Backscattering enhancement from a randomly rough surface

How time-reversal-invariance violation leads to enhanced backscattering with increasing openness of a wave-chaotic system

We report on the experimental investigation of the dependence of the elastic enhancement, i.e., enhancement of scattering in the backward direction over scattering in other directions, of a wave-chaotic system with partially violated time-reversal (T) invariance on its openness. The elastic enhancement factor is a characteristic of quantum chaotic scattering which is of particular importance in experiments, like compound-nuclear reactions, where only cross sections, i.e., the moduli of the associated scattering matrix elements, are accessible. In the experiment a quantum billiard with the shape of a quarter bow tie, which generates a chaotic dynamics, is emulated by a flat microwave cavity. Partial T-invariance violation of varying strength 0≤ξ≲1 is induced by two magnetized ferrites. The openness is controlled by increasing the number M of open channels, 2≤M≤9, while keeping the internal absorption unchanged. We investigate the elastic enhancement as function of ξ and find that for a fixed M it decreases with increasing T-invariance violation, whereas it increases with increasing openness beyond a certain value of ξ≳0.2. The latter result is surprising because it is opposite to that observed in systems with preserved Tinvariance (ξ=0). We come to the conclusion that the effect of T-invariance violation on the elastic enhancement then dominates over the openness, which is crucial for experiments which rely on enhanced backscattering, since, generally, a decrease of the openness is unfeasible. Motivated by these experimental results, we performed theoretical investigations based on random matrix theory which confirm our findings.

Brewster's scattering angle in scattered waves from slightly rough metal surfaces

Brewster's scattering angle in electromagnetic wave scattering from slightly random metal surfaces is investigated by means of the stochastic functional approach. While there are dips due to Brewster's scattering angle in scattering profiles from dielectric surfaces, Brewster's scattering angle does not exist in scattering from metal surfaces. However, the dips can exist in scattering from rough metal surfaces with the optically denser medium to convert evanescent wave into radiative wave.

Coherent backscattering of optical second-harmonic generation with long-range surface plasmons

We report the observation of coherent backscattering of optical second-harmonic generation that is due to excitation of the long-range surface plasmon mode at a silver-quartz interface. A peak-to-background ratio of greater than 2 is seen, which is possible for a coherent scattering process in nonlinear optics. The backscattering pattern has an angular half-width of 15 mrad in the incident plane but 90 mrad in the transverse plane. This effect is consistent with simple wave-vector considerations. Backscattering is observed only over a limited range of silver film thicknesses that correspond to a maximum propagation length for the surface mode.