Bounded beams reflected at the interface between two dielectric media can undergo lateral displacements, focal shifts, angular deviations, changes in the beam waist size and complex amplitude. These effects are examined for beams incident from a linear medium onto a nonlinear defocusing Kerr-type material, where the nonlinear medium changes are supposed to be homogeneously non-local. An exact solution to the reflection problem is numerically iterated by a sequence of solutions to the respective linear problems and a rigorous first-order analysis of the non-specular phenomena is also given. The beam-interface interaction is described in terms of the Wigner distribution function invariant with respect to the nonspecular ABCD transformation. T h e results show that, for some specified beam parameters, the beam reflection may exhibit bistable switching, which is accompanied by bistable changes in all the non-specular effects.
IntroductionThe nonlinear interface (NLI) is commonly known as a plane interface between a region of larger linear index of refraction that is not intensity dependent and a region of smaller nonlinear index of refraction which is Kerr-type intensity dependent. When a light beam is incident from the linear region at an angle smaller than the critical angle of reflection, the N L I persists in the partial transmission (PT) state, otherwise the total internal reflection (TIR) occurs. Owing to induced changes in the nonlinear refractive index the switching from T I R to P T and vice versa can be achieved by increasing or reducing the incident beam power. Since the N L I does not involve any resonator element it offers the possibility of ultrafast broad-band photonic switching, limiting, scanning and other signal processing operations.Much work has been done over the last two decades to model and understand the complexity of such a seemingly simple structure. Among other interesting phenomena the potential bistable switching has attracted a great deal of attention in the first place. Optical bistability at the N L I was first predicted by Kaplan [ l ] who developed a plane wave analytic theory of reflection and transmission at the NLI. Further experimental and theoretical research [2-81 on the interaction of spatially localized beams with the N L I appeared rather inconclusive and did not confirm the bistable behaviour of the N L I in two-dimensional (2D) and threedimensional (3D) geometries. Instead, multiple thresholds with low switching contrast and beam breakup in the nonlinear local self-focusing Kerr-type medium were observed.