Modal Analysis of Millimetre-wave and Terahertz Imaging Systems

This thesis presents the theory and applications of electromagnetic field calculation using orthogonal Gaussian beam modes within the context of far-infrared imaging systems. Laguerre and Hermite-Gaussian modes have been frequently reported in the analysis of paraxial millimetre-wave propagation in astronomical optical systems. Here the method of Gaussian beam mode analysis (GBMA) is extended to fields of optical research that have until recently been associated with wavelengths in the visible band. Using recently derived expressions for the non-paraxial diffraction of Hermite-Gaussian modes, the author demonstrates the modal calculation of far-field intensity distributions with less angular restriction on the accuracy of the method compared to the conventional paraxial description of orthogonal Gaussian modes. This method shows excellent agreement with predictions from more rigourous fullwave numerical methods such as the finite-difference time-domain algorithm, which is also described as a software tool in the modelling of horn and lens antennas. The properties of diffraction limited Bessel beams is described using the Laguerre-Gaussian expansion of conical lenses, and experimental measurements of a conical lens is presented to explore the validity of the use of these optical elements as horn coupled devices in millimetre wave imaging systems. A study of diffractive Fresnel lenses has been undertaken with a comparison of experimentally measured fields with those predicted by the modal techniques. The effects of such lenses on ultrashort paraxial pulses are also investigated using a novel numerical description of few-cycle fields as a superposition of pulsed Laguerre- Gaussian modes. The application of digital holography in the far-infra red band has the prospect of diffraction limited imaging systems without creating distortions and aberrations which is a common problem in conventional techniques using lenses and mirrors. The author presents results from a simple proof-of-concept system which exhibits the potential of this technique for application in, for example, mm-wave security imaging

Modal Analysis of Millimetre-wave and Terahertz Imaging Systems

This thesis presents the theory and applications of electromagnetic field calculation using orthogonal Gaussian beam modes within the context of far-infrared imaging systems. Laguerre and Hermite-Gaussian modes have been frequently reported in the analysis of paraxial millimetre-wave propagation in astronomical optical systems. Here the method of Gaussian beam mode analysis (GBMA) is extended to fields of optical research that have until recently been associated with wavelengths in the visible band. Using recently derived expressions for the non-paraxial diffraction of Hermite-Gaussian modes, the author demonstrates the modal calculation of far-field intensity distributions with less angular restriction on the accuracy of the method compared to the conventional paraxial description of orthogonal Gaussian modes. This method shows excellent agreement with predictions from more rigourous fullwave numerical methods such as the finite-difference time-domain algorithm, which is also described as a software tool in the modelling of horn and lens antennas. The properties of diffraction limited Bessel beams is described using the Laguerre-Gaussian expansion of conical lenses, and experimental measurements of a conical lens is presented to explore the validity of the use of these optical elements as horn coupled devices in millimetre wave imaging systems. A study of diffractive Fresnel lenses has been undertaken with a comparison of experimentally measured fields with those predicted by the modal techniques. The effects of such lenses on ultrashort paraxial pulses are also investigated using a novel numerical description of few-cycle fields as a superposition of pulsed Laguerre- Gaussian modes. The application of digital holography in the far-infra red band has the prospect of diffraction limited imaging systems without creating distortions and aberrations which is a common problem in conventional techniques using lenses and mirrors. The author presents results from a simple proof-of-concept system which exhibits the potential of this technique for application in, for example, mm-wave security imaging

Computational See-Through Near-Eye Displays

See-through near-eye displays with the form factor and field of view of eyeglasses are a natural choice for augmented reality systems: the non-encumbering size enables casual and extended use and large field of view enables general-purpose spatially registered applications. However, designing displays with these attributes is currently an open problem. Support for enhanced realism through mutual occlusion and the focal depth cues is also not found in eyeglasses-like displays. This dissertation provides a new strategy for eyeglasses-like displays that follows the principles of computational displays, devices that rely on software as a fundamental part of image formation. Such devices allow more hardware simplicity and flexibility, showing greater promise of meeting form factor and field of view goals while enhancing realism. This computational approach is realized in two novel and complementary see-through near-eye display designs. The first subtractive approach filters omnidirectional light through a set of optimized patterns displayed on a stack of spatial light modulators, reproducing a light field corresponding to in-focus imagery. The design is thin and scales to wide fields of view; see-through is achieved with transparent components placed directly in front of the eye. Preliminary support for focal cues and environment occlusion is also demonstrated. The second additive approach uses structured point light illumination to form an image with a minimal set of rays. Each of an array of defocused point light sources is modulated by a region of a spatial light modulator, essentially encoding an image in the focal blur. See-through is also achieved with transparent components and thin form factors and wide fields of view (>= 100 degrees) are demonstrated. The designs are examined in theoretical terms, in simulation, and through prototype hardware with public demonstrations. This analysis shows that the proposed computational near-eye display designs offer a significantly different set of trade-offs than conventional optical designs. Several challenges remain to make the designs practical, most notably addressing diffraction limits.Doctor of Philosoph

NASA SBIR abstracts of 1992, phase 1 projects

The objectives of 346 projects placed under contract by the Small Business Innovation Research (SBIR) program of the National Aeronautics and Space Administration (NASA) are described. These projects were selected competitively from among proposals submitted to NASA in response to the 1992 SBIR Program Solicitation. The basic document consists of edited, non-proprietary abstracts of the winning proposals submitted by small businesses. The abstracts are presented under the 15 technical topics within which Phase 1 proposals were solicited. Each project was assigned a sequential identifying number from 001 to 346, in order of its appearance in the body of the report. Appendixes to provide additional information about the SBIR program and permit cross-reference of the 1992 Phase 1 projects by company name, location by state, principal investigator, NASA Field Center responsible for management of each project, and NASA contract number are included

LASER Tech Briefs, Spring 1994

Topics in this Laser Tech Brief include: Electronic Components and Circuits. Electronic Systems, Physical Sciences, Materials, Mechanics, Fabrication Technology, and books and reports