This work concerns the vacuum deposition of novel thin films that exhibit nonlinear optical effects due to their unusual microstructure. We discuss four different materials: 1) Tilted columns of aluminum-oxide 2) Gold particles in aluminum-oxide 3) Cadmium sulpho-selenide particles in aluminum-oxide 4) Silver particles in zinc-sulphide. We begin with a description of the vacuum system and some the techniques used to characterize the optical and structural properties of the films. This leads to our study of second-harmonic generation (SHG) in aluminum-oxide thin films deposited at an angle to the evaporant source. We show that SHG is very sensitive to the non-isotropic microstructure that results from such a deposition. and the behavior of the SHG signal with sample orientation provides insight to the symmetry properties of the microstructure. In a related study we show that AU/Al₂O₃ composite films produce a large SHG signal. We investigate the dependence of the strength of the SHG signal with fill-fraction of gold and show that it increases quadratically. in agreement with theory. The third material we discuss is cadmium sulpho-selenide doped aluminumoxide. We describe attempts at nucleating semiconductor crystallites in a variety of hosts through a process of co-deposition and subsequent annealing. We also deposit alternate layers of CdS-Se and Al₂O₃ with the semiconductor layer thin enough that interspersed crystallites form. This results in suspended. isolated crystallites similar to the doped-glass materials of interest to nonlinear optics. A waveguide of a CdS/Al₂O₃ "sandwich" demonstrates optical nonlinearity through a power-dependent prism coupling experiment, and the degree of nonlinearity is much greater than undoped glass, though less than doped glass. The final section of the dissertation is a theoretical description of nonlinear optical behavior in a novel composite material consisting of metal particles in a nonlinear dielectric host. We assume the enhanced field around the resonating particles drives the host locally nonlinear through either a Kerr-type or thermal nonlinearity. We calculate the change in optical properties of the medium due to this effect and show that for a system of silver in zinc-sulphide the nonlinearity can be significant.

Two spectral regions of gain exist for a weak probe beam propagating through a medium of two-level-atoms pumped by a strong near-resonance field. Experimentally a cw ring-dye laser is used to explore this gain at the Na D₂ resonance in a vapor. Plane-wave calculations of probe-gain spectra which include the Doppler broadening inherent in a vapor agree well with experimental spectra obtained with a Fabry-Perot interferometer. Such two-beam-coupling gain might have applications as optical pre- or power amplifiers. The gain is also the primary step in four-wave-mixing. Mixing of the pump and sideband which experiences gain produces the medium polarization from which the fourth-wave arises. For phase-matched propagation the fourth-wave, which is at a frequency that experiences little or negative probe-gain (i.e., absorption), grows at nearly the same rate as the primary sideband. Together the two sidebands extract far more than twice as much energy from the pump than does the primary sideband acting alone. Experimentally four-wave-mixing which arises from noise at the gain-sideband-frequency is sometimes accompanied by conical emission at the fourth-wave sideband. Since this sideband is also seen on axis the explanation cannot be simply phase-matching. Simulations which include the full transverse nature of the experiment are currently running on a CRAY supercomputer. These simulations indicate that the radial variation of the medium index of refraction is responsible for conical emission.

<p>The nonlinear interaction between light and atoms is an extensive field of study with a broad range of applications in quantum information science and condensed matter physics. Nonlinear optical phenomena occurring in cold atoms are particularly interesting because such slowly moving atoms can spatially organize into density gratings, which allows for studies involving optical interactions with structured materials. In this thesis, I describe a novel nonlinear optical effect that arises when cold atoms spatially bunch in an optical lattice. I show that employing this spatial atomic bunching provides access to a unique physical regime with reduced thresholds for nonlinear optical processes and enhanced material properties. Using this method, I observe the nonlinear optical phenomenon of transverse optical pattern formation at record-low powers. These transverse optical patterns are generated by a wave- mixing process that is mediated by the cold atomic vapor. The optical patterns are highly multimode and induce rich non-equilibrium atomic dynamics. In particular, I find that there exists a synergistic interplay between the generated optical pat- terns and the atoms, wherein the scattered fields help the atoms to self-organize into new, multimode structures that are not externally imposed on the atomic sample. These self-organized structures in turn enhance the power in the optical patterns. I provide the first detailed investigation of the motional dynamics of atoms that have self-organized in a multimode geometry. I also show that the transverse optical patterns induce Sisyphus cooling in all three spatial dimensions, which is the first observation of spontaneous three-dimensional cooling. My experiment represents a unique means by which to study nonlinear optics and non-equilibrium dynamics at ultra-low required powers.</p> / Dissertation

Lasers are an essential technology enabling countless fields of optics, however, their operation wavelengths are limited to isolated regions across the optical spectrum due to the need for suitable gain media. Parametric frequency conversion (PFC) is an attractive means to convert existing lasers to new colors using nonlinear optical interactions rather than the material properties of the host medium, allowing for the development of high power laser sources across the entire optical spectrum. PFC in bulk χ(2) crystals has led to the development of the optical parametric oscillator, which is currently the standard source for high power light at non-traditional wavelengths in the laboratory setting. Ideally, however, one could implement PFC in an optical fiber, thus leveraging the crucial benefits of a guided-wave geometry: alignment-free, compact, and robust operation. Four-wave mixing (FWM) is a nonlinear effect in optical fibers that can be used to convert frequencies, the major challenge being conservation of momentum, or phase matching, between the interacting light waves. Phase matching can be satisfied through the interaction of different spatial modes in a multi-mode fiber, however, previous demonstrations have been limited by mode stability and narrow-band FWM gain. Alternatively, phase matching within the fundamental mode can be realized in high-confinement waveguides (such as photonic crystal fibers), but achieving the anomalous waveguide dispersion necessary for phase matching at pump wavelengths near ∼1 μm (where the highest power fiber lasers emit) comes at the cost of reducing the effective area of the mode, thus limiting power-handling. Here, we specifically consider the class of Bessel-like LP0,m modes in step-index fibers. It has been shown that these modes can be selectively excited and guided stably for long lengths of fiber, and mode stability increases with mode order ‘m’. The effective area of modes in these fibers can be very large (>6000 μm2 demonstrated) and is decoupled from dispersion, allowing for phase matching within a single mode in a power-scalable platform. Furthermore, step-index fibers can guide many different LP0,m modes, allowing access to a highly multi-moded basis set with which to study FWM interactions between different modes. In this thesis we develop techniques to excite, propagate, and characterize LP0,m modes in order to demonstrate FWM in two regimes: monomode interactions comprising waves all belonging to the same mode, and intermodal interactions between different modes. In the monomode regime we demonstrate parametric sources which operate at near-infrared wavelengths under-served by conventional fiber lasers, including 880, 974, 1173, and 1347 nm. The output pulses for these systems are ∼300 ps in duration and reach peak powers of ∼10 kW, representing, to the best our knowledge, the highest peak power fiber laser sources demonstrated at these wavelengths to date. In the intermodal regime, we demonstrate a cascade of FWM processes between different modes that lead to a series of discrete peaks in the visible portion of the spectrum, increasing monotonically in mode order from LP0,7 at 678 nm to LP0,16 at 443 nm. This cascade underscores the huge number of potential FWM interactions between different LP0,m modes available in a highly multi-mode fiber, which scale as N4 for N guided modes. Finally, we demonstrate a novel intermodal FWM process pumped between the LP0,4 and LP0,5 modes of a step-index fiber, which provides broadband FWM gain (63 nm at 1550 nm) while maintaining wavelength separations of nearly an octave (762 nm) – a result that cannot be replicated in the single-mode regime. We seed this process to generate a ∼10 kW, ∼300-ps pulsed fiber laser wavelength-tunable from 786-795 nm; representing a fiber analogue of the ubiquitous Ti:Sapphire laser.

This thesis presents several advances in the technology and applications of photonic crystal fibres achieved over the last three years. Chapters 1 and 2 give the background material important to understand the results presented in chapters 3, 4 and 5. In chapter 1, linear properties of optical fibres are described. This chapter focuses particularly on how the engineering of the cladding structure of solid core photonic crystal fibres can be used to vary the fibre properties, most importantly the group index and dispersion. Propagation in all-solid photonic bandgap fibres is also discussed in terms of the anti-resonant reflecting optical waveguide model. Chapter 2 introduces the nonlinear optical effects that are important to understand the work presented in chapters 4 and 5. In chapter 3, a method to reduce bend losses in all-solid photonic bandgap fibres is outlined. The reduction of these losses is achieved by redesigning the high-index inclusions in the cladding structure to suppress cladding modes that strongly couple to the fundamental core-guided mode when the fibre is bent. In chapter 4, a method of tapering photonic crystal fibres in order to decrease the dispersion along their length is described. The tapers are used to compress solitons via adiabatic soliton compression and a combination of adiabatic soliton compression and soliton effect compression, achieving a factor of 15 compression of a transform-limited pulse to below 50 fs. Chapter 5 describes how engineering the cladding structure of photonic crystal fibres can be used to generate shorter frequencies in supercontinuum generation. The method by which this achieved is experimentally verified and then exploited to generate a continuum incorporating the entire visible spectrum using low cost, low maintenance pump sources.

Hui Yuen Yung. / Thesis submitted in: August 1998. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1999. / Includes bibliographical references (leaves 70-73). / Text in English; abstract also in Chinese. / Hui Yuen Yung. / Acknowledgements --- p.vi / Abstract --- p.vii / Chapter 1 --- Introduction --- p.1 / Chapter 2 --- Second harmonic generation --- p.5 / Chapter 2.1 --- Introduction --- p.5 / Chapter 2.2 --- Maxwell's equations in dielectric media --- p.6 / Chapter 2.3 --- Second harmonic generation --- p.7 / Chapter 2.4 --- Phase matching --- p.8 / Chapter 2.5 --- Quasi phase matching --- p.10 / Chapter 2.6 --- Inversion symmetry --- p.11 / Chapter 3 --- Third order nonlinear optical processes in optical fibers --- p.14 / Chapter 3.1 --- Introduction --- p.14 / Chapter 3.2 --- Optical fibers --- p.15 / Chapter 3.3 --- Third order interaction between waves of same frequency --- p.16 / Chapter 3.4 --- Third order interaction between waves of different frequencies --- p.19 / Chapter 4 --- Multiphoton ionization interference effect --- p.23 / Chapter 4.1 --- Historical development --- p.23 / Chapter 4.2 --- Multiphoton ionization interference effect --- p.26 / Chapter 4.3 --- Periodic ionization --- p.27 / Chapter 4.4 --- Periodic electric field --- p.28 / Chapter 4.5 --- Physical interpretation --- p.29 / Chapter 5 --- Experimental setup --- p.32 / Chapter 5.1 --- Introduction --- p.32 / Chapter 5.2 --- Laser system --- p.32 / Chapter 5.3 --- Optical fibers --- p.33 / Chapter 5.4 --- Coupling light into fibers --- p.34 / Chapter 5.5 --- Detection system --- p.36 / Chapter 5.6 --- Optical layout --- p.36 / Chapter 6 --- Second harmonic generation in optical fibers --- p.40 / Chapter 6.1 --- Introduction --- p.40 / Chapter 6.2 --- Self-preparation in optical fibers --- p.41 / Chapter 6.3 --- Polarization dependence --- p.42 / Chapter 6.4 --- Seeding optical fibers --- p.42 / Chapter 6.5 --- Seeding by varying green light intensity --- p.45 / Chapter 6.6 --- Square dependence of second harmonic generation in optical fibers --- p.46 / Chapter 7 --- Erasure of x(2) grating in optical fibers --- p.56 / Chapter 7.1 --- Introduction --- p.56 / Chapter 7.2 --- Experiment --- p.58 / Chapter 7.3 --- Results --- p.59 / Chapter 7.3.1 --- Erasure by different propagating mode --- p.59 / Chapter 7.3.2 --- Erasure in germanium-doped fiber --- p.60 / Chapter 7.3.3 --- Erasure in erbium-doped fiber --- p.61 / Chapter 7.4 --- Discussion --- p.61 / Chapter 8 --- Conclusion --- p.68 / Chapter 8.1 --- Summary of our work --- p.68 / Chapter 8.2 --- Outlook --- p.69 / Chapter 8.2.1 --- Multiphoton ionization in polymer --- p.69 / Chapter 8.2.2 --- Erasure by blue light --- p.69 / Bibliography --- p.70

Song Liang = 向列液晶中激光束感应的取向重联非线性光学效应和取向性光折变光栅形成 / 宋亮. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2006. / Includes bibliographical references. / Text in English; abstracts in English and Chinese. / Song Liang = Xiang lie ye jing zhong ji guang shu gan ying de qu xiang zhong lian fei xian xing guang xue xiao ying he qu xiang xing guang zhe bian guang zha xing cheng / Song Liang. / Abstract --- p.i / 论文摘要 --- p.iii / Acknowledgement --- p.iv / Contents --- p.v / Chapter Chapter 1 --- Introduction --- p.1 / References --- p.5 / Chapter Chapter 2 --- Brief review of liquid crystals and nonlinear optics of liquid crystals --- p.9 / Chapter 2.1 --- Brief review of liquid crystals --- p.9 / Chapter 2.1.1 --- General description --- p.9 / Chapter 2.1.2 --- Types of liquid crystals --- p.11 / Chapter 2.1.3 --- Order parameter --- p.14 / Chapter 2.1.4 --- Liquid crystal alignment --- p.14 / Chapter 2.1.5 --- Continuum theory of liquid crystals --- p.16 / Chapter 2.2 --- Nonlinear optics of liquid crystals --- p.20 / Chapter 2.2.1 --- Basic mechanism of nonlinear optics --- p.20 / Chapter 2.2.2 --- Self-phase modulation --- p.23 / Chapter 2.2.3 --- Orientational photorefractive effects --- p.29 / Chapter 2.3 --- Sample preparation --- p.34 / Chapter 2.4 --- Conclusion --- p.37 / References --- p.39 / Chapter Chapter 3 --- Domain formation in homeotropic nematic liquid crystal cell --- p.42 / Chapter 3.1 --- Introduction --- p.42 / Chapter 3.2 --- Domain formation under applied dc and ac electric fields --- p.44 / Chapter 3.3 --- Light scattering of domains under applied dc and ac electric fields --- p.49 / Chapter 3.4 --- Conclusion --- p.53 / References --- p.54 / Chapter Chapter 4 --- Laser induced self-phase modulation and effects of applied electric field --- p.56 / Chapter 4.1 --- Introduction --- p.56 / Chapter 4.2 --- Self-phase modulation without applied electric field --- p.58 / Chapter 4.2.1 --- Experimental setup --- p.58 / Chapter 4.2.2 --- Experimental results and discussions --- p.59 / Chapter 4.3 --- Effects of applied electric field --- p.67 / Chapter 4.3.1 --- Effects of applied dc electric field --- p.67 / Chapter 4.3.2 --- Effects of applied ac electric field --- p.72 / Chapter 4.4 --- Conclusion --- p.75 / References --- p.77 / Chapter Chapter 5 --- Orientational photorefractive grating in nematic liquid crystals --- p.80 / Chapter 5.1 --- Introduction --- p.80 / Chapter 5.2 --- Orientational photorefractive grating under dc electric field --- p.82 / Chapter 5.2.1 --- Experimental setup --- p.82 / Chapter 5.2.2 --- Experimental results and discussion --- p.84 / Chapter 5.3 --- Orientational photorefractive grating under ac electric field --- p.90 / Chapter 5.3.1 --- Raman-Nath grating --- p.90 / Chapter 5.3.2 --- Quasi-Bragg grating --- p.96 / Chapter 5.4 --- Conclusion --- p.98 / References --- p.100 / Chapter Chapter 6 --- Summary and future outlook --- p.103 / List of Publications and Conference Presentations --- p.107

Lee Sim Heung. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2005. / Includes bibliographical references. / Abstracts in English and Chinese. / ABSTRACT --- p.i / ACKNOWLEGEMENT --- p.vi / LIST OF FIGURES --- p.xi / Chapter 1. --- INTRODUCTION --- p.1 / Chapter 1.1. --- New challenges in telecommunication --- p.2 / Chapter 1.2. --- Introduction to optical non-linearity and its impact to optical network --- p.3 / Chapter 1.3. --- Applications of optical nonlinearity --- p.5 / Chapter 1.3.1. --- Extinction ratio enhancement and wavelength conversion --- p.5 / Chapter 1.3.2. --- All optical ASK to DPSK converter --- p.6 / Chapter 1.3.3. --- All-optical RZ to NRZ format converter --- p.8 / Chapter 1.3.4. --- RF clock component enhancement for NRZ data --- p.10 / Chapter 1.3.5. --- Multi-wavelength converter with multi-channel broadcasting --- p.11 / Chapter 1.4. --- Overview --- p.12 / Chapter 2. --- PRINCIPLES AND THEORIES --- p.18 / Chapter 2.1. --- Optical nonlinearity --- p.19 / Chapter 2.2. --- Self-phase modulation (SPM) --- p.21 / Chapter 2.3. --- Cross-phase modulation (XPM) --- p.25 / Reference: --- p.28 / Chapter 3. --- EXTINCTION RATIO ENHANCEMENT AND WAVELENGTH CONVERSION USING CROSS-PHASE MODULATION IN A DISPERSION-SHIFTED FIBER --- p.29 / Chapter 3.1. --- Introduction --- p.30 / Chapter 3.2. --- Experimental details of extinction ratio enhancement --- p.31 / Chapter 3.3. --- Result and Discussions --- p.32 / Chapter 3.4. --- Conclusion --- p.36 / References: --- p.37 / Chapter 4. --- ALL-OPTICAL ASK TO DPSK FORMAT CONVERSION --- p.38 / Chapter 4.1. --- All Optical ASK to DPSK Format Conversion Using Cross-Phase Modulation in a Non-linear Fiber --- p.39 / Chapter 4.1.1. --- Introduction --- p.40 / Chapter 4.1.2. --- Experimental Details of ASK to DPSK format conversion by XPM in DSF --- p.42 / Chapter 4.1.3. --- Results and Discussion --- p.44 / Chapter 4.1.4. --- Experimental Details of ASK to DPSK format conversion by XPM in PCF --- p.47 / Chapter 4.1.5. --- Result and Discussion of XPM in PCF --- p.49 / Chapter 4.1.6. --- Comparison of DSF and PCF --- p.51 / References: --- p.54 / Chapter 4.2. --- All Optical ASK to ASK/DPSK Orthogonal Code Format Conversion Using Cross-Phase Modulation in a Dispersion-Shifted Fiber --- p.56 / Chapter 4.2.1. --- Introduction --- p.57 / Chapter 4.2.2. --- Experimental Details of ASK to ASK/DPSK format conversion --- p.58 / Chapter 4.2.3. --- Results and Discussion --- p.60 / Chapter 4.2.4. --- Conclusion --- p.63 / References: --- p.64 / Chapter 5. --- ALL-OPTICAL RZ TO NRZ FORMAT CONVERSION --- p.65 / Chapter 5.1. --- Introduction --- p.65 / Chapter 5.2. --- All-Optical RZ to NRZ Data Format Conversion Using Spectral Broadening Effect in a Dispersion-Shifted Fiber --- p.67 / Chapter 5.2.1. --- Principle of RZ-to-NRZ format conversion using SPM --- p.68 / Chapter 5.2.2. --- Experiment Details --- p.71 / Chapter 5.2.3. --- Results and Discussion --- p.72 / Chapter 5.2.4. --- Conclusion --- p.77 / Chapter 5.3. --- Spectral Filtering from a Cross-Phase Modulated Signal for RZ to NRZ Format and Wavelength Conversion --- p.78 / Chapter 5.3.1. --- Principle of RZ to NRZ format conversion by XPM --- p.79 / Chapter 5.3.2. --- Experiment --- p.81 / Chapter 5.3.3. --- Results and Discussion --- p.83 / Chapter 5.3.4. --- Conclusions --- p.87 / References: --- p.88 / Chapter 6. --- ALL-OPTICAL CLOCK COMPONENT EXTRACTION FROM NRZ DATA SIGNALS USING SELF-PHASE MODULATION IN A DISPERSION-SHIFTED FIBER --- p.90 / Chapter 6.1. --- Introduction --- p.91 / Chapter 6.2. --- Experimental Details --- p.92 / Chapter 6.3. --- Results and Discussion --- p.93 / Chapter 6.4. --- Conclusion --- p.96 / References: --- p.97 / Chapter 7. --- ALL-OPTICAL WAVELENGTH MULTICASTING USING SELF- PHASE MODULATION IN A NONLINEAR PHOTONIC CRYSTAL FIBER --- p.98 / Chapter 7.1. --- Introduction --- p.99 / Chapter 7.2. --- Simulation results --- p.100 / Chapter 7.3. --- Experimental Details --- p.103 / Chapter 7.4. --- Result and Discussion --- p.104 / Chapter 7.5. --- Conclusions --- p.109 / References: --- p.110 / Chapter 8. --- CONCLUSION AND FUTURE WORK --- p.111 / Chapter 8.1. --- Conclusion --- p.111 / Chapter 8.2. --- Possible Future Work --- p.114 / References: --- p.116 / APPENDIX --- p.117 / List of Publications --- p.117

This thesis investigates two thematic lines of research, both underpinned by non-Markovian system-reservoir interactions in quantum optics. The overarching focus is on modelling the open system dynamics in a non-perturbative fashion, broadly on - though not restricted to - instances when the environment is structured. A theory is developed by means of enlarging the open system over environmental degrees of freedom to include memory effects in its dynamics. This is achieved using an established technique that involves mapping a bosonic environment onto a 1D chain of harmonic oscillators. Within this setting, we apply a Heisenberg equation-of-motion approach to derive an exact set coupled differential equations for the open system and a single auxiliary oscillator of the chain. The combined equations are shown to have their interpretation rooted in a quantum Markov stochastic process. Including the auxiliary chain oscillator as part of the original system then enables us to obtain an exact master equation for the enlarged system, avoiding any need for the Born-Markov approximations. Our method is valid for a dissipative two-state system, with cases of multiple excitations and added driving discussed. Separately, we apply the framework of quantum Darwinism to an atom-cavity system, and, subsequently, to a more general multiple-environment model. In both cases, the time-dependent spread of correlations between the open system and fractions of the environment is analysed during the course of the decoherence process. The degree to which information is redundant across different fractions is checked to infer the emergence of classicality. In the second case, we go further and present a decomposition of information in terms of its quantum and classical correlations. A quantitative measure of redundancy is also studied with regard to its ability to witness non-Markovian behaviour. Besides fundamental interest, our results have application to quantum information processing and quantum technologies, keeping in mind the potential beneficial use of non-Markovian effects in reservoir engineering.

The objective of this thesis is to develop the quantum theory of the motional degrees of freedom of a charged particle in a Penning trap. The theory is treated within the formalism of quantum optics, and explores the use of dressed-atom methods by exploiting the threefold SU(N) algebraic structure of the problem. The quantum form of the experimental techniques of sideband coupling and driving to the ultra-elliptical regime are examined in this context, and resulting future applications considered. Interpretation of the quantum dynamics of the separate x and y motions of an electron is discussed, motivated by the desire to modify the trapping potential without changing the basic experimental configuration. A detailed discussion of operator methods which exploit the algebraic structure of the problem is given. This results in a clearer understanding of the physical manifestations of a range of unitary transformations upon a general three-dimensional system, and a novel interpretation of the mapping between canonical angular momentum components of isotropic and anisotropic trapping systems. The results highly promote future use of these methods in Penning trap theory, detailing a robust formulation of unitary operations which can be used to prepare the quantum state of a charged particle. The majority of the results can be applied to any Penning trap, but the theory is based throughout upon the “Geonium Chip" trap at Sussex; the scalability and planar design of this trap promotes it as natural candidate in experimental quantum optics and Gaussian quantum information studies. The work in this thesis aims to provide framework for such future applications.