No description available.

No description available.

There are a growing variety of research fields requiring non-contact micro- manipulation. An increasing number of these fields are turning to optical tweezers as a solution, owing to their high spatial and temporal resolution. Optical tweezers have the ability to quantitively exert and measure forces on the piconewton scale, a convenient force scale for soft biological materials, and are hugely versatile due to the wide assortment of beam shaping techniques that can be employed. The work in this thesis can be broadly divided into two main themes: that quantifying the optical trapping forces in shaped beams; and bringing control and simplification of complex systems to non-expert users who may utilise optical tweezers as part of interdisciplinary collaborations. Static beam shaping is used to generate a conically refracted optical trap and the trapping properties are characterised. It is shown that trapping in the lower Raman spot gives full, 3D gradient trapping, while the upper Raman spot allows for particle guiding due to its levitation properties. Particles in the Lloyd/Poggendorff rings experience a lower trap stiffness than particles in the lower Raman spot but benefit from rotational control. Dynamic beam shaping techniques are exploited for the simplification of complex systems through the development and testing of the HoloHands program. This software allows a holographic optical tweezers experiment to be controlled by gestures that are detected by a Microsoft Kinect. Multiple particle manipulation is demonstrated, as well as a calibration of the tweezers system. Application of trapping forces is demonstrated through an examination of integrin – ligand bond strength. Both wild type effector T cells and those with a kindlin-3 binding site mutation similar to that found in neutrophils from Leukocyte Adhesion Deficiency sufferers are investigated. Through the use of back focal plane interferometry, a bond rupture force of (17.9 ± 0.6) pN at a force loading rate of (30 ± 4) pN/s, was measured for single integrins expressed on wild type cells. As expected, a significant drop in rupture force of bonds was found for mutated cells, with a measured rupture force of (10.1 ± 0.9) pN at the same pulling rate. Therefore, kindlin-3 binding to the cytoplasmic tail of the β2-tail directly affects bond strength of single integrin-ligand bonds. An experimental system for studying these cells under more physiologically relevant conditions is also presented. Additionally, a low-cost optical micromanipulation system that makes use of simple microfabricated components coupled to a smartphone camera for imaging is proposed and demonstrated. Through the layering of hanging droplets of polydimethylsiloxane (PDMS) on microscope coverslips, lenses capable of optical trapping are created. Combination of PDMS with Sudan II dye led to the fabrication of long pass filters. An extension of this low-cost system into the life sciences is proposed through the adaptive use of bubble wrap, which allows for the culturing of cells in a chamber compatible with optical trapping.

Laser beams with precisely controlled intensity profiles are essential for many areas. We developed a beam shaping system based on the digital micromirror device (DMD) for ultra-cold atom experiments and other potential applications. The binary DMD pattern was first designed by the error diffusion algorithm based on an accurate measurement of the quasi-Gaussian incident beam from a real-world laser. The DMD pattern was projected to the image plane by a bandwidth-limited 4f telescope that converted this pattern to the grayscale image. The system bandwidth determined the theoretical limit of image precision by the digitization error. In addition, it controlled the spatial shape of the point spread function (PSF) that reflected the tradeoff between image precision and spatial resolution. PSF was used as a non-orthogonal basis set for iterative pattern refinement to seek the best possible system performance. This feedback process, along with stable performance of DMD, the blue-noise spectrum of the error diffusion algorithm, and low-pass filtering, guaranteed high-precision beam shaping performance. This system was used to produce various beam profiles for different spatial frequency spectra. First, we demonstrated high-precision slowly-varying intensity beam profiles with an unprecedented high intensity accuracy. For flattop and linearly-tilted flattop beams, we achieved 0.20-0.34% root-mean-square (RMS) error over the entire measurement region. Second, two-dimensional sinusoidal-flattop beams were used to evaluate image precision versus system bandwidth. System evaluation confirmed that this system was capable of producing any spatial pattern with <3% RMS error for the most system bandwidth. This experiment extended the beam shaping to any system bandwidth and provided a reference to estimate the output image quality based on its spatial spectrum. Later experiment using a Lena-flattop beam profile demonstrated the arbitrary beam profile generation. We implemented this system for applications on the homogenous optical lattice and dynamic optical trap generation. The DMD pattern was optimized by the iterative refinement process at the image feedback arm, and projected through a two-stage imaging system to form the desired beam profile at the working plane. Experiments demonstrated a high-precision beam shaping as well as a fast and dynamic control of the generated beam profile. / text

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Percussion drilling and trepanning are two laser drilling methods. Percussion drilling is accomplished by focusing the laser beam to approximately the required diameter of the hole, exposing the material to one or a series of laser pulses at the same spot to melt and vaporize the material. Drilling by trepanning involves cutting a hole by rotating a laser beam with an optical element or an x–y galvo-scanner. Optical trepanning is a new laser drilling method using an annular beam. The annular beams allow numerous irradiance profiles to supply laser energy to the workpiece and thus provide more flexibility in affecting the hole quality than a traditional circular laser beam. Heating depth is important for drilling application. Since there are no good ways to measure the temperature inside substrate during the drilling process, an analytical model for optical trepanning has been developed by considering an axisymmetric, transient heat conduction equation, and the evolutions of the melting temperature isotherm, which is referred to as the melt boundary in this study, are calculated to investigate the influences of the laser pulse shapes and intensity profiles on the hole geometry. This mathematical model provides a means of understanding the thermal effect of laser irradiation with different annular beam shapes. To take account of conduction in the solid, vaporization and convection due to the melt flow caused by an assist gas, an analytical two-dimensional model is developed for optical trepanning. The influences of pulse duration, laser pulse length, pulse repetition rate, intensity profiles and beam radius are investigated to examine their effects on the recast layer thickness, hole depth and taper. The ray tracing technique of geometrical optics is employed to design the necessary optics to transform a Gaussian laser beam into an annular beam of different intensity profiles. Such profiles include half Gaussian with maximum intensities at the inner and outer surfaces of the annulus, respectively, and full Gaussian with maximum intensity within the annulus. Two refractive arrangements have been presented in this study. Geometric optics, or ray optics, describes light propagation in terms of rays. However, it is a simplification of optics, and fails to account for many important optical effects such as diffraction and polarization. The diffractive behaviors of this optical trepanning system are stimulated and analyzed based on the Fresnel diffraction integral. Diffraction patterns of the resulting optical system are measured using a laser beam analyzer and compared with the theoretical results. Based on the theoretical and experimental results, the effects of experimental parameters are discussed. We have designed the annular beam shaping optical elements and the gas delivery system to construct an optical trepanning system. Laser drilling experiments are performed on the Stainless Steel-316 (SS 316) plate and the Inconel 718 (IN 718) plate. The geometry of the trepanning holes with different sizes is presented in this study.

No description available.

In remote areas without conventional cellular service, satellite communication is often the only viable option. Handheld devices for use with satellite communication networks require a high transmit power to obtain a reliable signal. The need for a high transmit power makes it difficult for the device to meet specific absorption rate (SAR) restrictions. An adaptive beam forming technique for shaping radiation away from the user’s head is proposed. This technique uses a back-to-back patch antenna design with an impedance monitoring based system capable of adaptively controlling the pattern of the antenna. The adaptive antenna system was designed, simulated, fabricated, and measured. The system could detect a head phantom within 3 cm of the antenna. SAR levels were verified to be within safety restrictions at 3 cm through simulation. By turning off the patch facing the user’s head when the phone is transmitting, and the user’s head is within 3 cm, it was shown that SAR levels could be reduced to safe levels. / February 2017

The generation of high-order harmonics opened an era of attosecond science wherein coherent light bursts are used to probe dynamic processes in matter with a time resolution short enough to resolve the motions of electrons. It enabled the development of extreme ultraviolet (XUV) and X-ray table-top sources with both temporal and spatial coherence, which provides the ability to shape the temporal and spatial structure of the XUV pulses. Scientists developed techniques to control and measure the temporal structure high harmonic emissions. These techniques exploited control of the driving laser pulse in the time domain and facilitated development of more advanced high-harmonic based XUV sources that have greatly impacted ultrafast measurements. In this thesis, I apply techniques to control and measure the spatial structure of high harmonic emissions, and discuss the underlying physics and potential applications of the interaction between spatially structured laser beams and materials. This study exploits the spatial degree of freedom in strong field interaction, which has not been given as much attention as the temporal degree of freedom. I use liquid crystal devices to shape the wave front of a fundamental laser beam to a vortex structure, then imprint this structured wave front onto XUV beams through high harmonic generation. This method provides an alternative to special XUV optics, which can manipulate the wave front of XUV radiation by all optical means. This result also reveals the conservation of orbital angular momentum in this extreme nonlinear wave mixing process. In addition to shaping the wave front, shaping the polarization of the driving beam also allows generation of circularly polarized the XUV radiation using a high harmonic source. This thesis also highlights the interplay between shaping the wave front and polarization in the high harmonic generation process. The topology of the structured beam can be maintained through this extreme nonlinear interaction due to the spin selection rules and spin-orbit conservation. Moreover, this thesis demonstrates an approach to integrate a vector beam into a broadband ultrafast light source and overcome the bandwidth limitation of mode converters. We use this approach to generate a few-cycle structured beam. In the future, this beam will be used to generate a strong ultrafast magnetic impulse in gas and solid targets by driving currents in a loop, which is a valuable tool for the future of magnetic metrology. The novel properties of structured laser beams discussed in this thesis expanded the capabilities of high harmonic based XUV sources and have opened a new field to explore this additional degree of freedom in strong field interactions.

Clinical wavefront-guided corneal ablation has been now the most technologically advanced method to reduce the dependence of glasses and contact lenses. It has the potential not only to eliminate spherocylindrical errors but also to reduce higher-order aberrations (HOA). Recent statistics show that more than 96% of the patients who received laser in situ keratomileusis (LASIK) treatment reported their satisfaction about the improvement on vision, six months after the surgery. However, there are still patients complaining that their vision performance did not achieve the expectation or was even worse than before surgery. The reasons causing the unexpected post-surgical outcome include undercorrection, overcorrection, induced HOA, and other postoperative diseases, most of which are caused by inaccurate ablation besides other pathological factors. Therefore, to find out the method to optimize the LASIK procedures and provide a higher surgical precision has become increasingly important. A proper method to calculate ablation profile and an effective way to control the laser beam size and shape are key aspects in this research to resolve the problem. Here in this Master of Philosophy degree thesis, the author has performed a meticulous study on the existing methods of ablation profile calculation and investigated the efficiency of wavefront only ablation by a computer simulation applying real patient data. Finally, the concept of a refractive surgery system with dynamical beam shaping function is sketched, which can theoretically overcome the disadvantages of traditional procedures with a finite laser beam size.