2.2.3 --- All-Optical Poling --- p.22 / Chapter 2.3 --- Relaxation study of NLOP systems --- p.24 / Figures --- p.29 / Chapter Chapter 3 --- Experimental Method --- p.32 / Chapter 3.1 --- Sample Preparation --- p.32 / Chapter 3.2 --- Poling and Thermal history of samples --- p.35 / Chapter 3.3 --- Experimental Setup --- p.37 / Chapter 3.3.1 --- Laser system --- p.37 / Chapter 3.3.2 --- Data acquisition system --- p.37 / Chapter 3.3.3 --- Reference arm --- p.38 / Chapter 3.3.4 --- Optical Path --- p.39 / Figures --- p.43 / Chapter Chapter 4 --- Poling and relaxation studies of second order optical nonlinearity in a guest-host system --- p.50 / Chapter 4.1 --- Reliability and Reproducibility of the experimental result --- p.50 / Chapter 4.1.1 --- Temperature control --- p.50 / Chapter 4.1.2 --- Poling voltage --- p.51 / Chapter 4.1.3 --- Degradation of the sample --- p.52 / Chapter 4.1.4 --- Possible light induced decay by the probing laser beam --- p.53 / Chapter 4.2 --- Poling and relaxation in the Guest-Host system of DR-1/PMMA --- p.54 / Chapter 4.2.1 --- Poling in DR-l/PMMA --- p.54 / Chapter 4.2.2 --- Relaxation of polar orderin DR-l/PMMA --- p.58 / Chapter 4.3 --- Comparison of different relaxation models --- p.60 / Figures --- p.61 / Chapter Chapter 5 --- Investigation of chromophores dynamicsin poled nonlinear optical polymers by secondary poling --- p.69 / Chapter 5.1 --- Methods for studying the mobility of chromophores at sub-Tg temperature --- p.69 / Chapter 5.2 --- Experimental details --- p.71 / Chapter 5.3 --- Experimental results and discussion --- p.72 / Chapter 5.3.1 --- Free relaxation of chromophores --- p.72 / Chapter 5.3.2 --- Forced decay and further poling of chromophores --- p.73 / Chapter 5.4 --- Model for describing the temporal behavior of secondary poling --- p.76 / Chapter 5.4.1 --- Derivation of the model --- p.76 / Chapter 5.4.2 --- Quantitative description of the experimental results --- p.79 / Figures --- p.83 / Chapter Chapter 6 --- Results and observations on Photo-assisted electric poling --- p.89 / Chapter 6.1 --- Re-poling of the sample after PAP --- p.89 / Chapter 6.2 --- Other observations on Photo-assisted electric poling --- p.92 / Figures --- p.96 / Chapter Chapter 7 --- Conclusions --- p.103 / References --- p.107

No description available.

Thesis (Ph. D.)--Washington State University, December 2007. / Includes bibliographical references.

Thesis (Ph. D.)--University of Washington, 2006. / Vita. Includes bibliographical references (leaves 186-200).

Nonlinear optical phenomena associated with high-order soliton breakup in photonic crystal fibres and squeezed state generation in three dimensional photonic crystal microcavities are investigated. In both cases, the properties of periodically patterned, high-index contrast dielectric structures are engineered to control the dispersion and local field enhancements of the electromagnetic field. Ultra-short pulse propagation in a polarization-maintaining microstructured fibre (with 1 um core diameter and 1.1 m length) is investigated experimentally and theoretically. For an 80 MHz train of 130 fs pulses with average propagating powers in the fibre up to 13.8 mW, the output spectra consist of multiple discrete solitons that shift continuously to lower energies as they propagate in the lowest transverse mode of the fibre. The number of solitons and the amount that they shift both increase with the launched power. All of the data is quantitatively consistent with solutions of the nonlinear Schrodinger equation, but only when the Raman nonlinearity is treated without approximation, and self-steepening is included. The feasibility of using a parametric down-conversion process to generate squeezed electromagnetic states in 3D photonic crystal microcavity structures is investigated for the first time. The spectrum of the squeezed light is theoretically calculated by using an open cavity quantum mechanical formalism. The cavity communicates with two main channels, which model vertical radiation losses and coupling into a single-mode waveguide respectively. The amount of squeezing is determined by the correlation functions relating the field quadratures of light coupled into the waveguide. All of the relevant model parameters are realistically estimated using 3D finite-difference time-domain (FDTD) simulations. Squeezing up to ~20% below the shot noise level is predicted for reasonable optical excitation levels. To preserve the squeezed nature of the light generated in the microcavity, a unidirectional coupling geometry from the microcavity to a ridge waveguide in a slab photonic crystal structure is studied. The structure was successfully fabricated in a silicon membrane, and experimental measurements of the efficiency for the signal coupled out of the structure are in good agreement with the result of FDTD simulations. The coupling efficiency of the cavity mode to the output channel is ~60%.

Resonant or near resonant optical nonlinearities in semiconductor coupled quantum-well systems are discussed. Quantum engineered coupled or cascade quantumwell structures can provide giant nonlinear susceptibilities for various optical nonlinear processes. Nonlinearities integrated within quantum cascade lasers (QCL) showed great potential in various applications in the infrared range. Several schemes of nonlinearities are proposed and discussed in this work. Integrating difference frequency generation (DFG) with QCL can yield long wavelength radiation, such as terahertz light. The DFG process does not require population inversion at a transition associated with low photon energy; however, this requirement is necessary to lasers, such as QCL, and is hard to meet, because of the thermal backfilling and inefficient injection or pumping at room temperature. Therefore terahertz radiation due to DFG QCL for room temperature is proposed. On the other hand, the second harmonic generation can double laser frequency, and then push radiation frequency of AlInAs/GaInAs/InP based QCL to short wavelengths such as 3 μm and shorter. Optical nonlinearities can extend working frequencies of light sources, and also can help to improve light detection. For example, a sum frequency generation can upconvert mid/far-IR signal into near-IR signal with strong near-IR pump light, namely high efficient near-IR photon detector could be employed to detect mid/far-IR light. A specific designed quantum well structure of this frequency up-conversion scheme is discussed. A scheme of monolithic in-plane integration of the optical nonlinearities with QCL is also proposed. In this scheme, an optical nonlinear section is made from the same quantum well structure of a QCL, and is under an independent applied bias. Due to the independence of the applied bias, the nonlinearities can be tuned flexibly. In particular, a widely tunable Raman laser based on this scheme could be achieved. A frequency up-conversion based on sum frequency generation process in coupled quantum-well structure is also proposed for mid-infrared detection. By converting mid-IR signal to near-IR, superior near-IR detector such as silicon avalanche photo diode (APD) can be employed. The scheme can provide lower noise equivalent power (NEP) or higher detectivity compared with regular semiconductor photo detectors. A scheme of lasing without inversion (LWI) based on QCL for THz radiation is proposed. A ladder type three-level system for LWI process is integrated into a boundto- continue high power QCL at 10 μm. The proposed LWI generates THz signal at 69 μm. An optical gain about 80 cm-1 is achieved, against a waveguide loss about 30 cm-1 in a semi insulator (SI) surface plasmon waveguide.

The first hyperpolarizability £], which is an important factor in the second-order nonlinear optical effect, of the 5-6-5 heterocyclic rigid-rod chromophores-based derivatives has been systematically investigated in this work, applying the first principle based software CASTEP and the semi-empirical software MOPAC There are four factors chosen for this computational analysis, including the effects of (i) various rigid-rod molecules, (ii) auxiliary ability of various five-member rings, (iii) donor ability, and (iv) conjugation length. Results indicate that the benzobisimidazole (BBI)-based derivatives have larger £] values than those of benzobisthiazole (BBT) and benzobisoxazole (BBO)-based derivatives. The auxiliary donor ability of the pyrrole is larger than that of the thiophene and furan. In general, the £] value of various derivatives studied is parallel to the original donor strength and the trend in the donor is -N(CH3)2 > -NH2 > -OH > -CH3. In addition, the greater the conjugation length in the derivatives is, the higher the £] value. Further, from the analyses on the band-resolved £] values and the orbital density figures, it is found that the major contribution to the enhanced £] comes primarily from an efficient charge transfer from the donor side via the intermediate heterocyclic bridge to the acceptor side. Finally, a comparison between CASTEP and MOPAC reveals that CASTEP is more appropriate and accurate in predicting the optical properties of the heterocyclic-ring-based derivatives.

Nonlinear optical phenomena associated with high-order soliton breakup in photonic crystal fibres and squeezed state generation in three dimensional photonic crystal microcavities are investigated. In both cases, the properties of periodically patterned, high-index contrast dielectric structures are engineered to control the dispersion and local field enhancements of the electromagnetic field. Ultra-short pulse propagation in a polarization-maintaining microstructured fibre (with 1 um core diameter and 1.1 m length) is investigated experimentally and theoretically. For an 80 MHz train of 130 fs pulses with average propagating powers in the fibre up to 13.8 mW, the output spectra consist of multiple discrete solitons that shift continuously to lower energies as they propagate in the lowest transverse mode of the fibre. The number of solitons and the amount that they shift both increase with the launched power. All of the data is quantitatively consistent with solutions of the nonlinear Schrodinger equation, but only when the Raman nonlinearity is treated without approximation, and self-steepening is included. The feasibility of using a parametric down-conversion process to generate squeezed electromagnetic states in 3D photonic crystal microcavity structures is investigated for the first time. The spectrum of the squeezed light is theoretically calculated by using an open cavity quantum mechanical formalism. The cavity communicates with two main channels, which model vertical radiation losses and coupling into a single-mode waveguide respectively. The amount of squeezing is determined by the correlation functions relating the field quadratures of light coupled into the waveguide. All of the relevant model parameters are realistically estimated using 3D finite-difference time-domain (FDTD) simulations. Squeezing up to ~20% below the shot noise level is predicted for reasonable optical excitation levels. To preserve the squeezed nature of the light generated in the microcavity, a unidirectional coupling geometry from the microcavity to a ridge waveguide in a slab photonic crystal structure is studied. The structure was successfully fabricated in a silicon membrane, and experimental measurements of the efficiency for the signal coupled out of the structure are in good agreement with the result of FDTD simulations. The coupling efficiency of the cavity mode to the output channel is ~60%.