Estimation of particle trajectory effects and their reduction using polarization in phase Doppler particle measurements

Phase Doppler methods that measure the diameter of moving spherical particl es are sensitive to particle trajectory effects that cause a phase error un der Gaussian beam illumination. This error results from the interference be tween reflected and refracted rays from the particle. We first numerically estimate the particle trajectory effect using the geometrical optics approx imation and the generalized Lorenz-Mie theory (GLMT) and, then, discuss the optimum measurement conditions that minimize the phase error. We next theo retically and experimentally investigate a method for reducing the trajecto ry effect using the separation of reflected and refracted rays on the basis of the polarization change. Experimental results show the usefulness of th is method. (C) 1999 Society of Photo-Optical Instrumentation Engineers. [S0 091-3286(99)02111-X].