Doctor of Philosophy / Department of Physics / Vinod Kumarappan / In this thesis, our work on developing new techniques to measure and enhance field-free molecular alignment and orientation is described. Non-resonant femtosecond laser pulses are used to align and orient rotationally-cold gas-phase molecules. The time-dependent Schrodinger equation is solved to simulate the experimental results. A single-shot kHz velocity map imaging (VMI) spectrometer is developed for characterizing 1D and 3D alignment. Stimulated by a novel metric for 3D alignment proposed by Makhija et al. [Phys. Rev. A 85,033425 (2012)], a multi-pulse scheme to improve 3D alignment is demonstrated experimentally on difluoro-iodobenzene molecules and the best field-free 3D alignment is achieved. A degenerate four wave mixing probe is developed to overcome limitations in VMI measurement; experiments on different types of molecules show good agreement with computational results. Highly aligned linear molecules are used for high harmonic generation experiments. Due to the high degree of alignment, fractional revivals, variation of revival structure with harmonic order and the shape resonance and Cooper minimum in the photoionization cross section of molecular nitrogen are all observed directly in experiment for the first time. Enhanced orientation from rotationally cold heteronuclear molecules is also demonstrated. We follow the theory developed by Zhang et al. [Phys. Rev. A 83, 043410 (2011)] and demonstrate experimentally for the first time that for rotationally cold carbon monoxide an aligning laser pulse followed by a two-color laser pulse can increase field-free orientation level by almost a factor of three compared to using just the two-color pulse.

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

Charge trapping dynamics in Si/SiO2/Hf(1-x)SixO2 and III-V film stack systems are characterized using spectroscopic ellipsometry (SE) and second harmonic generation (SHG). For the first time, discrete absorption features within the bandgap of the SiO2 interfacial layer are identified using SE, and their relation to both intrinsic and process-induced defects is proposed. Sensitivity of the absorption features to process conditions is demonstrated and evidence that these defects contribute to Vfb roll-off is presented. Defects in the Hf(1-x)SixO2 films are probed with fs laser-induced internal multi-photon photo-excitation (IMPE) and time dependent electrostatic field induced second harmonic (TD-EFISH) generation. For the as deposited HfO2 films, a unique TD-EFISH response is identified and explained by resonant two photon ionization of a specific point defect and subsequent tunneling of the photoelectrons to the Si substrate. Charge trapping kinetics for all Hf(1-x)SixO2 films are investigated. Two characteristic trap cross sections are identified and found to be insensitive to dielectric film and process conditions, and associated with a surface “harpooning” mechanism. EFISH from non-centrosymmetric III-V media, including GaAs and In0.53Ga0.47As, is also studied. The anisotropic and time dependent SHG response from different chemically treated In0.53Ga0.47As surfaces is clearly distinguishable and associated with a process-induced change in the surface depletion field. / text

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. 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. 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. 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.

No description available.

Chiral molecules, which exist under enantiomers with non-mirror-symmetrical structures, have been the subject of intense research for their linear and nonlinear optical activities. Cysteine is such a chiral amino acid found as a building block of proteins throughout human bodies. Second harmonic generation (SHG) has been considered to investigate chiral molecules. SHG from metallic nanoparticles is promising for nanoplasmonics and photonic nanodevice applications. Therefore, it’s desirable to combine and study nonlinear properties due to both chirality and metallic nanoparticles, and help developing an alternatively optical diagnostic of chiral molecules. Our experiments are carried out with the FemtoFiber Scientific FFS laser system. SHG of silver nanoparticles (Ag NPs) modified by either L-Cysteine (L-C) or D-Cysteine (D-C) is observed, where L-Cysteine and D-Cysteine are a pair of enantiomers. Ag NPs are deposited through Vacuum Thermal Evaporation, controlled under different deposition thicknesses. UV-Vis/IR spectra and AFM are used to characterize Ag NPs under different conditions. Transmitted SHG measurements dependent on incidence are recorded with standard lock-in techniques. Deposition thickness of vacuum thermal evaporation plays an important role in forming diverse Ag NPs, which strongly imparts the intensity of SHG. Second harmonic intensity as a function of the incident angle presents similar results for Ag NPs with or without L-Cysteine or D-Cysteine modification, in the output of p- and s-polarization. However, we monitor reversed rotation difference in second harmonic intensities at linearly +45° and -45° polarization for L-C/Ag NPs and D-C/Ag NPs, while there’s no difference at linearly +45° and -45° polarization for Ag NPs alone. This optical rotation difference in SHG is termed as SHG-ORD. Also, for second harmonic light fixed at p-polarization, L-C/Ag NPs and D-C/Ag NPs exhibit a reversely net difference for SHG excited by right and left circular polarization, which is termed as SHG-CD. Experiments on SHG-ORD of chiral-modified Ag NPs by a mixture of L-Cysteine and D-Cysteine further help verifying the existence of chirality in chiral-modified Ag NPs. As a conclusion, SHG efficiently probed and distinguished L-Cysteine from D-Cysteine in chiral-modified Ag NPs. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2013-09-29 21:27:23.112

Doctor of Philosophy / Department of Physics / Chii-Dong Lin / Isolated attosecond pulse (IAP) is a tool of probing electronic dynamics occurring in atoms, molecules, clusters and solids, since the time scale of electronic motion is on the order of attoseconds. The generation, characterization and applications of IAPs has become one of the fast frontiers of laser experiments. This dissertation focuses on several aspects of attosecond physics. First, we study the driving wavelength scaling of the yield of high-order harmonic generation (HHG) by applying the quantum orbit theory. The unfavorable scaling law especially for the short quantum orbit is of great importance to attoseond pulse generation toward hundreds of eVs or keV photon energy region by mid-infrared (mid-IR) lasers. Second, we investigate the accuracy of the current frequency-resolved optical gating for complete reconstruction of attosecond bursts (FROG-CRAB) and phase retrieval by omega oscillation filtering (PROOF) methods for IAP characterization by simulating the experimental data by theoretical calculation. This calibration is critical but has not been carefully carried out before. We also present an improved method, namely the swPROOF which is more universal and robust than the original PROOF method. Third, we investigate the controversial topic of photoionization time delay. We find the limitation of the FROG-CRAB method which has been used to extract the photoionization time delay between the 2s and 2p channels in neon. The time delay retrieval is sensitive to the attochirp of the XUV pulse, which may lead to discrepancies between experiment and theory. A new fitting method is proposed in order to overcome the limitations of FROG-CRAB. Finally, IAPs are used to probe the dynamic of electron correlation in helium atom by means of attosecond transient absorption spectroscopy. The agreement between the measurement and our analytical model verifies the observation of time-dependent build up of the 2s2p Fano resonance.

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>