Method to measure time-dependent scattering cross sections of particles evaporating in a laser beam

We develop a new method of measuring the time-dependent solid angle scattering cross section for detection (Delta C-sca(t)) Of individual particles flowing across a Gaussian laser beam. This method is based on the principle that the normalized derivative of the scattering signal (S'/S) measured by an instrument can be decomposed into the normalized derivative of the incident irradiance (I'll) and that of the scattering cross section Delta C'(sca)/Delta C-sca). For evaporative particles, S'/S = I'/I holds true until evaporation starts at a certain position in the laser beam. The I (t) for individual particles is determined from I'/I, which is extracted from S'/S. Delta C-sca(t) is derived from I (t) and S(t). We apply the method to particles with and without evaporation using a single-particle soot photometer. The robustness of the method is confirmed through results for non-evaporative particles. For evaporative particles, derived Delta C-sca values before the onset of evaporation are compared to Mie theory. (C) 2007 Elsevier Ltd. All rights reserved.