Comparing classical electrodynamic theories predicting deformation of a water droplet in a tightly focused Gaussian beam

Abstract

Optical forces are used to accelerate and trap water droplets in applications such as remote spectroscopy and noninvasive surgery. However, the microscopic deformation of droplets is difficult to predict. In this work, the local electrodynamic impulse imparted by a focused laser beam to a water droplet is numerically modeled via a simulation that invokes intensive conservation of electrodynamic and kinetic momentum. Electrodynamic momentum is modeled locally using a D3Q7 electrodynamic lattice-Boltzmann method, and kinetic momentum is modeled locally using a multi-phase D3Q27 weighted-orthogonal lattice-Boltzmann method. Six different electrodynamic theories are implemented in the simulation domain predicting three unique types of droplet dynamics driven by differences in the direction and distribution of force density. The unique water droplet morphology affects the center-of-mass acceleration of the droplet. This study suggests that empirical measurement of the light-driven acceleration of a droplet may help to validate a single electrodynamic theory.