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The localisation of the interaction position of ? rays in scintillator detectors are of interest for different applications such as nuclear medicine, astronomy, fundamental physics experiments and nuclear security. For instance, the localisation of the interaction position of gamma rays in a detector can provide information about reconstructing the actual source position such as the one used in Compton cameras meant for nuclear security. The 3D scintillator detector described in this thesis consists of a 50.44×50.44×50.44 mm3 cubic CsI:Tl crystal coupled, for the first time, to six 8×8 SiPM arrays on all of the six faces of the crystal. 2D average and single light maps were generated to visualise the interaction positions. The measurements were also compared to Geant4 simulations and a simplistic geometrical model, and both showed a reasonable agreement with each other. The interaction position was successfully determined by using the light ratio method using both experimental and simulation data. Covering all of the six sides of the detector simplified the localisation and the 3D position reconstruction of the rays interaction inside the detector. All of the three coordinates were reconstructed using the ? 2 minimisation that uses the estimation based on the data of the simplistic model. The position resolution was measured at the edges and the central region of the detectors using the reconstructed data obtained from both these methods. At the edges, the resolution was found to be 1.4 mm and 2.6 mm, whereas in the central region, it was calculated to be 2.3 mm and 3.7 mm for the ? 2 minimisation and the light-sharing method respectively. The results obtained are exciting, and the interaction positions can be reconstructed using the light-sharing measurements obtained from all of the six arrays. Moreover, the position resolution can be quantified by using the reconstructed events light distribution.

Measurements on states of light underpins the entire fields of classical and quantum optics. Without measurement we are unable to gain any information about the light we are studying or about the processes it has undergone. The property of the density matrix of light prior to measurement that we want to measure also relies heavily on the measurement technique we employ. We can use a single-photon detector to measure the particle nature of light--the photon--the discrete quanta of the electromagnetic field. We can conversely measure the wave nature of the light field by making phase-sensitive measurements. In this thesis, we shall explore some advanced implementations and applications of these measurement schemes. First, we shall focus on a specific type of single-photon detector: the Superconducting-Nanowire Single-Photon Detector. We will first consider the integration of these detectors on optical waveguides, and discuss their optical characterisation. Then we will consider a practical application of these detectors by investigating a method to perform broadband spectroscopy with a single detector. We shall then progress to phase-sensitive measurements, and consider the intermediate regime between measuring the wave-like and particle-like nature of light. First we will perform a fundamental investigation of the transition between both measurement regimes. We will see how varying the phase reference itself allows us to tune between both regimes. Following this we will discuss an application of this intermediate regime, by considering an experimental setup to perform state tomography with a weak phase reference. The final consideration of this thesis will be a theoretical benchmarking scheme for a practical application of quantum optics. The manipulation of certain quantum states of light followed by a photon-number measurement can have practical applications in a variety of fields, and therefore validating the results is of extreme importance. On this final topic, we will discuss an experimentally friendly technique to benchmark the output of such measurements by considering smaller subsystems, and the practical requirements of this technique.

In linear optics, the concept of a mode or eigenmode is well established. Often these modes correspond to a set of fields that are mutually orthogonal with intensity profiles that are invariant as they propagate through a given optical system. More generally, using an eigenmode decomposition, one can define a set of orthogonal modes with respect to an optical measure given that is linear in the intensity of the fields or Hermitian in the fields themselves. However, if the intensity of the light is sufficiently large, the dipole response of an optical medium includes nonlinear terms that cause the eigenmode decomposition to break down. In this work, we introduce the eigenmode decomposition in the presence of these nonlinear source terms by introducing small perturbation fields whose interaction is mediated by some high-intensity background field. Unlike the eigenmodes of linear optics, these novel modes correspond to a set of orthogonal fields that are, in general, distributed across multiple wavelengths. Here, we study the definition and interaction of these eigenmodes for classical electromagnetic fields and multiphoton fields. In the context of classical fields, with our eigenmodes established, we highlight the influence of the high-intensity background field on the symmetry of the eigenmodes. At the multiphoton level, we show that the description of multiphoton fields is simplified by using the propagation eigenmodes while remaining equivalent to the standard approach.

A longstanding goal in quantum optics has been to realize a photon-number-resolving detector that efficiently counts the number of photons in an optical field. This goal has been largely met with the development of transition edge sensors which can count up to roughly 20 photons with efficiencies over 95%. This thesis presents three experiments that employ these detectors to characterize and prepare quantum states of light. Firstly, we develop a weak-field homodyne detector. By replacing the photodiodes conventionally used in homodyne detection with transition edge sensors, we experimentally implement a versatile measurement device that can tune between photon counting and quadrature measurements. We study the transition between these complementary measurement regimes and determine the minimum local oscillator strength needed to perform quadrature measurements. Secondly, we use the weak-field homodyne detector as a quantum state engineering tool. We propose a scheme to prepare a wide range of definite parity states, including two- and four-component Schrödinger cat states of arbitrary size with nearly perfect fidelity. Thirdly, we perform optical interferometry using quantum states of light with the aim of surpassing the maximal precision achievable with classical light, i.e. the shot-noise limit. We propose and experimentally implement a scheme that uses high-gain squeezed vacuum sources and transition edge sensors to prepare loss-tolerant entangled states containing up to 8 photons. While our achieved precision does not unconditionally (i.e. without post-selecting on certain measurement trials) surpass the shot-noise limit, our results do demonstrate the robustness of these entangled states to loss despite their size.

Quantum simulation is the notion of experimentally controlling and manipulating physical quantum mechanical resources such that their evolution can be mapped onto a problem that is much harder to solve by any other means. Realising a fully general quantum computer is still a work in progress but we can currently use devices that are purpose built to solve particular classes of problems, so called analogue quantum simulators, to investigate many-body quantum systems. In this thesis we first consider benchmarking the performance of realistic hardware implementations of quantum simulators through simulations of many-body dynamics, where we are able to demonstrate that even with current levels of experimental errors, analogue simulators in ongoing experiments are able to out-perform the best classical algorithms. We next propose how to use these devices in order to study strongly correlated phases induced by interactions in topological band structures, where we place a strong emphasis on how to experimentally realise, prepare and detect these phases for atoms in a Creutz ladder and in a Lieb lattice. We find that in these systems there is an enhanced tendency for interaction induced pairing, allowing for novel pair superfluid phases to be prepared in experiments with ultracold atoms. Finally, we consider additions to these simulators such that they map more closely to many-body systems in realistic solid state settings by including dissipative mechanisms. Specifically, we demonstrate that we are able to classically simulate this behaviour by modifying and hybridising existing numerical methods to allow for the simulation of open many-body systems beyond the Born-Markov approximation. We benchmark this numerical approach by simulating the dynamicsof electrons coupled to a phonon environment, where we find substantial qualitative differences compared to standard open system techniques.

This thesis describes the modifications that made to an evanescent wave fibre optic transducer with a lock-in detection for colorimetry to be a fluorimetric transducer. This includes 'side illumination' as a superior excitation mode compared with the evanescent wave excitation of fluorescence. Specifically, side illumination results in a strong fluorescent signal and very low (negligible) exciting light coupling into the optical fibre, therefore, it serves mostly as a fluorescent signal source rather than noise. The modified transducer is designed to be versatile; easily adapted for either waterborne or airborne analyte sensing. In addition, it can be also used to detect changes in fluorescence from either a sensitiser film or solution and can be applied for sensing applications even when the sensitiser degrades under the exciting light. Moreover, the transducer does not require a fluorescence spectrometer. As a test of the transducer and to prove its versatility, it was applied in airborne and waterborne sensing, with minimal adaption between these media. This was done by exposing the spray-coated stripped section of the glass optical fibres with polymer poly(phenylenevinylene) derivative poly[2-methoxy-5-(3',7'-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV) as a fluorophore, to the nitro-aromatic explosive dinitrotoluene (2,4-DNT) as an analyte, in both air and water media. Limit of detections (LoDs) of 0.48 ppb and 56 ppb were obtained for airborne and waterborne DNT respectively. These LoDs are ~ 62 times below previously reported values for DNT detection using PPV derivatives, as well as 3.3 times below LoDs for DNT sensing with different sensitisers. A pyrazolyl chromene derivative known as Probe 1 was successfully used as the fluorescent sensitiser in a solid film form, thereby enabling its use for the detection of waterborne Cu2+ and thus avoiding the exposure to harmful solvent during sensing experiments. Specifically, a Probe 1 film was prepared via its immobilisation in a plasticised polyvinyl chloride (PVC) acting as a phase transfer membrane. It was then dip-coated onto the stripped section of an optical fibre before its exposure to a range of waterborne Cu2+ concentrations. The LoD of Cu2+ was 0.43 µM, below the potability limit, and is also 3.7 times lower than the LoD measured by a conventional spectrofluorimeter based on the same sensitiser. The good solubility and long-term stability of Morin derivative NaMSA known as an 'off ? on' fluorescent sensitiser for Al3+ in water, enabled it to be used in aqueous media avoiding the need for phase transfer membrane preparation. The dissolved NaMSA was used in conjunction with our fibre optic transducer to detect Al3+ in drinking water below the potability limit. Moreover, the concentration of Al3+ was reliably quantified in a range of samples by using the standard addition method. It is known that morin-based Al3+ cation sensors can be selectively recovered by being exposed to fluoride (F- ) anions. This method was further developed to enable complementary sensing of either fluoride anions, or aluminium cations using the same dye in both cases and achieving sub-micromolar LoDs. The transducer demonstrates a high figures-of-merit compared with previous reports on both aqueous Al3+ cation and F- anion sensing.

The object of this work is the development of more highly efficient and practicable quasi-optical devices for use in the THz range of frequencies. Most tech- niques already developed for use at lower and higher frequencies are not readily adapted for use in this range due to material and propagation constraints. The introductory chapter gives an overview of some of these problems and the layout of the thesis as a strategy for improving the situation. Chapter 2 gives the more relevant theory that is applicable to this work. This includes physical optics, the behaviour of individual meshes, and the behaviour of accurately spaced mesh stack devices. Chapter 3 addresses the problem from a design point of view where an outline of a fully automatic program for achieving optical design goals is presented. Chapter 4 addresses improvements achieved by developing the manufacturing process. This includes fabrication of individual meshes and their combination into full filtering devices. Methods of assessing these devices are also addressed. Chapter 5 considers the design philosophy of a real world project where the ad- vantages of mesh filters are used in conjunction with other filter types to produce an astronomical CMB measuring spectrophotometer for use on a ground based high altitude telescope. Finally, progress is assessed with avenues for further work and several open questions being considered. The appendices include sections on what types of filters exist, the geometric properties of filtering, general filter quality factors, applications of spectral filtering, spectral filtering mechanisms, high frequency removal, a paper illustrating filter system implementation, and pressure window design.

Rapid advances in the field of ultrafast science have led to the creation of isolated attosecond light pulses and pulse trains in the vacuum ultraviolet (VUV) and extreme ultraviolet (XUV) spectral regions. This has opened the possibility for the observation of electronic processes on the attosecond time scale with the technique of attosecond photoelectron spectroscopy. With its expansion to the condensed phase, it allows the investigation of collective electronic processes on atomic length scales with unprecedented time resolution, probing dynamics such as electronic screening, plasmonic excitations and electron transport. An enhanced understanding of these processes is of importance for optoelectronics, catalysis and light harvesting. However, due to both the experimental complexity of such measurements, and the range of possible dynamics occurring simultaneously, isolation of the contribution of a particular dynamical process to the experimental measurement is extremely challenging. New developments in the technique of attosecond photoelectron spectroscopy are therefore required. In this thesis, I describe three developments to the attosecond photoelectron spectroscopy capability. A phase-stable two-colour source was developed, allowing for the possibility of studying the wavelength dependence of the ultrafast field response at the surface. A gas-phase demonstration of the two-colour streaking capability is presented, as well as the creation of XUV attosecond pulses of enhanced flux through a two-colour field synthesis. An experimental scheme for the direct comparison of attosecond valence photoemission from two metal films, Au and Ag, was implemented with experimental results indicating that this scheme can eliminate systematic errors arising from the Gouy phase. Utilizing the capability to produce isolated attosecond pulses at both 20 eV and 93 eV, an experiment investigating VUV-XUV photon energy dependence of attosecond photoemission from Au films is presented. Finally, possibilities for future work utilizing these developments to study the material and wavelength dependence of attosecond photoemission from surfaces are discussed.

Transformation optics is a new and highly active field of research, which employs the mathematics of differential geometry to design optical materials and devices with unusual properties. Probably the most exciting device proposed by transformation optics is the invisibility cloak. However, transformation optics can be employed in many other cases, for example when designing a setup mimicking a curved space-time phenomena in a lab. The purpose of this thesis is to establish a new concept of transformation optics: instead of designing complicated materials, we will design our devices using standard optical elements such as lenses or optical wedges. We will stretch the possibilities of geometrical optics by providing a novel description of imaging due to combinations of tilted lenses and the theory of invisibility with ideal thin lenses. This theory will be then applied to design novel transformation optics devices, namely the omnidirectional lens and a number of ideal lens invisibility cloaks. We also present a new approach of building optical systems that simulate light-field propagation in both 2D and 3D curved spaces. Instead of building the actual curved space, the light field is regarded to travel in the respective unfolded net, whose edges are optically identified, using the so-called space-cancelling wedges. By deriving a full analytical solution of the Schrodinger equation, we will also investigate a quantum motion in a number of two dimensional compact surfaces including the Klein bottle, Mobius strip and projective plane. We will show that the wavefunction exhibits perfect revivals on these surfaces and that quantum mechanics on many seemingly unphysical surfaces can be realised as simple diffraction experiments. Our work therefore offers a new concept of optical simulation of curved spaces, and potentially represents a new avenue for research of physics in curved spaces and simulating otherwise inaccessible phenomena in non-Euclidean geometries. We conclude with a summary of potential future projects which lead naturally from the results of this thesis.

This thesis examines different approaches towards achieving greater luminescence efficiencies in colloidal nanocrystal quantum dots with primary focus towards application within singlet fission photon-multiplier down-conversion systems. Specific challenges to characterising their luminescent properties have been explored in detail, also applicable to other luminescent materials. Additionally, alternative applications for luminescent quantum dots have been investigated, and finally, the gap between small-scale synthesis and industrial production was explored for the material system of most interest. PbS quantum dots were synthesised and their luminescence efficiencies were enhanced through cation exchange with cadmium. It was found that the luminescence improvement was sensitive to a multitude of factors, particularly reaction duration at hitherto unexplored short timescales. Time-resolved optical and structural characterisation was performed indicating a two-step mechanism consisting of cation adsorption followed by subsequent exchange. Halting the reaction to the adsorption stage resulted in the highest luminescence efficiencies. The lead-free quantum dot systems InAs and CuInSe2 were investigated as alternative near-infrared emitters for photon-multiplication. Core-shell approaches with a variety of materials and complex structures were employed to improve their otherwise poor luminescence. The measurement of photoluminescence quantum efficiency is widely used for luminescent material characterisation. As a figure of merit for colloidal quantum dots, the method was examined in great detail. The sources of systematic error were identified and random measurement error quantified for a recognised measurement methodology in order to obtain accurate measurements with meaningful uncertainty bounds, applied for a photon-multiplier demonstrator system. CdSe and InP core-shell quantum dots were synthesised for a novel voltage probe. Their stability under electrolytic environments and strong response to applied electric fields was demonstrated for a biological voltage sensor. PbS quantum dots were synthesised using a commercially-available microfluidic flow reactor. The challenges to product quality and reproducibility upon scale-up were examined. Mitigation strategies against the problems encountered were proposed.

The human eye has various aberrations that distort the image formed on the retina. Monochromatic aberrations are the distortions present at a single wavelength and chromatic aberrations are wavelength dependent. Longitudinal chromatic aberration (LCA) describes the difference in defocus at different wavelengths. The LCA of the human eye is approximately 2 dioptres (D) across the visible spectrum. Normally we are unaware of these distortions, however, they do play an important role in our vision. The aim of this thesis was to investigate the importance of these aberrations in the context of the modern world. The illuminant spectra that we are exposed to today are quite different from 100 years ago. Because LCA results in a difference in defocus with wavelength this means that the amount of defocus blur in the retinal image will change depending on the spectrum of light. In this thesis findings are reported indicating that there are certain illuminant spectra for which the chromatic fringes due to LCA were more visible. We also investigated how people accommodated to spectra made up of two distinct narrowband LEDs. The findings suggest that people do not accommodate optimally to these spectra. There is also increasing interest in blurring stimuli realistically. This is partly with the emergence of virtual reality, so that 3D scenes appear as realistic as possible, but also has more clinical applications in trialling the effects of different corrective lenses on vision before the lenses are made (or inserted in the case of intraocular lenses). We investigated the importance of including monochromatic aberrations when rendering out of focus stimuli. It seems that monochromatic aberrations do make the stimuli appear more realistic, however, they did not have a significant impact on visual acuity.

We present the design, fabrication, and operation of a new genera-tion of thermal alkali vapour nano-cells. The nano-cells include in-ternal structures with length scales 200−2000 nm created by laserlithography and reactive ion etching. The assembly process adoptsoptical contact bonding and glassblowing, avoiding the requirementfor any bonding agents or adhesives. We demonstrate a novel methodfor characterising the size of the internal vapour nano-channels. Thedesign allows for greater optical access and compatibility with highnumerical aperture (NA=0.7) optics; we demonstrate this with totalinternal reflection fluorescence spectroscopy and high resolution ima-ging of the nano-channels. Additionally, we report for the first time onthe photon statistics of light from a thin atomic ensemble. Finally, wediscuss the diffusion of atoms inside confined geometries with a num-ber of detection methods, and investigate options for controlling andmanipulating the atomic density and its diffusion. In total, we presentour new nano-cell design as a significant advancement of the field andpropose its use in scalable atomic and quantum optics applications andtechnologies.

The field of laser beam shaping advances the study of optics by pushing the limits of structured light and its applications. This thesis aims to exploit classical optical theory using state of the art structuring techniques to introduce two novel demonstrations: (1) high-speed digital micro-mirror device (DMD) light shaping and (2) broadband dual spatial light modulator (SLM) arbitrary vector beam shaping. These shaping techniques are also employed to demonstrate the fundamental group delay of structured light in free space, for Bessel and focused Gaussian beams. Motivation for the structuring of light in both scalar and vector regimes is explained for a wide range of applications, from optical fibre communications and microscopy, through to computational imaging and micro-manipulation. The thesis continues by providing an in-depth background to the relevant principles of optical wave theory, and provides an overview of holographic beam modulating techniques to be used thereafter. The first key result in this thesis is the high-speed (4kHz) generation of arbitrary vector beams using a DMD, by way of tuning the intensity, phase and polarisation of the light. Widely used vector profiles such as radial, azimuthal, uniformly circular polarisations and Poincare beams are characterised using spatially-resolved Stokes parameters. The intention is to promote the DMD as a cost-effective SLM which provides a switching rate that is up to ~2 orders of magnitude faster than competing liquid crystal (LC-)SLMs. Extended details into the practical considerations of using a DMD as a diffractive optical element are discussed. The second result in this thesis is the broadband (100nm) generation of arbitrary vector beams using a pair of LC-SLMs in tandem. The wavelength-dependent dispersion of diffractive optics is a major issue in the beam shaping of broadband light; the system presented in this thesis employs a second dispersion-correcting SLM within a Sagnac interferometer. The vector beam profiles from the previous result above are reproduced across four wavebands within the 100nm range. Furthermore, the effects of chromatic dispersion in both DMDs and LC-SLMs are investigated, as is the use of in-situ wavefront correction in beam shaping systems. In the final investigation reported in this thesis, the fundamental group velocity delay of structured light in free space is demonstrated in a classical interferometer. An elegant and novel approach is presented, which interferes one Gaussian beam with another which has, at some point in its propagation, been structured and then destructured by two LC-SLMs in tandem. The associated reduction of group velocity arises from the free space boundary conditions associated with structured beams, which in turn affects their wavevectors; this effect is demonstrated for Bessel beams and focused Gaussian beams using a simple interferometric approach. The delays detected are on the order of 1 micron over 10cm. Furthermore, the structuring and destructuring of beams with many constituent wavevectors (c.f. optical speckle) is presented, and its delay is theorised in anticipation of future studies. It is intended that this thesis serves as a comprehensive account of the practicalities of vector beam shaping in different regimes for potential applications, bolstered by meaningful investigations to unearth the true nature of structured light and its properties.

In this thesis I discuss the experimental demonstration of quantum-enhanced imaging and sensing schemes able to surpass the performance of their classical counterparts. This is achieved by exploiting the spatial properties of quantum correlated biphotons. Over the next chapters I first discuss the production and detection of quantum correlated photons using a type-I nonlinear crystal and a single-photon sensitive electron-multiplying CCD camera. I then provide a simple yet powerful description of the spatially resolved detection of biphotons, allowing to accurately model and assess the performance of the quantum-enhanced schemes featured in this thesis. These consist of a shadow-sensing and an imaging scheme able to respectively beat the shot-noise-limit in the optical measurement of the position of a shadow and the diffraction limit in the full-field imaging of real-world objects. A combination of simulated and experimental results are used to investigate both the achieved and theoretically available quantum advantage. Optical losses and detector noise are found to limit the better-than-classical performance of the schemes, which rely on the ability to jointly detect an as high as possible number of spatially correlated biphotons.

The isolation and study of graphene has led to research into a large number of other atomically thin, two-dimensional (2D) materials. These materials have various fascinating properties that complement those in graphene; allowing for the building of designer van der Waals heterostructures. However, many of these 2D materials are unstable in ambient conditions, restricting their study. In this work, methods to isolate and protect these materials in an inert argon environment are given; revealing novel insights into the optical properties of few-layer, air-sensitive 2D semiconducting materials and their heterostructures. Specifically, the lack of degradation due to encapsulation enable the observation of Raman spectra and second harmonic generation in monolayer InSe as well as Raman and photoluminescence spectra for few-layer GaSe crystals for the first time. These isolated 2D semiconductors are then stacked adjacent to one another, forming heterojunctions with a type-II band alignment. These heterojunctions reveal new interlayer excitonic states with an energy that may be tuned by select- ing the layer thicknesses. The recombination of these exciton states is suggested to be direct or quasi-direct in momentum-space, in contrast to previous attempts that demonstrated momentum-indirect interlayer excitonic states in 2D semicon- ductors. These momentum-direct interlayer excitons show bright luminescence and, as their energy is tunable, increase the spectral coverage available for van der Waals heterostructures. Lastly, the high quality fabrication methods presented also enable the first observation of resonantly hybridised excitons between two closely aligned TMDC monolayers. The close crystallographic alignment promotes the hybridisation of interlayer and intralayer excitonic states, revealing new states that inherit the properties of each excitonic component.

Many developments in modern physics rely on the understanding of quantum systems that are strongly coupled to complex, structured environments. In particular, quantum emitters such as single molecules and quantum dots are of great interest in many applications in photonics, solar energy and nano-electronics. In many of these situations, the traditional tools of quantum optics break down, requiring a non-perturbative approach to system-environment coupling. Understanding strongly-coupled open quantum systems is still an active area of research, with many powerful numerical and analytical techniques being developed. In this thesis, we attempt to combine the approaches of strongly-coupled open quantum systems with the study of natural and artificial solar energy conversion. Light-harvesting systems are highly non-equilibrium in nature, since they interact with multiple environments at different temperatures - a regime which is difficult to treat with many cutting edge open systems techniques. Starting from the simplest possible model, that of a single transition in a molecule, we uncover some common inconsistencies that get made in the literature and develop further the notion of 'environmental non-additivity'. We show that this effect, where the coupling of a quantum system to one environment affects how it couples to another environment, is a general property of many non-equilibrium models. We see that for sufficient phonon-coupling it can directly lead to population inversion in a two-level emitter under incoherent thermal driving. After analysing the two-level case, we then expand the model to include two interacting emitters. This builds on the previous work in the literature on excitonic energy transfer, in order to more realistically evaluate the effectiveness of these systems within a quantum photocell context. Using non-perturbative open systems techniques, we demonstrate a striking diversion from the weak-coupling theory in the resultant dynamics and steady-states. Finally, we derive a novel model for a molecular photocell, which allows us to explore the interplay between strongly-coupled vibrations, photon absorption and molecule-electrode coupling. This setting gives rise to an array of rich non-additive phenomena, which ultimately determines the photocell performance. We identify regimes where strong phonon-coupling enhances photocurrent.

Light and heat are synergistic tools used in the manipulation of nanoparticles and biomolecules. When optical effects dominate over thermal effects, the motion of nanoparticles can be controlled by optical forces. Here, we study the motion of 100 nm gold particles within a 1D optical potential, created by interfering counterpropagating beams. Tracking of particle trajectories revealed a large and asymmetric reduction in the nanoparticle diffusion constant in the presence of the traps, in agreement with theoretical predictions. When thermal effects dominate, laser light can induce local temperature gradients. Here, this was achieved by absorption of near-infrared (NIR) laser light in a Chromium microdisc. This resulted in thermophoretic separation of sodium azide ions, causing a local electric field that was used to manipulate 26 nm polystyrene beads. The nanoparticles were observed to follow the NIR heating spot, enabling light-controlled nanoparticle swarming. The induced 3D temperature profiles were characterised by time-correlated single-photon counting microscopy, with a temperature-sensitive dye. Through analysis of the particle velocities, the thermoelectric field strength, as well as the previously unknown Soret coefficients of azide ions were quantified. Transmission of laser beams through nanoparticle suspensions can lead to strong nonlinear lensing and soliton-like propagation effects. Literature has attributed these to redistribution of particles by optical gradient forces, and the effect is commonly described as an effective Kerr nonlinearity. To test this hypothesis, beam propagation experiments through a suspension of 40 nm plasmonic gold nanoparticles were carried out, and were found to be in agreement with previously reported results. To verify the nature of the effect, a new time-resolved z-scan technique was developed to measure the timescale and magnitude of the refractive index change. Surprisingly, the data demonstrates that the timescales can only be explained by thermal-absorption, -diffusion, and thermo-optic effects. As a result, the nonlinear effects are non-local and z-scan measurements will underestimate their magnitude.

Atom interferometry allows for new precision limits in measurement and a key component of it is the beam-splitter. In this thesis we look at the properties of an all optical beam-splitter, which is created by the overlap of two Gaussian laser beams,which also function as waveguides for the Bose-Einstein condensate. For this mainly the split step Fourier method is used to model the propagation of a low density Bose-Einstein condensate of atoms. The two main areas of interest are the splitting and recombination properties. The splitting is studied both in two and one dimensions. For the one-dimensional case both standing and propagating waves are used to find the ideal splitting conditions of a balanced splitting and transmission. The result of these methods are in general agreement with the exception that for the propagating wave some of the atoms can become localised inside the beam-splitter. For the propagation it was found that the splitting is not perfectly coherent as the outputs are slightly deformed. However, when looking at the two-dimensional case we see that the splitting is not even close to being coherent. This is because the beam-splitter excites the incoming wave into higher transverse modes of the waveguides. To compensate for this the depth of the waveguides was lowered and the width narrowed to reduce the potential kinetic energy that the atoms could acquire and to increase the separation between the eigenstates to lower the probability of excitation into higher modes, respectively. Nonetheless, these investigations improved the splitting balance but it is still not coherent. Another method investigated was the introduction of a third laser which acts as a filling to reduce the depth of the potential well where the lasers generate the beam-splitter. This approach does not improve the splitting. Hence instead of recombining single mode waves we used a multimode approach. For this we found that the mirror position is crucial for certain parameters as the longitudinal momentum is not necessarily the same in the reflection and transmission waveguide. Our investigations have generated interference fringes in this model system with a fractional height up to 33%.

In recent years considerable research focus has been directed to graphene like materials that display properties that are similar to the excellent physical, chemical and mechanical characteristics of graphene. In this respect, one major research area is the reduction of graphene oxide (GO) and especially the laser reduction of graphene oxide. The main aim of this thesis was to develop, construct and test an experimental system to create laser reduced graphene oxide films, and to classify the degree of reduction by measured changes in the surface characteristics, conductivity and resistance, and chemical composition of the surface. The objective was to achieve laser reduced graphene oxide with optimum high-quality graphene like features. A system was developed using an Nd:YVO4 laser with wavelength 1064nm and was successfully used to create reduced graphene oxide with the findings compared, with some success, to theoretical predictions and those of other researchers. Many researchers have completed major experimental programmes that involve time consuming, expensive and repetitive tests where systematic and incremental changes are made to a large number of variables to establish the optimum characteristics of the degree of reduction. To avoid such repeat testing a primary objective of the thesis was to develop a system that yielded the optimum information from a single test. Such an experimental setup was successfully developed, and the resultant pattern of reduced graphene oxide was termed a z-scan. The z-scan pattern was created by a range of fluence values which ranged from below the threshold value to create reduction through to those that caused full ablation of the surface. Good agreement was observed between the experimental results and the predicted pattern of the damage threshold which was observed at a fluence of 13.8 mJcm−2. To better understand the quality of the reduced GO at points over the surface of the z-scan a further series of tests with large area irradiated surfaces at different fluence values were completed. The roughness of these irradiated large area samples was independent of fluence but was enhanced by an order of magnitude when compared to that measured for GO. The conductivity of the irradiated sample was shown to increase with increase in laser fluence in an almost linear way. Raman spectra demonstrated the usual D, G and 2D peaks and, in line with other researchers the reduction was interpreted by the ID/IG and I2D/IG ratios. As fluence was increased the relationship between the ID/IG ratio had an overall downward trend in the range 1.21 to 0.75 with a flattening of the relationship at 0.75 corresponding to a fluence circa 35 mJcm−2. Examination of the I2D/IG ratio showed that there was a gradual increase from a value of 0.23 to 0.31 but in this case with a saturation value at a fluence circa 32 mJcm−2. Hence it was concluded that a fluence in the range 32 mJcm−2 to 35 mJcm−2 resulted in the optimum reduction of the GO. Similarly, the XPS results recorded a significant change in the carbon and oxygen species in the GO and rGO. The oxygen content was shown to reduce significantly at a fluence of ~35 mJcm−2 with a flattening off at higher values of fluence to a constant value. A corresponding increase in the C-C carbon occurred and the carbon/oxygen peak ratio increased significantly in the range 29.1 mJcm−2 to 36.5 mJcm−2 with an overall increase from 3.5 at a fluence of 21.8 mJcm−2 to 13 at a fluence of 46.0. These results confirm that at a fluence in the range 30 – 35 mJcm−2 the degree of reduction is sufficient to transform the carbon and oxygen species with the reduced GO having graphene like characteristics. Temperature changes were also identified as a major factor to influence the reduction process and a temperature model, based on the theory of Yakovlev et al., 2019, has been described. The model predicted significantly high values at the centre of the laser beam but there was a rapid reduction in temperature in a radial direction away from the centre. Good agreement was observed between the predicted temperature and the boundary of reduced GO of the z-scan which was shown to occur at a temperature of circa 210°C. Tests were also completed to establish the wettability of the irradiated surface and it was observed that the wettability contact angle increased with increase in laser fluence. Values increased in an almost linear way, but values increased from 46° for GO to a maximum value of 84° for the rGO. These values compare well with the results of other researcher who have used similar irradiated surfaces. As the surface roughness was independent of fluence the increases in contact angle were attributed to the changes in the chemistry of the surface. Based on the outputs of the surface chemistry analysis for optimum reduction at a fluence in the range 32 mJcm−2 to 36 mJcm−2 the corresponding contact angle was circa 80°. In summary it was concluded that the experimental facility successfully met the overall aim of the thesis and provided an efficient and reliable one step technique to establish the optimum range of laser fluence to create good quality rGO, supported by physical, electrical and chemical results.

The work in this thesis describes interesting phenomena that results from the interaction between high intensity laser light and nonlinear matter. By changing the structure of light's properties such as intensity and polarisation as well as the type of nonlinear action that occurs during propagation through the medium, we aim to describe how the properties of light are affected by the various interactions. Considering down-conversion in a second order x(2) medium we first present a spatiotemporal mechanism for producing two dimensional optical rogue waves in a turbulent state driven by vortices with helical wavefronts. Self-organising hexagonal structures bound in phase lose stability and synchronised oscillations are unstable leading to phaseunbound vortex-mediated turbulence with high excursions in amplitude. Nonlinear amplification leads to rogue waves close to optical vortices, and probability density functions typical of rogue waves. We then consider fully structured light (FSL) within a Kerr x(3) medium. In particular, we describe how the polarisation distribution of FSL beams is affected by propagation. In the linear case we derive an expression for the rotation of the polarisation and show the rotation is due to the difference in Gouy phase between the two eigenmodes in the beam. For nonlinear propagation we show the effect of the cross-phase modulation from self focusing results in additional rotation that can be controlled by changing various physical parameters of the FSL beam like the beam waist and magnitude of OAM. Finally we consider the interaction with the Kerr medium in an optical cavity. Above Turing threshold we observe the formation of peaks upon the FSL structure. Where the beam carries a net orbital angular momentum we observe a rotation in the structure. We detail how the angular velocity of the Turing structure can be controlled by careful selection of the parameters of the FSL beams.

Lanthanide-ion-doped upconversion nanoparticles (UCNPs) have emerged as a new class of luminescent materials that offer excellent chemical stability, good biocompatibility, narrow bandwidth, long luminescence times, good resistance to photobleaching and photoblinking. 1,2 Most importantly, UCNPs can up-convert two or more low energy photons into one high energy photon because of their intra-configurational 4f electron transitions. 1,2 Therefore, UCNPs are of great interest in many fields including photocatalysis, biomedicine and sensing.3 In this project the main aim was to explore the UCNPs synthesis under different conditions and their functionalization with organic and inorganic materials. We observed that the synthesis played a critical role in determining the structure, phase, and upconversion (UC) luminescence of the resulting materials. Different parameters including the role of oleic acid (OA) and the effect of the host lattice and the fluoride source were studied. Furthermore, different coatings materials were formed around the surface of the core UCNPs and were fully characterized. With a view of developing a universal protocol for the silanization of UCNPs, we investigated the silica coating around different sizes and morphologies of UCNPs. We created an approach based on a calibration curve. The employment of this approach proved to produce uniform and individual silica coating of the UCNPs, which were employed for further functionalization with oligonucleotides and gold. The synthesis and the photocatalysis activity of the UCNPs coated by TiO2 were studied. Results showed efficient photocatalytic activity under UV as well as IR irradiation, using redox dyes (DCPIP and Resazurin). Different effects on the photocatalytic activity such as annealing effect, loading effect, and recyclability were also studied. Additionally, we functionalized the surface of the UCNPs with IR-806 dyes in order to enhance the UC luminescence properties and to provide new insights on the energy migration and surface effects of the UCNPs. Hence, the UC and downconversion (DC) luminescence properties were individually investigated in the dye-sensitized UCNPs in comparison to the non-sensitized UCNPs. Encouraged by the principle of dye sensitizing in UCNPs, we additionally investigated whether new IR dyes could be used to cover different part of the IR spectrum. We proposed a new IR-dye molecule (IR-1076) in order to alleviate the well-known concentration quenching that exist in UCNPs. Although the work is still ongoing, we expect that the strategy could be used to produce UCNPs with higher dopant concentrations, hence enhancing the UC and DC luminescence properties.

The work presented in this thesis aims to integrate sources and detectors of nonclassical states of light into a single photonic chip. Correlated pairs of single photons are among the most used sources in many quantum optics and quantum information experiments but their integration with detectors still remains a challenging task. In the first part of the thesis we exploit the generation of correlated pairs of photons in the visible spectrum using an integrated Silicon Nitride microring resonator. As the fabrication process of our sources is fully compatible with back-end CMOS technology, we also discuss the unique possibility of integration with silicon avalanche photodectors to provide a platform for commercially available, fully integrated, analogue quantum simulator working at room temperature. The drawback of universal quantum computation with single photons is its probabilistic nature that increases the technological complexity to obtain complete on chip integration of all necessary components to prepare, manipulate and measure quantum states of light. On the other hand, quantum information processing with continuous variables is completely deterministic. Therefore, in the second part of this work we report design, fabrication and experimental verification of an integrated source of broadband squeezed state of light on a photonic chip. We numerically investigate the amount of obtained squeezing and spurious noise that prevents us to observe shot noise reduction at short sideband frequencies. Additionally, we propose a design to extend our work towards hybridization with discrete variables to obtain qubits that can be protected against errors.

This thesis presents the experimental scheme for a guided cold atom Sagnac interferometer. Although atom interferometers have become an established method for precision measurements, a feasible clock-scheme based on fully guided atoms has yet to be realised. Radio frequency potentials, generated by a chip, provide a means to create a compact, fully controllable guided atom interferometer. The experimental infrastructure for a rubidium cold atom system is built and characterised. A chip-based atomic clock scheme is presented, utilising state-dependent guiding around a ring shaped trap. The chip design to form the trap and operate the interferometer is presented, and a vacuum compatible PCB has been designed and commercially manufactured to provide atomic transport and compression towards an atom chip. This project is part of the larger MatterWave project. In collaboration with Birmingham and Crete, the Matterwave project aims to develop ultra-sensitive matter-wave interferometry for compact devices.

In this work, the design and implementation of a Multi-Experiment Spectral Suite (MESS) is described. The MESS currently contains two time-resolved experiments - Transient Absorption (TA), and Second Harmonic Generation (SHG) - but has been designed with a view to expansion. The primary species of interest to be studied is the hydrated electron. As an electron is generated during water ionization, its hydrated form is significant within many scientific processes including, but not limited to, biological chemistry and tissue damage, atmospheric chemistry and nuclear chemistry. However, the majority of what is known about the hydrated electron is its behaviour in a bulk solvation environment with little understanding known about its behaviour at interfaces where it reacts in most instances. The MESS provides the ability to build a bottom up picture of solvation environment on molecular dynamics in going from the bulk (TA) to the interface (SHG). SHG enables the study of interfacial dynamics due to its inherent surface sensitivity. The method described here is an improvement on a previous phase-sensitive SHG technique that varied the phase of the interference between the SHG from a sample (ESHG) and a local oscillator (ELO) manually by incrementally changing the distance between the sample and reference sample. The new technique presented here is able to record the entire interference pattern in a single shot by using a phase varying unit comprised of a Reference Surface sandwiched between two glass wedges. The technique is characterised in this work by studying the excited state dynamics of malachite green at the air/water interface, exhibiting excellent phase stability and sensitivity and comparatively short acquisition times. In comparison, the TA technique presented is experimentally simpler than SHG. The excited state dynamics of molecules are studied in which a pump pulse induces an excitation which is then probed by a white light pulse spanning 520-950 nm continuously. In combination with 30 kHz modulation of the laser, shot-to-shot pump-probe measurements are presented for both SHG and TA techniques.

Matter-wave interferometry has enabled high precision measurements of inertial forces such as gravity and the Coriolis force. This is facilitated by the long-term stability of the physical properties of atoms and lasers. Recent experiments have demonstrated the operation of portable, robust sensors using atom interferometry. This has potential uses in the context of inertial navigation, where conventional devices suffer from long-term drifts due to bias instability. Furthermore, determining position via dead reckoning requires minimisation of dead time between measurements. This thesis presents the development of an atom interferometer for measuring horizontal accelerations. In this configuration, gravity induces motion across the laser wavefront, which constrains the tolerable level of wavefront distortions. Effective control of the experiment allows the interferometer to be operated at a rate of 4 Hz. A cold ensemble of 10^6 atoms in the same internal state is prepared in 150 ms. The interferometer operates using a sequence of three laser pulses separated by T= 25 ms to achieve sensitivity to horizontal accelerations. Combining this with a classical accelerometer provides a method of correcting for vibration-induced noise, as well as determining the interferometer fringe order. After an integration time of 40 s, the sensitivity to horizontal accelerations is better than 3^-6 m s^-2. Effects which limit this sensitivity are discussed.

In recent years great progress was made in the spatial control of light with dynamic phase and amplitude modulators such as spatial light modulators and digital micromirror devices. In this work we describe the theory and practice of light shaping with such devices, detailing the spatial control of amplitude, phase and polarisation of coherent laser beams. We use our expertise in generating and measuring light fields with spatially dependent polarisation structures to characterise the correlations between spatial modes and polarisation in such light fields. We do this by adapting concurrence, a quantum measure of entanglement, to these classical correlations. One of the most promising application of coherent laser light is in the control of atomic media via atom-light interactions. In this work we describe the construction of simple external cavity diode lasers designed for the generation of resonant light for atomic physics applications. We exploit these lasers and spatial light modulators to create and measure three-dimensional atomic population structures in a warm rubidium vapour. We also implement a magneto-optic and a dynamic dark spontaneous-force optical trap for rubidium. These traps produce dense (~ 10^11 cm^-3) and cold (~100 uK) clouds of rubidium atoms. We develop the theory of spatially dependent electromagnetically induced transparency in such traps using rate equations. We find that the absorption of linearly polarised light depends on the relative direction of a magnetic field and the light polarisation. We use the cold atom clouds to measure the direction of magnetic fields by using this dependence and laser beams with structured polarisation.

Scattering media have traditionally been seen as a hindrance to the controlled transport of light through media, creating the familiar speckle pattern. However such matter does not cause the loss of information but instead performs a highly complex deterministic operation on the incoming flux. Through sculpting the properties of the incoming wavefront, we can unlock the hidden characteristics of these media, affording us far more degrees of freedom than that which is available to us in traditional ballistic optics. These additional degrees of freedom have allowed for the creation of compact sophisticated optical devices based only on the deterministic nature of light scattering. Such devices include diffraction-limit-beating lenses, polarimeters, spectrometers, and some which can transmit entire images through a scattering substance. Additional degrees of freedom would allow for the creation of even more powerful devices, in new working regimes. In particular, the application of related techniques where the scattering material is actively modified is limited. This thesis is concerned with the use of optothermal nonlinearity in random media as a way to provide an additional degree of control over light which scatters through it. Specifically, we are concerned with silica aerogel as a platform for this study. Silica aerogel is a lightweight skeletal structure of silica fibrils, which results in a material which is up to 99.98 % by volume. This material exhibits a unique cocktail of properties of use such as near unitary refractive index, an order of magnitude lower thermal conductivity, and high optothermal nonlinearity. The latter two of these properties allow for the creation of localised steep thermal gradients, proportionally affecting the low refractive index significantly. Additionally through differing fabrication steps, the opacity, and as a result, we can adjust the scattering strength. In line with the development of light deterministic light scattering techniques in linear media, we develop through the use of pump-probe setups, a framework for the development of a similar line of techniques in nonlinear scattering media. We show that we can reversibly control the far-field propagation of light in weakly scattering silica aerogel. Following this, we show that nonlinear perturbation can be used to extend and modify the optical memory effect, where slight adjustments in scattering direction maintain the overall correlation of the scattered profile. Finally, we measure the nonlinear transmission matrix, a complete description of how any wavefront would pass through at a particular point in a scattering media, and how that scattering can be modified through the application of an optothermal nonlinearity. Extending the tool of scattering media into the nonlinear regime helps pave the way toward the next set of advances in the field of light scattering control.

The first part of this thesis focuses on a novel design of photonic crystal microcavity coupled to InGaAs quantum dots. Such coupled dot-cavity systems can be used as enhanced single photon sources for quantum information applications and more complicated arrangements could even be used as optical switches in a quantum computer. A photolithography process is used to fabricate these cavities, allowing them to overcome many of the difficulties involved in achieving reliable dot-cavity coupling in traditional e-beam defined cavities. Theoretical FDTD simulations are used to predict the Q factor and mode volume (1.44 (λ0/n)3) of this cavity design. The fabrication process is given in detail, and micro-photoluminescence measurements are used to verify successful cavity fabrication. A success rate of 85% is achieved with Q factors as high as 7.4 × 103 at a wavelength of around 1.25 µm. These cavities are shown to have comparable performance to existing designs such as L3 and Notomi cavities fabricated using e-beam lithography. The second part covers studies of four different polycrystalline perovskite films with compositions of the form FA0.83Cs0.17Pb(BrxI1-x)3 and varying bromine fraction x ∈ {0.1, 0.2, 0.3, 0.4}. These perovskites are promising candidates for commercially scalable photovoltaic applications and have received a great deal of scientific interest over the past decade. This particular composition has been shown to have improved stability and optoelectronic properties compared to other perovskites. Micro-photoluminescence mapping is used to study the temperature dependence and structure of these samples. The diffusion lengths are found to be in the range from 2 µm to 5 µm, and evidence of photon recycling over longer distances is identified. Time-resolved photoluminescence measurements are carried out at cryogenic temperatures to study the carrier decay dynamics. A theoretical model of the decay process is developed and fitted to the data. Both excitons and free carriers are found to contribute to the emission, with the 10% bromine sample having the highest exciton binding energy.

This DPhil thesis presents two key works towards practical applications of quantum optics. Both works are novel and achieve competitive state-of-the-art results. Today's most widely used method of encoding quantum information in optical qubits is the dual-rail basis, often carried out through the polarisation of a single photon. On the other hand, many stationary carriers of quantum information | such as atoms | couple to light via the single-rail encoding in which the qubit is encoded in the number of photons. As such, interconversion between the two encodings is paramount in order to achieve cohesive quantum networks. In the first part of this thesis, we demonstrate this by generating a hybrid entangled resource between the two encodings and using it to teleport a dual-rail qubit onto its singlerail counterpart. Our key results yield an average fidelity of F = (92:8±2:2)% for the teleportation and F = (89:7 ± 2:1)% for entanglement swapping, thus confirming the applicability of this scheme towards a real-world implementation. This work completes the set of tools necessary for the interconversion between the three primary encodings of a qubit in the optical field: single-rail, dual-rail and continuous-variable. A remarkable aspect of quantum theory is that certain measurement outcomes are entirely unpredictable to all possible observers. Such quantum events can be harnessed to generate numbers whose randomness is asserted based upon the underlying physical processes. In the second part of this thesis, we formally introduce and experimentally demonstrate an ultrafast optical quantum randomness generator that uses a totally untrusted photonic source and whose idea we have patented. While considering completely general quantum attacks, we certify randomness at a rate of 1:1 Gbps with a rigorous security parameter of 10-20. Our security proof is entirely composable, thereby allowing the generated randomness to be utilised for arbitrary applications in cryptography and beyond.

It is well established now that light carries both spin and orbital angular momentum which are associated with circular polarisation and helical phase fronts. Orbital angular momentum degrees of freedom recently have been used frequently in quantum information processing as their states are described by vectors in a higher-dimensional Hilbert space which enhances the possibility of realising superior quantum information protocols. On the other hand, quantum coherence, which arises from the superposition principle, is a distinct feature of quantum mechanics that cannot be satisfactorily described by classical physics. Coherence is also identified as essential ingredient for applications of quantum information, computation, and quantum thermodynamics. Three research projects, with their related background information, are presented in this thesis. In the first one, we design a linear optical system to transform the maximally entangled state of a down-converted photon pair into a genuine entangled χ-type state, as this class of genuine entangled states has been showed to have many interesting entanglement properties and can be employed in several quantum information protocols. In the second project, we study the mechanism of angular momentum transfer from light to a dielectric medium when it undergoes total internal reflection. The result shows that the torque associated with angular momentum transfer appears shortly, when the light pulse hits the interface. Finally, we study quantum coherence transfer from a coherence resource initialised in a coherence state to an atomic state by the Jaynes-Cummings model, and we compare it to the coherent operation that uses a resource prepared in a ladder state described by Åberg's model. We found that a resource in a coherent state is more robust against failures.

Laser processing methods using excimer lasers have become very attractive for processing materials and the fabrication of micro and nano optical components. Diffraction gratings are used in a wide range of applications and require different fabrication methods. These components can be fabricated from a variety of biocompatible polymers. In this work, an Argon Fluoride (ArF) excimer laser operating at a wavelength of 193 nm has been used to process chitosan and agarose substrates. These materials have been characterised for differing laser processing conditions. Diffraction gratings and component demonstrators have been realised using Laser Direct writing (LDW) and nanoimprinting lithography (NIL). Characterisation of the ArF 193 nm laser work involves ablation threshold, optical absorption measurements and quantification of structural and morphological changes. This results can be used to identify the ideal laser fluence to be used for the production of a diffraction grating and similar optical components fabricated from chitosan. An ablation threshold of chitosan at 193 nm wavelength has been measured as 85 mJcm−2 and an optical absorption coefficient of 3×103 cm−1. A diffraction grating structure, measuring 12 μm, was generated in biocompatible materials films; chitosan and agarose, using a laser processing method. The results showed that the interaction between the laser and these materials can potentially open the pathway for a wide range of practical, real world applications such as optical and biomedical applications. Diffraction gratings with a feature size of 1 μm were successfully formed on the biocompatible material free standing films using a NIL technique. Microstructure cross grating patterning made of chitosan and agarose have been fabricated by ArF excimer laser processing using a mask projection ablation technique. Temperature rise calculations have been carried out by COMSOLTM Multi-Physics v5.3 using a Finite Element Method (FEM), to predict the temperature rise during laser ablation processing of chitosan and agarose. In addition, COMSOLTM Multi-physics v5.3 has been used to simulate the electric field in the vicinity of a diffraction grating that is illuminated with light from a HeNe laser emitting at a wavelength of 632.8 nm. The final experimental work investigated the possibility of realising 5CB liquid crystal doped chitosan diffraction gratings doped with Sudan Black B (SBB) dye to enhance the absorption properties at 632.8 nm. Diffraction gratings was fabricated using two intersecting beams from a HeNe laser. Polymer Dispersed Liquid Crystal (PDLC) chitosan doped with 5CB and SBB dye diffraction gratings were experimentally characterised.

Free space gradient force traps are hugely versatile experimental systems. Their realisation opens up new avenues for the exploration of various areas of fundamental physics, including both quantum physics and thermodynamics. Their high levels of sensitivity also have attractive implications for force sensing. In this thesis a novel experimental setup will be presented, along with experimental protocols, as a framework upon which such studies can be built. Using a paraboloidal mirror to create a diffraction limited, gradient force optical trap, the motion of nanoparticles ranging from 18 nm to 312 nm in diameter was detected via a single photodiode. Several properties of the levitated particles were measured, including: the mass, radius, oscillation amplitude (via the use of a volts to metre conversion factor) and the damping experienced at various pressures. This was done via two methods. The first, widely established, method required fitting a power spectral density, derived using the kinetic theory of gases, to the motion of the particle. The second, novel method, involved scanning the wavelength of the trapping laser. Using this method, it was possible to determine the mass of a levitated particle without assuming the kinetic model and material density. From the wavelength scan, the sensitivity of the experimental system was measured to be 200 fm/√Hz. Within this optical setup, the ability to control the trap frequencies of all three motional degrees of freedom, through varying the power of the trapping laser, was demonstrated. The ability to independently control and separate the transverse trapping frequencies from one another, as well as from the z axis, was also shown to be possible, using elliptically polarized light. The effect of changing the pressure inside the chamber in which a levitated nanoparticle is trapped is also explored. Trapping of nanoparticles at pressures as low as 10-5 mbar, without any active feedback, was achieved. A method for measuring the internal temperature of levitated particles was then demonstrated. This was done through measuring and fitting the Planck equation to the emitted thermal spectrum of a levitated silica nanoparticle. It was then shown that the temperature of levitated particles can be controlled via the intensity of the laser light as well as the pressure within the chamber. Over a pressure range of 1000 mbar to 0.04 mbar, an increase of temperature from 388 K to 480 K was measured. In the range of trapping laser intensities between 0.21 TW/m2 and 0.4 TW/m2, the resulting change ofa particle's temperature, from 367 K to 463 K, was observed. To control the centre of mass motion of levitated particles within the optical trap, parametric feedback cooling was implemented via modulation of the trap depth. Using this technique, the effect different feedback parameters have on particle motion was explored. The combination of optimizing the feedback parameters, alongside reducing the pressure, resulted in temperatures of Tz = 14 ±1 mK, Tx = 5 ±1 mK and Ty = 7 ±1 = mK. The observed Q factors on the order of 107 with predicted Q factors on the order of 1012 hold great promise for the realisation of ultrasensitive force detection. The system presented here has a force sensitivity on the order of 10-20 N pHz. Theoretical considerations show that, with some improvements to the experimental system, it would be possible to achieve centre of mass temperatures, and thus low phonon numbers, close to the quantum ground state. The second method to control the centre of mass motion of a levitated nanoparticle used squeezing pulses to classically squeeze its mechanical motion. This quadrature squeezing was achieved via non-adiabatic shifts of the nanoparticle's trap frequency and was carried out on a number of particles. The squeezing pulses implemented consisted of a rapid reduction in the trap frequency, followed by a brief period in time where the system was allowed to evolve, before the trapping frequency was rapidly returned to its original value. The effect of using single and multiple pulses to control this was explored and the optimal duration for a squeezing pulse characterized. For a single pulse, the maximum amount of squeezing was found to be λ = 3.2 ± 0.2 dB. To further increase the amount of squeezing applied to the levitated nanoparticle, a multiple pulse scheme was implemented. The effect of varying the time between pulses was investigated and the optimal time was found. The maximum amount of squeezing achieved in the system, occurred after 5 pulses, giving a squeezing factor of λ 9.4 ± 0.1 dB. The multiple pulse scheme was then applied to parametrically feedback cooled nanoparticles. The effect on the phase space, including its decay to a thermal state, after the application of squeezing pulses was characterized. The squeezing on parametricaly cooled particles. after the application of 5 pulses, was measured and the squeezing factor found to be λ = 8.4 ± 0.1 dB.

Direct UV-written silica-on-silicon provides an attractive platform for quantum optics, offering the key benets of low propagation losses and excellent optical fibre compatibility. This work has aimed to develop the necessary techniques and components for completely integrated quantum optics experiments to be carried out using this platform, on a larger scale than previously possible. Arrays of matched on-chip photon sources based on birefringence-matched spontaneous four-wave mixing (FWM) are demonstrated, both at 800 nm and in the telecommunications C-band, along with progress towards further integration of these sources. Thermo-optic phase shifters, for use in room temperature quantum circuits, have been optimised via modelling, and a range of alternative modulator technologies have been explored. Further work has been concerned with the development of a modular system for quantum optics, comprising a set of duplicate reconfigurable modules and the necessary drive electronics and software, with the intent of simplifying the task of identifying and quantifying manufacturing imperfections in large integrated experiments. Efforts have also been made to improve the detection efficiency of on-chip transition edge sensor (TES) single photon detectors, including the use of longer absorbers and high reflectors for multiple absorption passes; this has resulted in the demonstration of a photon-number-resolving detector with a Bragg grating enhanced quantum efficiency of 87%. Approaches for further increasing the detection efficiency are considered and a device for on-chip Hong-Ou-Mandel and photon subtraction experiments using these detectors is reported.

A proposal for performing quantum memory schemes with a light matter interface in Hollow Core Fibres is introduced. Various technical aspects of implementing such a scheme in the proposed interface are outlined and the different elements required to realize this scheme are discussed, primarily the detection of atomic levels and the extension of the scheme to magnetically trappable levels. A new method to dispersively measure populations and population difference of alkali atoms prepared in their two clock states is introduced, for future use in the Hollow Core Fibre interface. The method essentially detects the atom numbers based on the influence of the linear birefringence in the ensemble on the detection light beams via polarization homodyning. Sideband detection is performed after dressing the atoms with a radio-frequency field to circumvent low-frequency technical noises. The noise performance of this scheme is discussed along with design modifications aimed at reaching the atomic shot noise limit. Another technical aspect of realizing the quantum memory scheme in the proposed light-matter interface is the extension of the scheme to the trappable states of the atomic system as the atoms will be trapped in an atom chip magnetic field. We achieve this extension by showing the microwave spectroscopy of the ground state ensemble of radio-frequency dressed atoms which proves the existence of pseudo one-photon transitions between the trappable clock states. Finally, the preliminary designs and results of integrating an HCF in an atom chip experiment are discussed.

In this thesis, I have developed a range of theoretical and numerical techniques for modelling the behaviour of partially coherent optical systems and multi-mode detectors. The numerical simulations were carried out for the ultra-low-noise Transition Edge Sensors (TESs) being proposed for use on the SAFARI instrument on the cooled aperture infrared space telescope SPICA (34 - 210 μm). The optical behaviour of the SAFARI system is described in terms of the optical modes of the telescope, as distinct from the optical modes of the detector. The performance of the TESs were assessed in terms of signal power, background power and photon noise. To establish a method for precisely characterising and calibrating ultra-low-noise TESs, a cryogenic test system was designed and engineered to measure the optical efficiencies of the SAFARI TESs. The multi-mode, partially coherent illumination conditions of the measurement system were engineered to be precisely the same as those of the telescope. A major difference between the test system and the telescope’s optics is that the telescope will have focusing elements, but the test system was designed to avoid focusing elements in order to keep the optical path as clean as possible. The theoretical formalism and numerical models were adapted accordingly to address this difference. The numerical simulations show that the test system could provide near identical optical performance as that of the telescope system even though the focusing elements were absent. I also performed experimental measurements to investigate the optical efficiencies of the multi-mode TESs. The detectors worked exceedingly well in all respects with satisfactory optical efficiencies. In addition, it has been shown that the optical model provides a good description of the optical behaviour of the test system and detectors. Further modal analysis was developed to study losses in the multi-mode horns. The optical behaviour of the waveguide-mounted thin absorbing films in the far-infrared was modelled using a mode-matching method.

It is believed that the exotic properties of quantum systems can be harnessed to perform certain computational tasks more efficiently than classical theories allow. The production, manipulation and detection of single photons constitutes a potential platform for performing such non-classical information processing. The development of integrated quantum photonics has provided a miniaturised, monolithic architecture that is promising for the realisation of near-term analog quantum devices as well as full-scale universal quantum computers. In this thesis we investigate the viability of these photonic quantum computational approaches from an experimental and theoretical perspective. We implement the first universally reconfigurable linear optical network; a key capability for the rapid prototyping of photonic quantum protocols. We propose and demonstrate the use of these devices as a new platform for the programmable quantum simulation of molecular vibrational dynamics. We then tackle an important outstanding problem in linear optical quantum computing; quantifying how partial-distinguishability amongst photons aff ects logical error rates. Finally, we propose a series of schemes aimed at counteracting these distinguishability errors in order to achieve practical quantum technologies with imperfect photonic components.

The probing of the quantum nature of a macroscopic object is an open problem. Approaches in preparing quantum superposition towards a larger scale, which has been progressively accessible in a variety of experimental implementations, may detect new physics or extend the boundary of quantum theory. Development on a nano-mechanical system in the framework of quantum optics and information theory has opened new research directions. It paves ways to manipulate the wavefunction of a massive particle over a large spatial range and probe its quantum behavior to an unprecedented precision. In this thesis, quantum superposition on a mechanical system is studied theoretically in the light of possible implementations under current techniques in order to test superposition principle and the quantum nature of gravity in the mesoscopic region. The work includes two lines of study. In the first line, the motion of the center of mass (c.m.) of the mechanical system is coupled to its internal spin system magnetically, and a Ramsey scheme is developed based on coherent spin control. The wavepacket of the test object, under a spin-dependent force, may then be delocalized to a macroscopic scale. A gravity induced dynamical phase (accrued solely on the spin state, and measured through a Ramsey scheme) is used to reveal the above spatially delocalized superposition of the spin-nano-object composite system that arises during the scheme. A remarkable immunity to the motional noise in the c.m. (initially in a thermal state with moderate cooling) and also a dynamical decoupling nature of the scheme itself is revealed. A careful examination of the perturbation effect due to setup imperfection and environment-induced decoherence is performed, which shows that the Ramsey fringes have a high tolerance on those unwanted faults under realistic experimental conditions. The scheme also facilitates a gravimetry protocol that potentially could be developed for a novel on-chip gravimeter with a precision of $10^{-6}g/\sqrt{\text{Hz}}$. In the second line, an opto-mechanical experiment is proposed to entangle the motion of two mechanical oscillators through their mutual gravitational interaction. The feasibility of such an experiment is critically examined within the framework of cavity optomechanics. It is shown that within the decoherence time of mechanical noise and potentially gravitational induced state collapse, entanglement between mirrors could be obtained when the initial state of the cavity field is prepared in some particular states. Strategies that give enhancement to entanglement generation rate are studied in light of quantum estimation theory. It is shown that for a cavity initially in a coherent state, the resulting entanglement generation rate would be enhanced linearly with the amplitude of the coherent state. Lastly, it shows that in the proposed setup Casimir effect would significantly affect the gravity-induced entanglement. A proper shield can eliminate the detrimental effect of Casimir force, which, however, will constrain the closest distance between the mirrors in its implementation.

In the past decade, increasing demand and rapid developments in classical and quantum sciences resulted in advanced novel multipixel single photon detector arrays engineered on a single electronic chip. Silicon single photon avalanche detector (Si-SPAD) is one of the mainstream solution for low level light detection in visible and near-infrared wavelength region due to the dependable amplification of light signal. This thesis mainly focusses on three key experiments to showcase the potential applications of a single photon detector (Megaframe 32) consists of 32×32 square array Si-SPADs with picosecond timing circuits. With ≈ 50 ps timing resolution, each SPAD can perform time-correlated single photon counting independently. First, the concept of multiplexed single-mode wavelength-to-time mapping (WTM) of multimode light was investigated. The spacetime imaging capability of the Megaframe was then demonstrated by imaging the spatial modes emerging from a few-mode fibre enabling WTM of spatial modes. Finally, timeresolved discrete imaging in laser inscribed photonic lattices was demonstrated. By placing a photonic lattice in a linear cavity and re-injecting the output mode profile back to the lattice, the propagation of light was measured in quasi-real time manner. The experimental demonstrations using Megaframe will find applications in Raman spectroscopy, soliton imaging, quantum optics, and discrete waveguide optics.

Medical research and clinical diagnostics require imaging of large sample areas with sub-cellular resolution. Conventional imaging techniques can provide either high-resolution or wide field-of-view (FoV) but not both. This compromise is conventionally defeated by using a high NA objective with a small FoV and then mechanically scan the sample in order to acquire separate images of its different regions. By stitching these images together, a larger effective FoV is then obtained. This procedure, however, requires precise and expensive scanning stages and prolongs the acquisition time, thus rendering the observation of fast processes/phenomena impossible. A novel imaging configuration termed Multi-Aperture Fourier Ptychographic Microscopy (MA-FPM) is proposed here based on Fourier ptychography (FP), a technique to achieve wide-FoV and high-resolution using time-sequential synthesis of a high-NA coherent illumination. MA-FPM configuration utilises an array of objective lenses coupled with detectors to increase the bandwidth of the object spatial-frequencies captured in a single snapshot. This provides high-speed data-acquisition with wide FoV, high-resolution, long working distance and extended depth-of-field. In this work, a new reconstruction method based on Fresnel diffraction forward model was developed to extend FP reconstruction to the proposed MA-FPM technique. MA-FPM was validated experimentally by synthesis of a 3x3 lens array system from a translating objective-detector system. Additionally, a calibration procedure was also developed to register dissimilar images from multiple cameras and successfully implemented on the experimental data. A nine-fold improvement in captured data-bandwidth was demonstrated. Another experimental configuration was proposed using the Scheimpflug condition to correct for the aberrations present in the off-axis imaging systems. An experimental setup was built for this new configuration using 3D printed parts to minimise the cost. The design of this setup is discussed along with robustness analysis of the low-cost detectors used in this setup. A reconstruction model for the Scheimpflug configuration FP was developed and applied to the experimental data. Preliminary experimental results were found to be in agreement with this reconstruction model. Some artefacts were observed in these results due to the calibration errors in the experiment. These can be corrected by using the self-calibration algorithm proposed in the literature, which is left as a future work. Extensions to this work can include implementing multiplexed illumination for further increasing the data acquisition speed and diffraction tomography for imaging thick samples.

The process of image recording is arguably one of the most prevalent technology in modern society and continues to inspire vast swathes of research due to its widespread applications spanning military, medical and consumer spheres. The danger present in a field so broad is that separate niches of research can become isolated with critical advancements struggling to traverse the gulfs between. Unifying the field is the omnipresent drive to acquire an ever increasing quality of images at the lowest possible cost, a goal which warrants continual fundamental research. Quantum entanglement exhibits many intriguing characteristics which make it a suitable tool for such fundamental investigations. The process of spontaneous parametric down- conversion has offered a yet unbeaten strength of photon correlations with the quantum nature of their production providing a reliable and controllable source of single-photons. Arising from these attributes is the technique known as ghost imaging. Though now known to be classically possible, the strength of entanglement generated correlations is yet to be surpassed. This thesis implemented this technique in tandem with the cutting edge detector technology in order to probe the fundamentals of image formation. This form of imaging allowed us to subject an object to a known number of photons whilst acquiring structural information from spatially separate, correlated photons which never interact with the object. The strength of the produced correlations allow us to acquire low background, high resolution images with far less light than traditional techniques and affords many novel benefits. The possibility of incorporating this technique with pre-existent regimes allowed me to draw from advancements made across the landscape of imaging research. Although referred to as "quantum ghost imaging" throughout this work, it should be noted that the intrinsic quantum nature of the correlations was not directly relied upon but provided an ideal source of strongly correlated photons. In order to determine the limits of a traditional imaging system this thesis first sought to answer the question: "can an image of an object be reconstructed from fewer photons than ii pixels in the image?" In chapter 3 I approached this from the perspective of compression, which minimises redundant information within a signal. This lead to the development of an imaging regime capable of imaging with far fewer photons than pixels in the image. By employing assumptions about the sparsity of natural images I was able to reconstruct an image of a biological sample containing an average of less than one photon per image pixel. Having reduced the number of photons necessary to form an image I then considered alternative methods for reducing the optical energy impinging on a sample. I sought to answer the question: "can non-degenerate ghost imaging reduce the optical energy impinged upon an object during imaging". The photons produced in SPDC need not be of similar wavelengths, however may be chosen far from degeneracy, i.e. non-degenerate. In Chapter 4 I presented a ghost imaging system which illuminated the object with infrared light whilst recording the structural information via entangled visible photons. This allowed for objects opaque to visible light to be imaged in high quality without the need for a spatially resolving infrared detector, the state of the art of which lags behind their silicon based visible counterparts. I presented the systems capabilities by imaging objects which were etched into a gold substrate layered on to silicon, both of which are opaque to visible light. Not only did a reduction in energy deposition arise from the lower energy probe wavelength but applying the reconstruction techniques from the previous chapter brought that down to as low as ≈16 nJcm−2s−1. Seeking to expand the repertoire of applications, the low-light capabilities of my ghost imaging were applied to the technique of phase-contrast microscopy in chapter 5. Typically applied to translucent objects, phase-contrast imaging transfers phase information, i.e. the refractive index changed within the object, into an intensity distribution through the use of a phase-filter. In many of these applications the objects tend to be biological in nature, where high optical exposure can result in bleaching or damage. By applying the phase-filter non- locally, i.e. to the photons correlated to those probing the object, I acquired edge-enhanced images of a phase object whilst illuminating with significantly fewer photons than standard phase-contrast techniques. Having displayed the broad applicability of our low-light ghost imaging system, I then sought to determine the optical resolution in chapter 6. The resolution limits of ghost imaging are not clear at first glance owing to the resolutions dependence upon the strength of spatial correlations. As the length over which the spatial correlations are produced can be brought below the standard diffraction limit, it would seem the resolution of the system could be brought similarly low. To clarify this I artificially restricted the number of spatial modes in each of the correlated beams to uncover the physically realisable resolution. I show that although the resolution of a ghost imaging system to be fundamentally determined by the strength of the correlations, this can never be reached due to the inherent limitations of the intervening imaging system.

Quantum optics has successfully been used to test fundamental principles in quantum physics and to demonstrate the potential of quantum-enhanced technologies. Linear quantum optics, in which large quantum states of light are produced by optical interference of smaller quantum states, has proved to be particularly fruitful. Further progress will rely both on developing improved experimental tools to manipulate and measure quantum light, and on expanding and refining the range of applications of these technologies. This thesis presents our contributions towards both of these endeavours. We first focus on some of the components necessary for linear quantum optics, starting with the requirement for reconfigurable interference between several optical modes. We propose a novel design for interferometers that satisfy this requirement, which is based on a new mathematical decomposition of unitary matrices used to describe optical interference. We show that our design is more efficient than previously known designs. We also experimentally demonstrate a modular approach to building these devices, which is based on the assembly of multiple UV-written integrated photonic chips. These chips are characterised, and three of them are assembled into a structure shown to enable a wide range of optical transformations. We then study methods of photon detection, showing how photon detectors can be calibrated and discussing the operation of superconducting photon number resolving transition edge sensors. Next, we study two applications of linear optics. We examine the applicability of a proposal for simulating molecular spectroscopy using quantum optics in the presence of experimental imperfections. Our findings are illustrated with a proof of principle experiment in which we simulate part of the vibronic spectrum of the tropolone molecule. Finally, we study a class of optical devices, known as optical Ising machines, that has been shown to find solutions to difficult combinatorial problems. Describing the optical pulses in these devices in phase space as Gaussian quasi-probability distributions that evolve stochastically, we analyse the computational mechanism of these machines and show in theory that they can be simplified without affecting their performance.