Simulation of an optically induced asymmetric deformation of a liquid-liquid interface

TL;DR

This paper investigates how high-intensity laser radiation pressure causes asymmetric deformations in liquid-liquid interfaces, breaking the previously assumed invariance with respect to beam direction, using numerical simulations and experimental validation.

Contribution

It introduces a Boundary Integral Element Method simulation to analyze large deformations and compares results with experiments, revealing asymmetry in interface behavior at high laser intensities.

Findings

Invariance of interface deformation breaks at high laser intensities.

Numerical simulations agree with experimental data for large deformations.

Asymmetry depends on the direction of laser beam propagation.

Abstract

Deformations of liquid interfaces by the optical radiation pressure of a focused laser wave were generally expected to display similar behavior, whatever the direction of propagation of the incident beam. Recent experiments showed that the invariance of interface deformations with respect to the direction of propagation of the incident wave is broken at high laser intensities. In the case of a beam propagating from the liquid of smaller refractive index to that of larger one, the interface remains stable, forming a nipple-like shape, while for the opposite direction of propagation, an instability occurs, leading to a long needle-like deformation emitting micro-droplets. While an analytical model successfully predicts the equilibrium shape of weakly deformed interface, very few work has been accomplished in the regime of large interface deformations. In this work, we use the Boundary Integral Element Method (BIEM) to compute the evolution of the shape of a fluid-fluid interface under the effect of a continuous laser wave, and we compare our numerical simulations to experimental data in the regime of large deformations for both upward and downward beam propagation. We confirm the invariance breakdown observed experimentally and find good agreement between predicted and experimental interface hump heights below the instability threshold.