Self-action of continuous laser radiation and Pearcey diffraction in a water suspension with light-absorbing particles

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

doi:10.1364/oe.22.002267

Abstract

Water suspension of light-absorbing nano-sized particles is an example of a medium in which non-linear effects are present at moderate light intensities favorable for optical treatment of organic and biological objects. We study experimentally the phenomena emerging in a thin layer of such a medium under the action of inhomogeneous light field formed due to the Pearcey diffraction pattern near a microlens focus. In this high-gradient field, the light energy absorbed by the particles induces inhomogeneous distribution of the medium refraction index, which results in observable self-diffraction of the incident light, here being strongly sensitive to the medium position with respect to the focus. This technique, based on the complex spatial structure of both the incident and the diffracted fields, can be employed for the detection and measurement of weak non-linearities.

Highlights

During the past decades, the specific behavior of small particles under the action of light has become a powerful and efficient tool in fundamental and applied optical research
We study experimentally the phenomena emerging in a thin layer of such a medium under the action of inhomogeneous light field formed due to the Pearcey diffraction pattern near a microlens focus
If the disperse medium is situated close to the focal plane of the cylindrical lens, additional modulations of the refraction index in the medium due to the light absorption by the particles becomes strong enough to cause a perturbation of the propagating light beam

Summary

Introduction

The specific behavior of small particles under the action of light has become a powerful and efficient tool in fundamental and applied optical research. The corresponding effects are coupled with self-diffraction, self-focusing and emergence of shock waves Such self-action phenomena accompany the propagation of short powerful laser pulses [20,21,22,23] where, due to high density of the absorbed energy, the medium may be damaged. If the disperse medium is situated close to the focal plane of the cylindrical lens, additional modulations of the refraction index in the medium due to the light absorption by the particles becomes strong enough to cause a perturbation of the propagating light beam As a result, this will induce self-diffraction processes that manifest themselves via the intensity redistribution in the beam leaving the medium. We have performed computer simulation and experimental modeling of this effect for different positions of the sample with respect to the lens focus, and confronting the simulation and experimental data served to measure the non-linear characteristics of the medium

The Pearcey diffraction pattern

Influence of the disperse medium near the lens focus

Radiation wavelength

Conclusion