Far-field temporal dynamics of a laser beam passed through a thin nanocolloidal layer

Abstract

We report on the experimental results of the temporal dynamics and formation of far-field diffraction patterns obtained when a low-intensity laser beam passes through a thin cell with metallic nanocolloids. The steady state structure of the intensity distribution on a distant screen is shown to be formed in a few seconds starting from the moment of laser beam incidence on the colloid and consists of several coaxial bright and dark rings. The ring’s diameter and number are varied depending on the solvent type and optical thickness of the colloid. The diffraction patterns depend also on the particle concentration and laser power. The theoretical interpretation of the observable peculiarities of diffraction pattern dynamics is carried out based on the free-space Kirchhoff diffraction integral and the analytical solution of the heat transfer equation for a light absorbing medium.