Abstract

It is known that the Wood’s anomalies can be observed on "permanent” diffraction gratings under certain conditions [1,2]. These anomalies may occur both in TM and TE polarizations of incident light and can be of different types "Rayleigh”, "leaky-wave resonance” and "Bragg-angle” types of anomalies. Stimulated Wood’s anomalies [3] can develop on the surface illuminated by a single laser beam of sufficient intensity as spontaneous highly periodic surface ripples Conventionally, laser light self-diffraction on two-wave induced dynamic gratings in a thin nonlinear film is studied in the Raman-Nath approach not taking into consideration the possibility of any Wood’s anomalies [4]. We have shown that Wood’s anomalies can be observed not only on the “permanent” diffraction gratings but also on the two-wave induced dynamic gratings [5]. We consider the Wood’s anomalies of "leaky-wave resonance” type to be related to excitation of surface polaritons or guided waves in the thin slab by means of induced dynamic gratings. These anomalies occur when one or two counterpropagating off-Bragg self-diffraction orders skim along the illuminated thin slab at some angles of degenerate two incident wave mixing. These leaky-wave resonances give rise to enhancement of local field and all nonlinear processes on the surface. The self-diffraction of laser light at these resonances exhibits instabilities which were not considered previously. The goal of this report is to present results of study of these new phenomena which would be important for nonlinear optical probing of surfaces and multiwave mixing processes in thin films.

© 1996 IEEE