Phase characteristics of a spherical particle passing through the crossed region of two coherent beams

Light with periodic intensity is scattered when a spherical particle passes through the cross-over region of two coherent laser beams. Photodetection of this light produces a periodic signal of varying amplitude. The phase of the signal varies with the particle diameter and reflective index, the beam crossing angle and wavelength, and the position and size of the scattered light collecting lens. In this paper the phase variation with respect to the particle absorptive index of retraction, collecting lens size and beam crossing angle is calculated using both Mie scattering theory and reflection theory. The two theories show good agreement in phase predictions, especially for large absorptive indices and for small collection lenses. Both theories predict phase to be inversely proportional to the beam crossing angle