Arthur R. McGurn

Antiferromagnetic-spin-flop critical field in MnxZn1-xF2

The antiferromagnetic resonance in MnxZn1-xF2, measured recently by Wiltshire (1977), gives information about the antiferromagnetic-spin-flop critical field Hc(x). The authors calculate Hc(x) on the basis of known exchange and anisotropy parameters of the MnF2 system. The concentration dependence of the anisotropy is determined through a separation between short-range and long-range parts of the dipolar forces while the Mn-Mn exchange interactions are assumed to be unaffected by the zinc dilution. The theoretical treatment is based on an extension of the Izyumov type of perturbation theory (1966) to non-magnetic impurity problems. Coherent potential approximation (CPA) analyses are also carried out. Results are in reasonable agreement with experiment.

Localization effects in the elastic scattering of light from a randomly rough surface

The diffuse scattering of light from a randomly rough surface is calculated for the case in which this scattering is accompanied by the resonant excitation of surface polaritons. In these calculations the light is incident normally upon the plane of the mean surface. The diffuse scattering is shown to exhibit intensity maxima in the antispecular direction, owing to the localization of surface polaritons. These maxima are smaller for s to s, s to p, and p to s scattering than for p to p scattering. Two calculations are presented: one in which dielectric losses are large compared with the attenuation of surface polaritons that is due to the roughness and one in which dielectric losses are small compared with other mechanisms of attenuation. Both calculations proceed by diagrammatic expansions that take into account the diagrams responsible for localization phenomena. The surface roughness is considered to be weak enough that such perturbation techniques are applicable.

Photonic band structure of a truncated, two-dimensional, periodic dielectric medium

We calculate the photonic band structure for the propagation of electromagnetic waves through a structure that consists of parallel, identical, dielectric rods of finite length, whose intersections with a perpendicular plane form a two-dimensional crystal. The rods are embedded in a medium with a different dielectric constant, and the composite system is confined between a pair of perfectly conducting plates that are perpendicular to the rods. The electromagnetic waves propagate in a plane perpendicular to the rods. The resulting photonic band structure can display absolute band gaps if the separation between the perfectly conducting plates is sufficiently large or sufficiently small.

Experimental study of the opposition effect in the scattering of light from a randomly rough metal surface

The opposition effect manifested as a narrow peak in the angular distribution of the intensity of diffusely scattered light in the backward (antispecular or retroreflection) direction has been experimentally investigated. A monostatic bidirectional laser reflectometer was used to measure the opposition effect of copper and gold surfaces under illumination at 0.6328 microm. The results are compared with a recent theory of the elastic scattering of light from a randomly rough metal surface that predicts such a peak in the retroreflectance direction, which, in certain conditions, can be related to the localization of surface polaritons.

An analogue of enhanced backscattering in the transmission of light through a thin film with a randomly rough surface

Abstract We study theoretically the transmission of p-polarized light through a thin metal film, one of whose surfaces is randomly rough. It is found that the angular distribution of the intensity of the diffuse component of the transmitted light has a narrow peak at an angle of transmission that corresponds to the antispecular direction. This peak is the analogue for transmission of the enhanced backscattering of p-polarized light from a randomly rough metal surface.

Enhanced transmission due to disorder.

The transmissivity of a one-dimensional random system that is periodic on average is studied. It is shown that the transmission coefficient for frequencies corresponding to a gap in the band structure of the average periodic system increases with increasing disorder while the disorder is weak enough. This property is shown to be universal, independent of the type of fluctuations causing the randomness. In the case of strong disorder the transmission coefficient for frequencies in allowed bands is found to be a non monotonic function of the strength of the disorder. An explanation for the latter behavior is provided.

Intrinsic localized modes in nonlinear photonic crystal waveguides

Abstract A discussion is given of the theory of intrinsic localized modes (ILM) for nonlinear waveguide impurities in photonic crystals. Conditions are determined for the existence of both even- and odd-parity ILM modes and kink ILM modes. A study is also made of ILM modes in a two-dimensional array of Kerr impurities.

Surface plasmon polariton mechanism for enhanced backscattering of light from one-dimensional randomly rough metal surfaces

Recent experimental results of West and O’Donnell [ J. Opt. Soc. Am. A12, 390 ( 1995)] for the enhanced backscattering of p-polarized light from weakly rough, one-dimensional, random gold surfaces are compared with the predictions of two perturbative calculations of such scattering. The experimental surfaces were fabricated to possess power spectra that are nonzero in only a narrow range of wave numbers about the wave number of the surface plasmon polariton supported by them at the frequency of the incident light. As a consequence, enhanced backscattering that is due to the coherent interference of time-reversed scattering sequences involving counterpropagating surface plasmon polaritons is possible for only a limited range of values for the angles of incidence and scattering. The perturbative calculations used in the comparisons with experiment are the infinite-order calculation of McGurn et al. [ Phys. Rev. B31, 4866 ( 1985)] in the small-roughness approximation and the small-amplitude perturbation theory of Maradudin and Me′ndez [ Appl. Opt.32, 3335 ( 1993)] that is exact to fourth order in the surface-profile function. In both calculations the origin of enhanced backscattering is the coherent interference of multiply scattered surface plasmon polaritons with their time-reversed partners. The good quantitative and qualitative agreement between the theoretical and experimental results, with no fitting parameters, supports the conclusion of West and O’Donnell that their data demonstrate the existence of enhanced backscattering caused by the excitation of surface plasmon polaritons on a weakly rough random metal surface.

Enhanced retroreflectance effects in the reflection of light from randomly rough surfaces

Abstract A review is made of theoretical and experimental work on retroreflection enhancements in the diffuse component of light elastically reflected from randomly rough surfaces. These effects are seen as a narrow peak in the angular distribution of the intensity of diffusely reflected light which is centered about the direction for reflected light motion antiparallel to the original incident beam. This peak is observed in the scattering of light from many different types of rough surfaces and has been studied in fields as diverse as solid state physics, astronomy, geophysics, meterology and radar. Work covering all of these fields will be presented in this review. Retroreflection enhancements arise both from shadow casting properties of surface irregularities and from the phase coherence of retroreflected light. These mechanisms can act to create retroreflection enhancements from rough surfaces of dielectric and/or metallic compositions and of surface disorders characterizable on length scales which are large, comparable to or small compared to the wavelength of the scattered light. Specific discussions will be presented of three types of enhanced retroreflectance: (1) A treatment of the optical glory and Heiligenschein phenomena which are concerned with the meterological and geophysical study of light reflected from clouds and terraine will be given. (2) The theory of the opposition effect, encountered in astronomy as an enhanced retroreflection in the light scattered from atmosphereless planets and space debris, will be used to provide a theoretical basis to understand shadowing effects. (3) A recently discovered phenomenon of enhanced retroreflection from weakly rough metallic mirrors, associated with the Anderson localization of surface waves, is also presented. This last phenomenon and its relationship to the study of the Anderson localization of surface waves will be emphasized throughout our discussions. Similar enhancement effects in the scattering of acoustic waves from rough surfaces and a brief outline of some recent work on optical backscattering enhancements due to the Anderson localization of bulk polariton modes, is also presented.

Intrinsic localized modes in nonlinear photonic crystal waveguides: Dispersive modes

Abstract A discussion is given of the theory of intrinsic localized modes (ILM) for nonlinear waveguide impurities in photonic crystals. Particular attention is made to the determination of the dispersion relation of propagating ILM modes. Both even- and odd-parity ILM modes are considered.