Self-diffraction of continuous laser radiation in a disperse medium with absorbing particles

O V Angelsky,S G Hanson,C Yu Zenkova,A Ya Bekshaev,A P Maksimyak,P P Maksimyak

doi:10.1364/oe.21.008922

Abstract

We study the self-action of light in a water suspension of absorbing subwavelength particles. Due to efficient accumulation of the light energy, this medium shows distinct non-linear properties even at moderate radiation power. In particular, by means of interference of two obliquely incident beams, it is possible to create controllable phase and amplitude gratings whose contrast, spatial and temporal parameters depend on the beams' coherence and power as well as the interference geometry. The grating characteristics are investigated via the beams' self-diffraction. The main mechanism of the grating formation is shown to be thermal, which leads to the phase grating; a weak amplitude grating also emerges due to the particles' displacements caused by the light-induced gradient and photophoretic forces. These forces, together with the Brownian motion of the particles, are responsible for the grating dynamics and degradation. The results and approaches can be used for investigation of the thermal relaxation and kinetic processes in liquid suspensions.

Highlights

Interaction of laser radiation with a medium containing subwavelength absorptive particles is accompanied by a set of non-linear phenomena characterized by the square-law dependence on the electromagnetic field amplitudes
We study the self-action of light in a water suspension of absorbing subwavelength particles
The main mechanism of the grating formation is shown to be thermal, which leads to the phase grating; a weak amplitude grating emerges due to the particles’ displacements caused by the light-induced gradient and photophoretic forces

Summary

Introduction

Interaction of laser radiation with a medium containing subwavelength absorptive particles is accompanied by a set of non-linear phenomena characterized by the square-law dependence on the electromagnetic field amplitudes. They originate from diverse physical mechanisms: electro- and magnetostriction, thermal effects due to light absorption, concentrationdeformation mechanism, temperature gradients, etc [1]. The concentration-deformation mechanism connected with the medium density variations owing to the concentration of photoexcited charge carriers [4] plays a noticeable role only when the carriers’ life time is higher than the characteristic time scale of the light intensity modulations This preferably takes place in semiconductors exposed to picosecond laser pulses

Objectives

Results

Conclusion