<p>We calculate electromagnetic transmission through periodic gratings using a mode-matching method for solving Maxwell's equations. We record the derivation of the equations involved for several variations of the problem, including one- and two- dimensionally periodic films, one-sided films, films with complicated periodicity, and a simpler formula for the case of a single contributing waveguide mode. We demonstrate the effects of the Rayleigh anomaly, which causes energy transmission to be very low compared to nearby frequencies, and the associated transmission maxima which may be as high as 100% for certain energy frequencies. Finally we present further variations of the model to account for the effects of conductivity, finite hole arrays, and collimation. We find that assuming the film is perfectly conducting with infinite periodicity does not change the transmission sufficiently to explain the difference between experimental and theoretical results. However, removing the assumption that the incident radiation is in the form of a plane wave brings the transmission much more in agreement with experimental results.</p> / Dissertation

Thesis (Ph. D.)--School of Electrical and Computer Engineering, Georgia Institute of Technology, 2004. Directed by Elias N. Glytsis. / Vita. Includes bibliographical references (leaves 179-190).

Thesis (M.S.)--Brigham Young University. Dept. of Electrical and Computer Engineering, 2003. / Includes bibliographical references (p. 183-193).

This thesis details original experimental investigations in to the interaction of light with the mobile electrons at the surface of metallic diffraction gratings. The gratings used in this work to support the resultant trapped surface waves (surface plasmon polaritons), may be divided into two classes: ‘crossed’ bigratings and ‘zigzag’ gratings. Crossed bigratings are composed of two diffraction gratings formed of periodic grooves in a metal surface, which are crossed at an angle relative to one another. While crossed bigratings have been studied previously, this work focuses on symmetries which have received comparatively little attention in the literature. The gratings explored in this work possesses two different underlying Bravais lattices: rectangular and oblique. Control over the surface plasmon polariton (SPP) dispersion on a rectangular bigrating is demonstrated by the deepening of one of the two constituent gratings. The resulting change in the diffraction efficiency of the surface waves leads to large SPP band-gaps in one direction across the grating, leaving the SPP propagation in the orthogonal direction largely unperturbed. This provides a mechanism to design surfaces that support highly anisotropic propagation of SPPs. SPPs on the oblique grating are found to mediate polarisation conversion of the incident light field. Additionally, the SPP band-gaps that form on such a surface are shown to not necessarily occur at the Brillouin Zone boundaries of this lattice, as the BZ boundary for an oblique lattice is not a continuous contour of high-symmetry points. The second class of diffraction grating investigated in this thesis is the new zigzag grating geometry. This grating is formed of sub-wavelength (non-diffracting) grooves that are ‘zigzagged’ along their length to provide a diffractive periodicity for visible frequency radiation. The excitation and propagation of SPPs on such gratings is investigated and found to be highly polarisation selective. The first type of zigzag grating investigated possesses a single mirror plane. SPP excitation to found to be dependant on which diffracted order of SPP is under polarised illumination. The formation of SPP band-gaps is also investigated, finding that the band-gap at the first Brillouin Zone boundary is forbidden by the grating’s symmetry. The final grating considered is a zigzag grating which possesses no mirror symmetry. Using this grating, it is demonstrated that any polarisation of incident light may resonantly drive the same SPP modes. SPP propagation on this grating is found to be forbidden in all directions for a range of frequencies, forming a full SPP band-gap.

Many applications in optical research require the use of diffraction limited point images with reduced spot sizes. The instrumentation that evaluates these small diameter images must have high resolution (sub-micron) capabilities. One method used to measure sub-micron optical point images is a scanning grating technique. However, many characteristics of this measurement technique have not been fully examined. In this paper, the sensitivity of this measurement technique to the scanning mechanism, beam characteristics, and grating tilt is evaluated.

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Sensitivity to differential motion components, shearing and compressive (opposed) motion, was examined. The hypothesis that the visual system contains local mechanisms specifically sensitive to these types of motion was tested. Stimuli consisted of two moving sinusoidal gratings. Sensitivity to shear and compression was compared with sensitivity for linear motion. Lower thresholds of motion and contrast sensitivities were obtained. Subjects were more sensitive to opposed than to non-opposed motion for a range of grating orientations and different grating spatial frequencies. However sensitivity for opposed motion decreased in the presence of a second added linear motion. The hypothesis of local shear and compression mechanisms was rejected in favour of antagonistic (opponent) interactions between local motion mechanisms. Motion capture was examined. Stimuli were made up of a circular test grating surrounded by another grating. Subjects were required to judge the direction of motion of the test grating. Experiments examined the effects on motion capture of: centre grating size; orientation of surround; relative contrast of centre and surround; plaids in the surround. Conditions favouring motion capture were: with the smallest centre grating; with surround and centre orientations within thirty degrees; with surround had higher contrast than the centre; and only when a plaid surround contained a component of similar orientation as the centre. For conditions of motion capture relative to those of no-capture, increased velocity thresholds for judging the centre direction were found. This was associated with a shift in the bias point between opposed directions with no change in overall sensitivity to motion. It is suggested that a cooperative network of local motion mechanisms featuring centre-surround opponency can account for all the results of this study.

This thesis reports the research and industry-related works carried out from the development of a fibre-optic strain sensor system for Civil Engineering applications. A sensor system consists of a number of core components, including the sensing element, interrogation/demodulation, multiplexing, signal processing and hardware equipment. In the process of development, a number of issues have been identified and investigated, which resulted in the improvement of the system performance, as well as the proposal of new techniques for the sensor system. First, an improved demodulation technique for a type of sensor, namely the fibre Fizeau interferometer (FFI), is presented. The technique is based on the improvement of the Fourier transform peak detection method, which suffers severely from the poor resolution and accuracy of finding the sensor cavity length. The improvement over the original method has been compared and verified through simulations and experiments. Second, a simultaneous demodulation technique for multiplexed FFI and fibre Bragg grating (FBG) sensors using the discrete wavelet transform (DWT) is proposed. Third, a multiplexing technique using amplitude-modulated chirped FBGs and the DWT is proposed. These two proposed techniques have been demonstrated experimentally through strain measurements. The strain resolution, crosstalk and limitations are investigated. In addition, simultaneous quasi-static strain and temperature sensing of different metal plates are performed. Fibre-optic sensors have found numerous applications in different areas. In this thesis, the use of FBG sensors in Civil Engineering applications is demonstrated in four experimental studies, including: (i) long-term measurement of drying shrinkage and creep of structural grade concrete; (ii) simultaneous measurement of shrinkage and temperature of reactive powder concrete (RPC) at early-age; (iii) measurement of coefficients of thermal expansion of cement mortar and RPC; and (iv) field-trial on the strain monitoring of the world?s first RPC road bridge. In addition, the experimental and practical issues of using FBG sensors are considered.

Thesis (MS )--Montana State University--Bozeman, 2008. / Typescript. Chairperson, Graduate Committee: Douglas S. Cairns. Includes bibliographical references (leaves 142-147).