Ellipticity-dependent laser-induced optical gyrotropy in AgCl thin films doped by silver nanoparticles

A laser-induced optical gyrotropy is observed in light-sensitive waveguide AgCl–Ag thin films, as a result of spontaneous periodic nanostructure formation, which is the product of interaction of a polarized incident light with the film’s substances. Interference of the incident He–Ne laser beam with the excited TE-modes of the waveguide AgCl–Ag thin film and migration of Ag nanoparticles to minima of the interference pattern results in formation of spontaneous periodic nanostructures. Results of our investigation indicate that, in our case, the strength of induced optical rotation depends on the ellipticity of the polarization state of the incident laser beam. It is found that the induced optical activity is caused by two factors in the film: (1) the induced anisotropy; and (2) formed chiral complex planar nanostructures. The portion of each factor in the induced optical gyrotropy depends on the polarization state of the incident laser beam. We have shown that, under incidence of circular polarized light, the chirality is the most efficient factor to produce gyrotropy, but for elliptical polarized incident light, the induced anisotropy, which increases dissymmetry of the film, plays essential role. In this connection, the induced circular dichroism of the samples and optical rotation of the linear polarized probe beam are measured. In this regard, the induced birefringence (∆n) of the samples is measured. The present study proposes a new candidate for meta-materials and also a simple method for recording the ellipticity and sign of rotation of the polarized incident light.