Patent ID: 6177993
Filing Date: 2001-01-23
Classification: G01N

Abstract:
A method for enhancing a detected signal from light scattered from a particle on an object, comprising:determining an approximate first angular distribution of particle scatter signal produced by a first portion of a laser beam scattered from a particle, wherein said laser beam has an angle of incidence with respect to said object;determining an approximate second angular distribution of object scatter noise produced by said first portion of said laser beam scattered from said object;calculating a ratio of said approximate first angular distribution to said approximate second angular distribution to produce an approximate third angular distribution of particle scatter signal to object scatter noise;placing a detector at a position chosen from said approximate third angular distribution;directing said first portion of said laser beam at said angle of incidence to said particle to produce scattered light;frequency shifting at a frequency difference a second portion of said laser beam with respect to said first portion of said laser beam to produce a frequency shifted laser beam;directing said frequency shifted laser beam at said object to produce specularly reflected light directed at said detector; anddetecting optical heterodyning, at said frequency difference, between a portion of said scattered light and a portion of said specularly reflected light to produce enhanced scattered light signal from said detector.