The recent emergence of super-resolution microscopy imaging techniques has surpassed the diffraction limit to improve image resolution. Contrary to the breakthroughs of spatial resolution, high temporal resolution remains a challenge. This dissertation demonstrates a simple, on axis, 4D (3D + time) multi-colour microscopy imaging (MCMI) technology that delivers simultaneous 3D broadband imaging over cellular volumes, which is especially applicable to the real-time imaging of fast moving biospecimens. Quadratically distorted (QD) grating, in the form of an off axis-Fresnel zone plate, images multiple object planes simultaneously on a single image plane. A delicate mathematical model of 2D QD grating has been established and implemented in the design and optimization of QD grating. Grism, a blazed grating and prism combination, achieves chromatic control in the 4D multi-plane imaging. A pair of grisms, whose separation can be varied, provide a collimated beam with a tuneable chromatic shear from a collimated polychromatic input. The optical system based on QD grating and grisms has been simply appended to the camera port of a commercial microscope, and a few bioimaging tests have been performed, i.e. the 4D chromatically corrected imaging of fluorescence microspheres, MCF-7 and HeLa cells. Further investigation of bioimaging problems is still in progress.

This thesis presents the results of an experimental study into the nonlinear optical properties of novel nonlinear materials at infrared regions of the electromagnetic spectrum for the realisation of nonlinear optical devices in the near- and mid-infrared. Because of its exceptional nonlinear optical properties and its promise of implementation in a range of mid-infrared applications graphene had a prominent place in this research. Extensive investigations in the nonlinear optical properties of single and multilayer chemical vapour deposition (CVD) graphene are presented. This study revealed that graphene presents a nonlinear phase shift due to a negative, irradiance-dependent nonlinear refraction. The high peak powers available enabled the study of both saturable absorption (SA) and two-photon absorption (2PA), identifying the irradiance limits at which the contribution of two-photon absorption exceeded that of saturable absorption. Moreover, the nonlinear optical properties of graphene-polyvinyl alcohol (G-PVA) composite films were studied. The results indicate the thermal damage of the host polymer due to graphene heating and temperature transfer. Studies in the third order nonlinear optical properties of chalcogenide glasses with the perspective of integration with graphene for the development of mid-infrared devices and applications are also performed. Of all the glasses investigated, gallium lanthanum sulphide (GLS) was found to have the most interesting nonlinear optical properties. Its optical Kerr nonlinearity was found to be approximately 35 times higher than silica and the upper limit of its two-photon absorption coefficient was the lowest of all the chalcogenide glasses analysed, implying that GLS would be an excellent candidate for ultrafast all-optical switching. Subsequently GLS was chosen as the host material for optical waveguide and device fabrication via ultrafast laser inscription (ULI). Near- and mid-infrared waveguides were successfully fabricated; fundamental features such as, refractive index profiles and material dispersion were investigated. The Zero Dispersion Wavelength (ZDW) of GLS was experimentally measured for the first time; the ZDW was determined to be between 3.66-3.71 μm for the waveguides and about 3.61 μm for the bulk. Single mode directional couplers at 1550 nm were also developed and their ultrafast all-optical switching properties were investigated, leading to the assessment of the nonlinear refractive index n2 of the ULI modified area. Furthermore, waveguides in Er3+ doped GLS were successfully fabricated and the infrared transitions at 1550 and 2750 nm were detected opening the potential for GLS waveguide lasers.

The propagation of light waves across a periodic array of evanescently coupled optical waveguides can be described by a Schr¨odinger-like equation for a particle in a periodic potential. This mapping allows us to investigate the dynamics of electrons in a crystalline solid using an artificial crystal of optical waveguides, known as a photonic lattice. The unique capabilities of ultrafast laser inscription enable us to design, fabricate and precisely control various properties of a photonic lattice. Here, we focus on the experimental construction of the Hamiltonians associated with various complex quantum systems using engineered photonic lattices, and then measure the time evolution of a given input state. In this photonic platform, we experimentally observe various single particle effects known from solid-state physics, such as the localised states associated with flat-band lattice geometries, localised Wannier-Stark states, photon-assisted tunnelling and the anomalous topological edge modes in slowly-driven lattices. Specific phenomena associated with particle interactions, such as the dynamics of two interacting particles in a one-dimensional lattice with static and sinusoidally driven Hubbard Hamiltonian, is also investigated. The experimental results presented here will be of interest to a large community, including physicists working on photonics, quantum optics, cold atomic gases, and condensed-matter physics.

This thesis addresses the development of broadly tunable, high repetition rate frequency combs in the mid-IR region. A novel PPKTP crystal design was used to provide phasematching for parametric oscillation and simultaneously give efficient pump+idler sum-frequency generation (SFG). This innovation enabled a fully stabilized idler comb from a 333-MHz femtosecond optical parametric oscillator to be generated in which the carrier envelope offset frequency fCEO together with the repetition frequency fREP were stabilised. This OPO platform was then extended to demonstrate, via harmonic pumping, a fully stabilized 1-GHz OPO frequency comb from a 333-MHz pump laser. Next, an alternative route to a 1-GHz OPO comb was investigated by synchronously pumping an OPO directly with a 1-GHz Ti:sapphire laser. Here the comb was fully stabilized for the signal, idler and pump pulses by using a narrow linewidth CW diode laser developed for the project and whose design is also presented. A further increase in the comb mode spacing was performed with a Fabry-Pérot cavity. A stabilised cavity was used to filter 1.5 m signal pulses from a 333-MHz repetition rate OPO frequency comb to yield a 10-GHz comb. The length of the Fabry-Pérot cavity was dither locked to a single-frequency ECDL and later on directly to the OPO frequency comb. Finally the 333-MHz OPO comb was demonstrated in an optical frequency metrology experiment. The frequency comb mode number and the absolute frequency of a narrow-linewidth CW laser were measured and the performance of the OPO comb was found to be comparable to that of a commercial fibre laser comb used as a benchmark in the experiment.

The use of laser surface texturing (LST) for surface engineering, in particular the generation of high static friction surfaces, has been investigated. The niche nature of high friction surfaces has meant that the field has largely been discarded and forgotten, leaving an opening for novel and innovative research as a result. Several regimes for generating high friction surfaces were considered: exclusive use of LST on a single surface (as in a shim configuration), use of LST on both surfaces of a contact and LST of a single surface in conjunction with additional surface engineering processes. Each of these three regimes was found to operate by a different mechanism of high friction, namely adhesion, interlocking and embedding. The laser surface texturing was performed using a self-built, commercially available laser processing workstation encompassing a pulsed nanosecond fibre laser and galvanometric scanner. Analysis of the surface textures was performed using optical microscopy and profilometry with further investigations performed by cross-section, SEM and EDX analysis. Friction testing of the textured samples was performed by a custom made testing rig, with direct measurement of the applied normal force via an in-line load cell, and real-time measurement of the load force by a 100kN hydraulic press. A wide range of laser texturing parameters and material properties were investigated, with each of the three regimes exhibiting different optimal parameters. High friction coefficients (μs > 0.8) can be repeatedly obtained at normal pressures of up to 100MPa when LST has been used in conjunction with additional surface engineering (hardening) processes and when both surfaces of the contact have been treated with laser surface texturing. In the latter case, static friction coefficients of μs~1 with processing rates of greater than 1cm2/s have been achieved. Several relevant applications for such high friction surfaces have also been discussed. The feasibility of integrating beam shaping optics into an industrial style laser processing workstation has also been demonstrated and possible applications for such shaped beams discussed.

The work discussed in this thesis deals with the generation, control and modulation of optical interactions in two-dimensional materials, specifically in unpatterned, subwavelength graphene multilayers, using the process of Coherent Perfect Absorption (CPA). It aims to address the problem of inefficient light-matter coupling at the nanoscale by studying new geometries for enabling total absorption in 50% absorbing graphene films. Total optical absorption is demonstrated and a 80% modulation of the absorption and scattering is achieved by controlling the relative phases of the interacting optical beams. Degenerate four-wave mixing (DFWM) in graphene multilayers leads to the generation of optical phase conjugation and negative refraction. These nonlinear responses are generated with a conversion efficiency of 5 x 10-5, and using the CPA arrangement their amplitudes are modulated with a modulation contrast of 100%. It is shown that the two-dimensionality of graphene gives rise to a ‘phase-dependent’ nonlinearity, which differs significantly from that in bulk materials. The optical nonlinearity in graphene is seen to be controlled by the relative phases of the interacting optical fields in a manner such that the nonlinear polarisation itself can be switched on or off. The phase-dependent nonlinearity of the two-dimensional medium is then explored in three alternative geometries. The first one uses only two input beams, and a light-with-light modulation of the nonlinear signals is observed with a contrast of 90%. The second geometry involves a single beam interacting with the sample, wherein, nonlinear signals are generated in a self-pumping mode, due to reflection from a mirror placed very close to the graphene sample. The last configuration also uses a mirror in order to require only a single light beam and leads to the observation of a ‘negative reflection’ signal. Finally, a nonlinear imaging technique ‘phase-contrast imaging’ is performed using a traditional DFWM configuration with three input optical fields. A phase-object applied on one of the pump beams is transformed into an intensity object in the resulting negative refraction. A few basic phase objects are imaged on the negatively refracted beam and are reported in this work, offering a possible application for the advantages offered by two-dimensional optical nonlinearities.

Light-matter interaction, which is at the heart of the science and technology of light, can be controlled and designed in materials structured at the nanometre length-scale, for enhanced light emission and absorption, and down to the single photon level. The aim of this thesis is to investigate complex photonic geometries, i.e. systems where the collective interaction of a large number of constituents denes the optical properties with emergent phenomena beyond the sum of the response of the individual constituents. In particular, a central topic is the emission of light from sources located in dielectric and plasmonic networks with dierent degree of disorder and correlation. Experimental and theoretical evidence of coupling of single photons to propagating modes in nano-waveguides, emission enhancement in plasmonic structures, and collective emission in disordered lasing systems are presented. Large coupling of individual quantum dots embedded in free-standing sub-wavelength waveguides is experimentally demonstrated. These waveguides are fabricated by electrospinning, a scalable technique suitable for the realisation of large interconnected systems. Light emission enhancement is investigated in plasmonic self-assembled systems and lithographic structures, which build on the framework of optical antennas and allows isolating local and global contributions to the local density of states around a topological percolation phase transition. One of the most important cooperative eects between multiple emitters is lasing. Random lasing is investigated numerically and experimentally in diusive systems with particular attention to the spectral properties of the emission and its relation with the physical and chemical parameters of the surrounding environment, which can be exploit to tune the lasing emission, thus providing a novel sensing scheme. These results provide the building blocks to construct a photonic network of emitters coupled by simple optical links.

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This thesis presents a detailed research work on the fabrication, characterisation and applications of optical fibre grating devices with operation wavelengths cover from near- to mid- infrared (IR) range. One of the major contributions described in this thesis is the systematic investigation on the structures, fabrication methods and spectral, thermal, strain and surrounding refractive index (SRI) characteristics of near-IR fibre gratings including fibre Bragg gratings (FBGs), chirped fibre Bragg grating (CFBGs) and long period grating (LPGs). For some applications, such as special engineering sensors and high power fibre laser, the fibre gratings have been fabricated on different novel fibres (metal coated fibre and large mode field fibre), respectively. Another important contribution from the studies is experimental investigation on 45º tilted fibre gratings (45°-TFGs) and excessively tilted fibre gratings (ex-TFGs), and their applications. 45º-TFGs with high polarisation dependent loss (PDL) in single mode and polarisation maintaining (PM) fibres have been fabricated. The 45°-TFG has been employed as in fibre polariser to obtain the single polarised laser, which has been further developed as transverse loading sensor achieving high sensitivities. Furthermore, all fibre Lyot filter with narrow bandwidth (26 pm), constructed by two 45º-TFGs with 100m long cavity in PM fibre has been demonstrated. For ex-TFGs, SRI sensor based on a surface modified 81°-TFG, showing capability to detect glucose concentration with relatively high RI sensitivity (~168nm/RIU). Finally, an all-fibre loading sensor based on a hybrid 45° and 81° TFG structure has been demonstrated. Finally, I have fabricated fibre gratings into mid-IR 2μm range. The mid-IR FBGs have been evaluated for thermal and strain response, revealing higher temperature sensitivities than that in near-IR range. The mid-IR LPGs have been investigated for the thermal and refractive index sensitivities, also showing significant enhancement. The 45°-TFGs in mid-IR have been investigated for their PDL characteristics. The mid-IR FBGs and 45°-TFGs have been employed in Tm-doped fibre laser cavity to realize multi-wavelength continued wave (CW) and single polarisation operation.

No description available.