Optical properties of a thermocapillary depression

Abstract

An axisymmetrical thermocapillary depression is induced by a He-Ne laser beam in a plane-parallel layer of a transparent liquid on an absorbing substrate. The focal length of the central part of this depression in the form of a concave mirror is studied as a function of thickness of the benzyl-alcohol layer and beam power. At a laser power of 3.5–16.5 mW, the focal length increases almost linearly with the layer thickness changing from 200 to 1000 µm. In this range of thicknesses, an increase in the beam power leads to a decrease in the focal length following a power law with an exponent close to −0.8.