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The amalgamation of the technologies of Microfabrication and Rapid Prototyping and Manufacturing is a field that has witnessed a surge of research activity in recent years. This thesis demonstrates the development of a novel microfabrication system characterised by the use of Computer Generated Holograms (CGHs) as part of a StereoLithographic rapid prototyping system in cohesion with applied microfabrication techniques. CGHs are reconstructed using a laser diode operating at a visible wavelength (407nm) and subsequently implemented in the fabrication of a microstructure. The hologram encoding method utilized two-pixel macropixels implemented on a smectic, analogue ferroelectric liquid crystal (AFLC) spatial light modulator (SLM). This, in conjunction with the bipolar nature of the modulating device, allows for full complex optical modulation. A commercial photopolymer is chosen as the target material. The underlying chemical processes comprising its photochemical behaviour in its native state, as well as in the presence of sensitizers or visible light photoinitiators, are described and the suitability of each to the StereoLithographic processes evaluated. Experimental determination of the effect of such holograms on the target material is undertaken, which include nondegenerate four wave mixing to investigate optical characteristics and cure depth measurement techniques to evaluate photochemical response. The beneficial effects of using a visible light source with respect to the final physical properties of the component are determined. Final product microstructures displaying a variety of topologies are experimentally realised, accompanied by descriptions of their respective fabrication techniques and formulation requirements

The rate at which new communications technologies are being developed has been immense and will continue to intensify for the foreseeable future. This evolution is fuelled by the desire to meet the wants and needs of the global community, by developing devices able to offer ever-increasing functionality, with greater complexity. To achieve this designers are forced to move to higher and higher frequencies. The antenna, as one of the fundamental building blocks of any radiated wave system, and as such, must develop along with the evolution of the communication system be it for, mobile, satellite or point to point systems. Antenna designers need to be able to test antenna, to ensure they exhibit the characteristics to which they were designed. Antenna test becomes progressively more difficult and costly as both, the operating frequency and the size of the antenna increase, especially for the measurement of the antenna Far-Field radiation pattern. Either the distance over which the measurement must be made becomes unfeasibly large or expensive measurement equipment is required to attain the phase component of the antenna field, where traditional methods for measuring close to the antenna are applied. Techniques have been developed to eliminate the need for the expensive phase measurement at reduced distances. Specifically of interest in this thesis, is the optical process of Off-Axis holography. The process allows phase information to be retained in a scalar measurement by use of a phase coherent known reference source. The reference desired reference source is a plane wave, which although possible at optical frequencies with the use of lasers is problematic at microwave frequencies. To date the plane wave characteristic required has been approximated using conventional radiating elements, which degrades the quality of the recorded holographic image. This thesis proposes a novel implementation of the Off-Axis hologram system, for application in the microwave frequency region. The novel system developed here addresses the problem of generating the desired plane wave characteristic. The conventional radiating element used to provide the near plane wave reference is replaced by a synthetic equivalent, which allows the magnitude and phase of the reference beam to be directly controlled at every measurement location required. Practical verification of the novel system proposed has been performed, with comparisons made between the results obtained from the novel technique and standard techniques used in industry. The comparisons show that the novel implementation is valid and able to provide good repeatable results.

Digital holography is a new technology emerged in 1994. Because of developments of Laser, personal computer, and CCD sensor, digital holography is finding a remarkably wide range for applications. The reconstruction algorithm is the corner stone of digital holography. It simulates and models the optical reconstruction process with numerical algorithms. A number of reconstruction algorithms have been developed for digital holography in recent years, for instance, the digital implementations of the Fresnel transform, the Fraunhofer transform, and Wavelet transform. We examined all above reconstruction algorithms and developed our own variants of Angular Spectrum and Wavelet/Chirplet reconstruction algorithms. Further to these reconstruction algorithms, we developed miscellaneous algorithms to make digital holography more sophisticated. To detect the focus of an individual hologram, auto-focusing algorithms are developed. To break the resolution limitation introduced by the CCD sensor we present digital in-line holography illuminated by divergent light and corresponding reconstruction algorithms. To expand digital holography in a wider range of common applications, digital video holography is exploited. The holographic video can be reconstructed in both z and time axes. We integrated all the algorithms into software for holographic recording and processing electronically. We also applied the digital holography in a real biological application, sediment erosion study.

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No description available.

Holographic lithography is a new technique developed for the fabrication of threedimensional photonic crystals in polymer. Four coherent laser beams are interfered to generate a three-dimensionally periodic interference pattern in a film of photoresist. Subsequent processing steps render a three-dimensional photonic crystal, whose structure is commensurate with the original interference pattern. Two interference patterns are discussed in detail: a face-centred cubic pattern with a conventional lattice constant of 922nm in air and a face-centred cubic pattern with a conventional cube side of 397nm in air (interference wavelength 355nm). Three types of basis are presented for the interference pattern with a 922nm lattice constant: a righthanded, a left-handed and a non-chiral basis. Photonic crystals have been fabricated with both a chiral and a non-chiral basis and evaluated by scanning electron microscopy. Optical transmission measurements are presented for the non-chiral photonic crystals and are interpreted in both a Bragg scattering model and a photonic bandstructure model. A 'GaAs' and a 'diamond' basis are presented for the interference pattern with a 397nm lattice constant. Photonic crystals have been fabricated with the 'GaAs' basis and evaluated by scanning electron microscopy.

Digital holography is a technique for the recording of holograms via CCD/CMOS devices and enables their subsequent numerical reconstruction within computers, thus avoiding the photographic processes that are used in optical holography. This thesis investigates the various techniques which have been developed for digital holography. It develops and successfully demonstrates a number of refinements and additions in order to enhance the performance of the method and extend its applicability. The thesis contributes to both the experimental and numerical analysis aspects of digital holography. Regarding experimental work: the thesis includes a comprehensive review and critique of the experimental arrangements used by other workers and actually implements and investigates a number of these in order to compare performance. Enhancements to these existing methods are proposed, and new methods developed, aimed at addressing some of the perceived short-comings of the method. Regarding the experimental aspects, the thesis specifically develops:• Super-resolution methods, introduced in order to restore the spatial frequencies that are lost or degraded during the hologram recording process, a problem which is caused by the limited resolution of CCD/CMOS devices.• Arrangements for combating problems in digital holography such as: dominance of the zero order term, the twin image problem and excessive speckle noise.• Fibre-based systems linked to tunable lasers, including a comprehensive analysis of the effects of: signal attenuation, noise and laser instability within such systems.• Two-source arrangements for contouring, including investigating the limitations on achievable accuracy with such systems. Regarding the numerical processing, the thesis focuses on three main areas. Firstly, the numerical calculation of the Fresnel-Kirchhoff integral, which is of vital importance in performing the numerical reconstruction of digital holograms. The Fresnel approximation and the convolution approach are the two most common methods used to perform numerical reconstruction. The results produced by these two methods for both simulated holograms and real holograms, created using our experimental systems, are presented and discussed. Secondly, the problems of the zero order term, twin image and speckle noise are tackled from a numerical processing point of view, complementing the experimental attack on these problems. A digital filtering method is proposed for use with reflective macroscopic objects, in order to suppress both the zero-order term and the twin image. Thirdly, for the two-source contouring technique, the following issues have been discussed and thoroughly analysed: the effects of the linear factor, the use of noise reduction filters, different phase unwrapping algorithms, the application of the super-resolution method, and errors in the illumination angle. Practical 3D measurement of a real object, of known geometry, is used as a benchmark for the accuracy improvements achievable via the use of these digital signal processing techniques within the numerical reconstruction stage. The thesis closes by seeking to draw practical conclusions from both the experimental and numerical aspects of the investigation, which it is hoped will be of value to those aiming to use digital holography as a metrology tool.