Andrei V. Shchegrov

Photofabrication of random achromatic optical diffusers for uniform illumination

We propose a method of designing two-dimensional random surfaces that scatter light uniformly within a specified range of angles and produce no scattering outside that range. The method is first tested by means of computer simulations. Then a procedure for fabricating such structures on photoresist is described, and light-scattering measurements with the fabricated samples are presented. The results validate the design procedure and show that the fabrication method is feasible.

Resonant scattering of electromagnetic waves from a rectangular groove on a perfectly conducting surface

Abstract The frequencies of the electromagnetic surface shape resonances of both p- and s-polarizations associated with a rectangular groove on the otherwise planar surface of a perfect conductor, and the scattering of a Gaussian beam of p- and s-polarized light from the same groove, are calculated by both a modal approach and a numerical method based on Greens second integral identity. On the basis of the results of these calculations we show that the dips in the frequency dependence of the intensity of the scattered light in s-polarization for fixed angles of incidence and scattering found in earlier work by Zuniga-Segundo and Mata-Mendez [Phys. Rev. B 46 (1992) 536], and which we find in the scattering of p-polarized light as well, do not occur at the frequencies of the surface shape resonances as asserted by these authors, and we give the correct explanation for these features. In addition, we show that while the dips in the frequency dependence of the intensity of the scattered light associated with s-polarized surface shape resonances are masked by the dips found by Zuniga-Segundo and Mata-Mendez, this is not the case for dips associated with p-polarized surface shape resonances. The latter should therefore be observable in experimental studies of the scattering of p-polarized light from a rectangular groove on an otherwise planar surface of a highly conducting metal.

Design of one-dimensional band-limited uniform diffusers of light

We present two methods for generating numerically a one-dimensional random surface, defined by the equation x3=ζ(x1), that has a prescribed probability density function of slopes. This problem arises in the design of a diffuser that scatters light uniformly within a range of scattering angles and produces no scattering outside this range. Numerical calculations of the scattering of light from random surfaces generated by these approaches show that the scattered intensity, indeed, has a rectangular distribution as a function of the scattering angle.

Speckle patterns produced by weakly rough random surfaces: existence of a memory effect twin peak in the angular correlations and its consequences

Abstract A new peak, as strong as the well known memory effect peak, is found in the angular correlation of light and other waves scattered from slightly rough random surfaces. The existence of this peak does not depend on whether there is single or multiple scattering, nor on whether the surface is dielectric or metallic, nor on the polarization. However, unlike the memory effect peak, it decreases as the rms surface height increases in wavelength units. Hence, it does not appear in the scattering of waves from highly rough surfaces. Its existence also affects the foundations of the theory of speckle patterns, as it implies that the second order statistics of the scattered field, though being Gaussian, is not circular, and hence the commonly used factorization approximation is never valid when the surface is slightly rough. Nevertheless, this peak cannot be inferred from speckle contrast observations, and thus it does not affect this quantity.

Scattering of electromagnetic waves from a one-dimensional random metal surface with a localized defect

We study theoretically the scattering of a beam of s-polarized light from a one-dimensional random metal surface with a localized deterministic defect. We carry out numerical calculations of the far field intensity, using a formally exact technique based on Greens second integral identity and statistical ensemble averaging. Our results obtained for very rough surfaces show that the backscattering peak in the differential reflection coefficient for the scattered light almost does not change for small angles of incidence. However, for larger angles it undergoes significant enhancement due to the presence of the defect, which phenomenon we attribute to a form of the corner cube effect. We also consider how the presence of a deterministic defect changes the behavior of the angular intensity correlation function for the scattered light. We are primarily interested in the changes of the memory effect and the time-reversed memory effect peaks. We show that the defect can enhance or suppress these peaks depending on the relative positions of the light sources and the points of observation. The explanation of these results is again associated with the corner cube effect.

Enhanced backscattering of light from a randomly rough interface between a dipole-active medium and a dielectric

The enhanced backscattering of light from randomly rough metal surfaces, which manifests itself as a well-defined peak in the retroreflection direction in the angular distribution of the intensity of the light scattered incoherently has attracted a great deal of attention recently. The backscattering phenomenon is attributed to the coherent interference of multiply-scattered surface plasmon polaritons excited on a metal surface with their time-reversed partners. The coherent interference of multiply-scattered lateral waves excited in the scattering of light from strongly rough dielectric surfaces is known to lead to an enhanced backscattering peak in the angular distribution of the intensity of s-polarized light scattered from them. In this paper we present an analytical theory of the scattering of light from a one- dimensional randomly rough interface between two media. One of the media is a dipole-active medium that is characterized by a frequency-dependent dielectric function, that is negative in a restricted frequency range, while the other is characterized by a frequency-independent, real, positive dielectric constant. We assume that the interface profile function is a single-valued function of the coordinate in the mean plate of the interface that is normal to its grooves and ridges, and constitutes a zero-mean, stationary, Gaussian random process. We assume that either p- or s-polarized electromagnetic waves are incident on the interface from the medium whose dielectric constant is frequency-independent. We study the angular distribution of the light that has been scattered incoherently as a function of the frequency of the incident light. The evolution of the enhanced backscattering peak in the case of p-polarized incident light as the frequency of the incident light is tuned through the frequencies of the dipole-active excitations in the medium whose dielectric function is frequency-dependent, is studied. Different mechanisms for the formation of the enhanced backscattering peak in different frequency regions are discussed.

Spectral changes of light scattered from a random metal suface in the Otto attenuated total reflection configuration

We investigate theoretically changes in the spectrum of light scattered from a system with a random surface (the Wolf effect). The system we consider is the Otto attenuated total reflection configuration that is widely used to couple the incident light to surface polaritons. The angular dependence of the intensity of the light scattered incoherently from this system exhibits sharp, intense peaks at the angles of optimum excitation/radiation of the surface polaritons supported by it. In the vicinity of each of these resonance angles the spectrum of the scattered light is red-shifted for scattering angles larger than this angle, and is blue-shifted for scattering angles smaller than this angle. The magnitude of the shift is three to four orders of magnitude larger than that predicted for disordered volume media. We conclude that the Otto attenuated total reflection configuration is another example of bounded systems with random surfaces which are more attractive subjects for experimental studies of the Wolf effect than systems with a single random surface or disordered volume systems.

Signatures of electromagnetic surface-shape resonances in scattering of pulsed beams from surface defects

We predict theoretically that electromagnetic resonances supported by surface defects can be detected experimentally by study of the scattering of electromagnetic pulses from these defects, and we formulate the optimal conditions for such experiments. Numerical scattering simulations confirm that the proposed scattering probes unambiguously identify resonance signatures. The approach that we suggest proves to be superior to conventional analysis of features in the dependence of the far-field intensity of scattered monochromatic light on its frequency, since these features do not necessarily point at resonant frequencies.