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Extremely asymmetrical scattering of waves in periodic Bragg arrays

Pile, David Fujio Pelleas (2003) Extremely asymmetrical scattering of waves in periodic Bragg arrays. PhD thesis, Queensland University of Technology.


This thesis fills in the gaps in the existing theory of wave phenomena in thick diffraction gratings at extreme angles of scattering, i.e. when the scattered wave propagates parallel or almost parallel to the grating boundaries. A consistent theory of a new type of Bragg scattering of bulk and guided optical modes in thick uniform and non-uniform, dissipative and non-dissipative, slanted periodic gratings has been developed. This type of scattering is

called extremely asymmetrical scattering (EAS).

One of the main distinctive features of EAS is the strong resonant increase of the scattered wave amplitude compared to the amplitude of the incident wave. Several unique combinations of strong resonances shaping a complex multi-resonant pattern of EAS in different types of gratings have been predicted and investigated theoretically and numerically. This includes the prediction of a new resonant wave effect in non-uniform gratings with varying phase – double-resonant EAS, the discovery of several sharp and strong resonances with respect to scattering angle in gratings with the scattered wave

propagating almost parallel to the grating boundaries (grazing-angle scattering (GAS)) for the case of second-order scattering, and the prediction of a new type of eigenmode in gratings with second-order scattering (especially in gratings with large amplitude). In addition, several other important practical problems that may be crucial for the experimental observation and application of EAS and GAS have been solved. These are the determination of the tolerance of EAS to small grating imperfections, e.g., fluctuations of the grating amplitude, prediction

of unusually high sensitivity of second-order EAS to small variations of mean structural parameters, determination of the effect of weak dissipation on EAS, etc. Physical reasons for the predicted resonances and effects are explained. In particular, the crucial role of the diffractional divergence for EAS and GAS has been revealed, especially for non-uniform gratings.

Methods of analysis involve the approximate and rigorous approaches. The approximate method is based on understanding the role of the diffractional divergence in the geometry of EAS and the two-wave approximation (valid for any types of waves). The rigorous approach is based on the rigorous coupled-wave analysis (RCWA) and, in particular, the known enhanced T-matrix

algorithm (by Moharam, et al.) that is numerically stable for narrow and wide gratings with arbitrary amplitude (valid only for bulk electromagnetic waves).

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ID Code: 15794
Item Type: QUT Thesis (PhD)
Supervisor: Gramotnev, Dmitri, Milburn, Gerard, & Quintarelli, Frank
Keywords: Bragg scattering, coupled-wave analysis, diffraction, diffractional divergence, diffraction grating, diffractive optics, electromagnetic waves, extremely asymmetrical scattering, Fourier analysis, grating, grazing-angle scattering, guided waves, guided modes, non-uniform periodic gratings, optics, physical optics, periodic array, physics, rigorous coupled-wave analysis, scattering
Department: Science
Institution: Queensland University of Technology
Copyright Owner: Copyright David Fujio Pelleas Pile
Deposited On: 03 Dec 2008 13:49
Last Modified: 29 Oct 2011 05:38

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