Light-matter interactions are essential for the development of many modern technologies and for fundamental science. Hence, many recent efforts have focused on understanding light-matter interaction in exotic classes of materials, particularly in subwavelength (nanometre scale) regimes. This Master's thesis focuses on two different types of materials whose interaction length is typically in the nanoscale. First, we studied and observed the energy transfer between two ultrashort beam pulses in the epsilon-near-zero (ENZ) spectral range of a material, classified where the real part of the material's electric permittivity has a magnitude much less than 1. Typically, such energy transfer in ordinary materials (such as fused silica) requires different wavelengths of both beams interacting in the material. However, ENZ materials have an unprecedentedly high optical nonlinearity, leading to self-manifesting energy transfer. This self-manifesting effect occurs in ENZ material due to the effective frequency shift known as adiabatic frequency conversion (AFC) caused by a significant change of refractive index from its large optical nonlinearity. Second, we studied a class of materials known as metasurfaces, which are built from an array of artificial engineered nano-antennas. Metasurfaces can enable custom wavefront control or the engineering of coupling to designated surface modes, which is not possible for naturally occurring optical surfaces. In this thesis, we developed a design scheme for constructing a metasurface that generates multiple lattice resonances at desired wavelengths. Such a design scheme is possible because we arranged the nano-antennas using Fourier analysis. This flexible scheme produces a metasurface design directly from the desired distribution of resonances.

Light manipulation is an important method to enhance the light-matter interactions in micro and nano photonic materials and structures by generating usefulelectric field components and increasing time and pathways of light propagationthrough the micro and nano materials and structures. For example, quantum wellinfrared photodetector (QWIP) cannot absorb normal incident radiation so thatthe generation of an electric field component which is parallel to the original incident direction is a necessity for the function of QWIP. Furthermore, the increaseof time and pathways of light propagation in the light-absorbing quantum wellregion will increase the chance of absorbing the photons.The thesis presents the theoretical studies of light manipulation and light-matter interaction in micro and nano photonic materials and structures, aiming atimproving the performance of optical communication devices, photonic integrateddevices and photovoltaic devices.To design efficient micro and nano photonic devices, it is essential to knowthe time evolution of the electromagnetic (EM) field. Two-dimensional and three-dimensional finite-difference time-domain (FDTD) methods have been adopted inthe thesis to numerically solve the Maxwell equations in micro and nano photonicmaterials and structures.Light manipulation in micro and nano material and structures studied in thisthesis includes: (1) light transport in the photonic crystal (PhC) waveguide, (2)light diffraction by the micro-scale dielectric PhC and metallic PhC structures(gratings); and (3) exciton-polaritons of semiconductor quantum dots, (4) surfaceplasmon polaritons at semiconductor-metallic material interface for subwavelengthlight control. All these aspects are found to be useful in optical devices of multiplebeam splitter, quantum well/dot infrared photodetectors, and solar cells. / QC 20120507

Chaos is a complex dynamics with exponential sensitivity to the initial conditions. Since the study of three-body problem by Henri Poincare, chaos has been extensively studied in many systems, ranging from electronics to fluids, brains and more recently photonics. Chaos is a ubiquitous phenomenon in Nature, from the gigantic oceanic waves to the disordered scales of white beetles at nanoscale. The presence of chaos is often unwanted in applications, as it introduces unpredictability,which makes it difficult to predict or explain experimental results. Inspired by how chaos permeates the natural world, this thesis investigates on how the interaction between light and chaotic structure can enhance the performance of photonics devices. With a proper design of the lighter-mater interaction in chaotic resonators, I illustrate how chaos can be used to enhance the ability of an optical cavity to store electromagnetic energy, realize a blackbody system composed of gold nanoparticles, localize light beyond the diffraction limit and control the phase transition of super-radiance.

Doctor of Philosophy / Department of Industrial & Manufacturing Systems Engineering / Shuting Lei / Lasers have been widely used as a manufacturing tool for material processing, such as drilling, cutting, welding and surface texturing. Compared to traditional manufacturing methods, laser-based material processing is high precision, can treat a wide range of materials, and has no tool wear. However, demanding manufacturing processes emerging from the needs of nano and 3D fabrication require the development of laser processing strategies that can address critical issues such as machining resolution, processing speed and product quality. This dissertation concerns the development of novel laser processing strategies based on spatial, temporal and spectral control of light-matter interaction. In the spatial domain, beam shaping is employed in ultrafast laser micro-processing. Zero-order Bessel beam, generated by an axicon, is used for selective removal of the back contact layer of thin film solar cells. Bessel beam’s propagation-invariance property gives rise to an extension of focal range by orders of magnitude compared to Gaussian beam, greatly increasing process tolerance to surface unevenness and positioning error. Together with the axicon, a spatial light modulator is subsequently used to modify the phase of laser beam and generate superpositions of high-order Bessel beam with high energy efficiency. With the superposed beam, processing speed can be increased significantly, and collateral damage resulting from the ring structures in the zero-order Bessel beam can be greatly suppressed. In the temporal domain, it is demonstrated that ionization in dielectric materials can be controlled with a pair of ultraviolet and infrared pulses. With the assistance of the long-wavelength infrared pulse, nano-scale features are achieved using only a small fraction of threshold energy for the short-wavelength pulse. Computer simulation based on the rate equation model is conducted and found to be in good agreement with experimental results. This study paves the way for future adoption of short-wavelength laser sources, for example in the extreme ultraviolet range, for direct laser nano-fabrication with below-threshold pulse energy. In the spectral domain, a short-wavelength infrared laser is used to generate modification in the bulk of silicon wafers, in an attempt to develop 3D fabrication capabilities in semiconductors. Issues such as spherical aberration correction and examination procedure are addressed. Permanent modification is generated inside silicon by tightly focusing and continuously scanning the laser beam inside the samples, without introducing surface damage. The effect of laser pulse energy and polarization is also investigated. These results demonstrate the potential of controlling laser processing in multiple dimensions for manufacturing purposes, and point to a future when laser can be used as naturally and efficiently as mechanical tools used today, but is targeted at more challenging problems.

An important aspect of third-order optical nonlinearity is the intensity-dependent refractive index, where the intensity of the light itself affects the refractive index. This nonlinear effect is known as Kerr nonlinearity. In this work, a theory of amplification based on Kerr nonlinearity is developed. Kerr nonlinearity is well known to exhibit instability. Our amplification theory is based on seeding this instability. The full theory is developed to obtain the vectorial wave equations of the instability. It is shown that for materials of interest, vectorial effects are negligible across the instability regime and the scalar theory gives an accurate account of Kerr instability amplification. It is also shown that this instability analysis is a spatiotemporal generalization to four-wave mixing, modulation instability, and filamentation instability. It fact, it can be considered a seeded conical emission process. Subsequently, the theory of plane wave Kerr instability is explored. Quantitatively, the importance of pump wavelength, linear dispersive properties, and non-collinear angles for optimal amplification are demonstrated. Next, the seed beam is generalized to a finite Gaussian pulse in both time and space; the effect of a finite seed beam is quantitatively analyzed. Our analysis of Kerr instability in bulk dielectric crystals demonstrates the potential to amplify pulses in the wavelength range of ~1-14 μm. Whereas plane wave amplification is shown to extend to 40 μm in the example materials shown, material damage limits finite pulse Kerr instability amplification to about 14μm. There, seed pulse output energies in the 50 μJ range appear feasible with a ratio of pump to seed pulse energy in the range 400-500. Three key aspects of Kerr amplification are the capacity for single cycle pulse amplification, that it is intrinsically phase-matched, and its simplicity and versatility. As the Kerr instability gain profile is of Bessel-Gaussian nature in the transverse space domain, it lends itself naturally to the amplification of Bessel-Gauss beams. It is shown that pump-to-seed energy amplification that is more effcient than the Gaussian case by a factor of about 5-7. Whereas in the Gaussian case, the efficiency is on the order of about 0.15-0.2%, in the Bessel-Gaussian case it is on the order of about 1%. It is also demonstrated that Bessel-Gaussian seed beams centered at longer wavelengths than ordinary Gaussian beams may be amplified. Lastly, Bessel-Gauss beams are known to have favourable properties, such as being diffraction-free over a certain propagation range. Finally, a quantum optical theory of Kerr instability is developed. In particular, we explore a theory of the generation of ultrashort photon pairs (biphotons) from vacuum with Kerr instability.

The nanoscale manipulation of soft-matter, such as biological tissues, in its native environment has promising applications in medicine to correct for defects (eg. eye cataracts) or to destroy malignant regions (eg. cancerous tumours). To achieve this we need the ability to first image and then do precise ablation with sub-micron resolution with the same setup. For this purpose, we designed and built a multiphoton microscope and tested it on goldfish gills and bovine cells. We then studied light-matter interaction on a hard polymer (PMMA) because the nature of ablation of soft-matter in its native environment is complex and not well understood. Ablation and modification thresholds for successive laser shots were obtained. The ablation craters revealed 3D nanostructures and polarization dependent orientation. The interaction also induced localized porosity in PMMA that can be controlled.

The nanoscale manipulation of soft-matter, such as biological tissues, in its native environment has promising applications in medicine to correct for defects (eg. eye cataracts) or to destroy malignant regions (eg. cancerous tumours). To achieve this we need the ability to first image and then do precise ablation with sub-micron resolution with the same setup. For this purpose, we designed and built a multiphoton microscope and tested it on goldfish gills and bovine cells. We then studied light-matter interaction on a hard polymer (PMMA) because the nature of ablation of soft-matter in its native environment is complex and not well understood. Ablation and modification thresholds for successive laser shots were obtained. The ablation craters revealed 3D nanostructures and polarization dependent orientation. The interaction also induced localized porosity in PMMA that can be controlled.

The nanoscale manipulation of soft-matter, such as biological tissues, in its native environment has promising applications in medicine to correct for defects (eg. eye cataracts) or to destroy malignant regions (eg. cancerous tumours). To achieve this we need the ability to first image and then do precise ablation with sub-micron resolution with the same setup. For this purpose, we designed and built a multiphoton microscope and tested it on goldfish gills and bovine cells. We then studied light-matter interaction on a hard polymer (PMMA) because the nature of ablation of soft-matter in its native environment is complex and not well understood. Ablation and modification thresholds for successive laser shots were obtained. The ablation craters revealed 3D nanostructures and polarization dependent orientation. The interaction also induced localized porosity in PMMA that can be controlled.

The nanoscale manipulation of soft-matter, such as biological tissues, in its native environment has promising applications in medicine to correct for defects (eg. eye cataracts) or to destroy malignant regions (eg. cancerous tumours). To achieve this we need the ability to first image and then do precise ablation with sub-micron resolution with the same setup. For this purpose, we designed and built a multiphoton microscope and tested it on goldfish gills and bovine cells. We then studied light-matter interaction on a hard polymer (PMMA) because the nature of ablation of soft-matter in its native environment is complex and not well understood. Ablation and modification thresholds for successive laser shots were obtained. The ablation craters revealed 3D nanostructures and polarization dependent orientation. The interaction also induced localized porosity in PMMA that can be controlled.

The constantly increasing volume of information in modern society demands a better understanding of the physics and modeling of optical phenomena, and in particular, optical waveguides which are the central component of information systems. Two ways of advancing this physics are to push current technologies into new regimes of operation, and to study novel materials which offer superior properties for practical applications. This dissertation considers two problems, each addressing the above-mentioned demands. The first relates to the influence of high-order nonlinear effects on pulse collisions in existing high-speed communication systems. The second part is a study of pulse dynamics in a novel nanocomposite medium which offers great potential for both optical waveguide physics and applications. The nanocomposite consists of metallic nanoparticles embedded in a host medium. Under resonance conditions, the optical field excites plasmonic oscillations in the nanoparticles, which induce a strong nonlinear response.Analytical and computational tools are used to study these problems. In the first case, a double perturbation method, in which the small parameters are the reciprocal of the relative frequency of the colliding solitons and the coefficient of quintic nonlinearity, reveals that the leading order effects on collisions are radiation emission and phase shift of the colliding solitons. The analytical results are shown to agree with numerics. For the case of pulse dynamics in nanocomposite waveguides, the resonant interaction of the optical field and material excitation is studied in a slowly-varying envelope approximation, resulting in a system of partial differential equations. A family of solitary wave solutions representing the phenomenon of self-induced transparency are derived. Stability analysis reveals the solitary waves are conditionally stable, depending on the sign of the perturbation parameter. A characterization of two-pulse interaction indicates high sensitivity to relative phase, and collision dynamics vary from highly elastic to the extreme case where one wave is immediately destroyed by the collision, depositing its energy into a localized hotspot of material excitation. This last scenario represents a novel mechanism for "stopping light".