Untitled

Abstract

"Double-resonant extremely asymmetrical scattering of electromagnetic waves in periodic arrays separated by a gap", Optical and Quantum Electronics 33, 1-17 (2001) Two strong simultaneous resonances of scattering-double-resonant extremely asymmetrical scattering (DEAS)-are predicted in two parallel, oblique, periodic Bragg arrays separated by a gap, when the scattered wave propagates parallel to the arrays. One of these resonances is with respect to frequency (which is common to all types of Bragg scattering), and another is with respect to phase variation between the arrays. The diffractional divergence of the scattered wave is shown to be the main physical reason for DEAS in the considered structure. Although the arrays are separated, they are shown to interact by means of the diffractional divergence of the scattered wave across the gap from one array into the other. It is also shown that increasing separation between the two arrays results in a broader and weaker resonance with respect to phase shift. The analysis is based on a recently developed new approach allowing for the diffractional divergence of the scattered wave inside and outside the arrays. Physical interpretations of the predicted features of DEAS in separated arrays are also presented. Applicability conditions for the developed theory are derived.

Non-steady-state double-resonant extremely asymmetrical scattering of waves in periodic gratings

“…Each of these plane waves is regarded as an incident plane wave with the determined amplitude at the front grating boundary. Steady-state scattering of these waves is then analyzed by means of the rigorous [4,10] or approximate (if applicable) [1][2][3] theory of steady-state DEAS. The rigorous theory [4,10] is based on the enhanced T-matrix algorithm [11,12].…”

“…DEAS occurs in a non-uniform grating that consist of two strip-like joint [1,2,4] or separated [3] uniform gratings with different phases. It is characterised by a unique combination of two simultaneous resonances-one with respect to frequency, and the other with respect to phase shift between the gratings [1][2][3][4].…”

“…The second resonance with respect to phase shift between the joint or separated gratings is typical only for DEAS and results in a strong resonant maximum that occurs on the background of already resonantly large scattered wave amplitude (typical for EAS). The resonant phase shift is usually close to π, and the resultant scattered wave amplitudes may well exceed tens or hundreds of the amplitude of the incident wave at the front boundary [1][2][3][4]. It is important that not only the scattered wave amplitude, but also the amplitude of the incident wave (the 0th diffracted order) near the interface between the joint gratings, or in the gap between the two gratings experiences a strong resonant increase at the resonant phase shift [1][2][3][4].…”

“…The resonant phase shift is usually close to π, and the resultant scattered wave amplitudes may well exceed tens or hundreds of the amplitude of the incident wave at the front boundary [1][2][3][4]. It is important that not only the scattered wave amplitude, but also the amplitude of the incident wave (the 0th diffracted order) near the interface between the joint gratings, or in the gap between the two gratings experiences a strong resonant increase at the resonant phase shift [1][2][3][4]. It has also been demonstrated that strong DEAS occurs only in a grating of width that is smaller than a determined critical width [1,2].…”

“…Physically, half of the critical width was shown to equal the 1 distance within which the scattered wave can be spread across the grating by means of diffractional divergence, before being rescattered by the grating [1,2]. Thus, diffractional divergence of the scattered waves from one of the uniform gratings into another was shown to be one of the main physical reasons for DEAS [1][2][3]. Two simple methods for the determination of the critical width were suggested and justified [1,2].…”