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The invention of optical tweezers almost forty years ago has triggered applications spanning multiple disciplines and has also found its way into commercial products. A major breakthrough came with the invention of holographic optical tweezers (HOTs), allowing simultaneous manipulation of many particles, traditionally done with arrays of scalar beams. Here we demonstrate a vector HOT with arrays of digitally controlled Higher-Order Poincaré Sphere (HOPS) beams. We employ a simple set-up using a spatial light modulator and show that each beam in the array can be manipulated independently and set to an arbitrary HOPS state, including replicating traditional scalar beam HOTs. We demonstrate trapping and tweezing with customized arrays of HOPS beams comprising scalar orbital angular momentum and cylindrical vector beams, including radially and azimuthally polarized beams simultaneously in the same trap. Our approach is general enough to be easily extended to arbitrary vector beams, could be implemented with fast refresh rates and will be of interest to the structured light and optical manipulation communities alike.

The work presented in this thesis focuses on the creation of customised structured light beams, their analysis, characterisation and application in optical trapping and tweezers.In the first Chapter, we start by presenting an over-view of the thesis as well as a review of literature on laser beam shaping and its applications in optical tweezers. A theoretical description and de nitions of customised laser modes utilised in this thesis such as LG and HG beams are presented in Chapter 2. Concepts on digital laser beam shaping techniques to realise customised structured light elds are described in Chapter 3. Two methods of generating customized laser modes namely complex amplitude modulation and phase only modulation are considered. Based on the ability of the SLM to create multiple beams simultaneously, the multiplexing concept is also discussed. Following the same line, a new approach to obtain multiple vector beams on a single hologram is presented. In addition, an approach to create shape invariant vector at-top beams is discussed. Since we are also interested in the application of these custom light elds in optical tweezers, we discuss the fundamentals of optical trapping in Chapter 4.Experimental realisation of LG and HG beams is then presented in Chapter 5. With the use of the beam shaping methods in Chapter 3, we demonstrate light beam shaping and multiplexing. In addition, a quantitative analysis to determine the multiplexing properties of SLMs as well as an investigation on the maximum number of beams that can be multiplexed is presented.A novel experimental method that enables the simultaneous generation of many vector beams using a single digital hologram is described in Chapter 6. This method is interferometric in nature and relies on the multiplexing concept. We demonstrate the simultaneous generation of multiple vector vortex beams each with various polarization distributions. The exibility of our approach is further con rmed through the creation of multiple vector Bessel beams.Finally in Chapter 7, we present the application of our structured light elds in an optical trapping and tweezers system. The vector at-top beam is rstly considered where a new holistic classical and quantum toolkit to analyse this beam during propagation is presented. The experimental realisation of such beams which exploits the polarisation dependent e ciency of spatial light modulators is described. We then demonstrate the versatility of our vector at-top beam in an optical trapping and tweezing application. Following the experimental generation of multiple vector beams in Chapter 6, a novel vector holographic optical trap with arrays of digitally controlled Higher-Order Poincar e Sphere (HOPS) beams is also presented. We employ a simple set-up using a spatial light modulator and show that each beam in the array can be manipulated independently and set to an arbitrary HOPS state, including replicating traditional scalar beam HOTs. We demonstrate trapping and tweezing with customized arrays of HOPS beams comprising scalar orbital angular momentum and cylindrical vector beams, including radially and azimuthally polarized beams simultaneously in the same trap. Our approach is general enough to be easily extended to arbitrary vector beams.

Zinc oxide (ZnO) continues to receive widespread attention due to its excellent optical and electronic properties; it demonstrates the combined characteristics of high transmittance and electrical conductivity. Despite the tremendous drive for its application in optoelectronic devices, the full nature of the point defects and defect complexes have not been characterised comprehensively. In this work, luminescence characteristics of the intrinsic defects in ZnO thin films and the rare-earth ions Eu3+and Tb3+in ZnO powders are investigated under blue-laser excitation.The thin films used in this study were deposited using the radio-frequency magnetron sputtering method over a 2 hour duration under varied power and substrate bias conditions. The powders were synthesized by the chemical bath deposition method with dopant concentrations of 1.0 mol%. Grazing incidence X-ray diffraction (XRD) was used to determine the lattice properties of the samples. Photoluminescence studies were primarily conducted at room temperature (300 K) with the 457.9 nm, 476.5 nm and 488.0 nm laser lines as excitation sources.For the ZnO thin films, XRD patterns of a hexagonal wurtzite structure with a c/aratio of about 1.60 and a u-parameter of 0.38 were obtained. Photoluminescence measurements show a broad emission band in the 500.0-900.0 nm range, centred at 656.0 nm. Annealed films yielded relatively more intense photoluminescence spectra than the as-prepared films. The intrinsic point defects and defect level transitions responsible for the broad emission are discussed.For the ZnO powders, the XRD patterns of the annealed samples of pristine ZnO, ZnO:Eu3+and ZnO:Tb3+are similarly consistent with a hexagonal wurtzite ZnO phase. Energy dispersive spectroscopy (EDS) confirmed the presence of the Eu3+and Tb3+dopants in the respective ZnO host while scanning electron microscopy (SEM) measurements showed the morphology of the sample powders. Photoluminescence spectra of pelletized samples, obtained in the 460.0-900.0 nm range, exhibit relatively intense Eu3+and Tb3+emission bands superimposed on a broad emission background. The RE3+emission bands are attributed to the 5D0→ 7FJ (J = 0, 1, 2, 3, 4) and the 5D4→ 7FJ (J = 0, 1, 2, 3, 4, 5, 6) electronic transitions of Eu3+and Tb3+, respectively, while the background emission is attributed to intrinsic defects. Crystal-field energy levels for the Eu3+ion and the Tb3+ion occupying a C3v symmetry site were deduced from fitting Gaussian curves to the RE3+emission bands. Possible channels for transfer of energy from the intrinsic defects to Eu3+and Tb3+are discussed.

Complex vector light fields, classically entangled in polarization and phase, have become ubiquitous in a wide variety of research fields. This has triggered the demonstration of a wide variety of generation techniques. Of particular relevance are those based on computer-controlled devices due to their great flexibility. More specifically, spatial light modulators have demonstrated that almost any vector beam, with various spatial profiles and polarization distributions can be generated. Crucially, none of these techniques has proven capable to generate multiple vector beams simultaneously. Here, we put forward a novel technique that exploits the superposition principle in optics to enable the simultaneous generation of many vector beams using a single digital hologram. As proof-of-principle, we demonstrated the simultaneous generation of twenty vector vortex beams with various polarization distributions and spatial shapes on a single SLM, each of which with their own spatial shape and polarization distribution.

The on-demand tailoring of light's spatial shape is of great relevance in a wide variety of research areas. Computer-controlled devices, such as Spatial Light Modulators (SLMs) or Digital Micromirror Devices (DMDs), offer a very accurate, flexible and fast holographic means to this end. Remarkably, digital holography affords the simultaneous generation of multiple beams (multiplexing), a tool with numerous applications in many fields. Here, we provide a self-contained tutorial on light beam multiplexing. Through the use of several examples, the readers will be guided step by step in the process of light beam shaping and multiplexing. Additionally, on the multiplexing capabilities of SLMs to provide a quantitative analysis on the maximum number of beams that can be multiplexed on a single SLM, showing approximately 200 modes on a single hologram.