Numerical simulation of the optical radiation absorption by dielectric microcapsules of different spatial shapes

Abstract

The heating dynamics a micron-sized two-layer capsules simulating transport microcontainers with water-containing load and light-absorbing composite shell exposed to a near-IR laser pulse (wavelength 800 nm) is theoretically studied. Both single microcapsules and the microassemblies of particles with various spatial shapes and different packing densities are considered. Using FDTD and FEM calculations, the numerical simulations of the optical field distribution inside and near the microcapsules are carried out, and the temporal dynamics of the temperature profiles of microparticles shells is obtained. Based on the simulation results, one can conclude that the particle morphology introduces specificity in the spatial profile of the optical field and the distribution of light absorption regions. Variation in the geometric shape of a capsule leads to dramatic changes in the distribution of absorbed light energy and, accordingly, particle temperature field. In order to increase the efficiency of absorption of optical radiation in capsule volume and to obtain the maximum heating of absorbing shells, the capsules of cubic, cylindrical and partly rectangular shapes are preferable. Thus, having a 100-fs laser pulse with energy of only 20 μJ it becomes possible to heat a cylindrical microcapsule to the temperature of thermal destruction of its polymeric shell (~ 410 K). Worthwhile notice, the water-filling of a capsule core remains cold. At the same conditions, the ellipsoid-shaped capsule is heated to multiple lower temperatures (~ 340 K).