Optohydrodynamics of soft fluid interfaces : Optical and viscous nonlinear effects

TL;DR

This paper numerically investigates the optohydrodynamic behavior of soft fluid interfaces under laser radiation pressure, revealing nonlinear effects and interface morphologies validated by experiments.

Contribution

It introduces a numerical model that captures nonlinear optical effects on fluid interfaces, providing new insights into interface shapes and dynamics under laser actuation.

Findings

Different interface morphologies from needle-like to finger-like shapes.

Nonlinear dependence of optical pressure on incidence angle affects deformation.

Viscosity ratio influences transient deformation time.

Abstract

Recent experimental developments showed that the use of the radiation pressure, induced by a continuous laser wave, to control fluid-fluid interface deformations at the microscale, represents a very promising alternative to electric or magnetic actuation. In this article, we solve numerically the dynamics and steady state of the fluid interface under the effects of buoyancy, capillarity, optical radiation pressure and viscous stress. A precise quantitative validation is shown by comparison with experimental data. New results due to the nonlinear dependence of the optical pressure on the angle of incidence are presented, showing different morphologies of the deformed interface going from needle-like to finger-like shapes, depending on the refractive index contrast. In the transient regime, we show that the viscosity ratio influences the time taken for the deformation to reach steady state.