Light scattering from a drop with an embedded particle and its exploitation in the time-shift technique

Abstract

This study is devoted to light scattering from drops with an embedded particle, as would be expected in an encapsulation/coating process or with spraying of metallic paints. A ray-tracing approach is taken, in which the polarization and intensity of all rays impinging onto a defined detector aperture are documented, allowing the signal generation arising from the drop passing through a plane wave or focused Gaussian beam to be simulated. For validation of the ray-tracing code, comparisons are drawn to scattering from pure liquid drops, obtained using the Lorenz–Mie solution. When using a highly focused incident beam, the scattering corresponds to the optical arrangement of the time-shift technique and allows the capabilities of that technique to measure drops with embedded particles to be explored. The resulting detector signals for a drop with an embedded spherical particle (encapsulated particles) or an embedded circular flake (metallic paint drop) have been simulated. These signals are compared with signals arising from pure liquid drops and features are identified which could be exploited for detecting the embedded particles using the time-shift technique.