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 (ΔCsca(t))(ΔCsca(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)(S′/S) measured by an instrument can be decomposed into the normalized derivative of the incident irradiance (I′/I)(I′/I) and that of the scattering cross section (ΔCsca′/ΔCsca). For evaporative particles, S′/S=I′/IS′/S=I′/I holds true until evaporation starts at a certain position in the laser beam. The I(t)I(t) for individual particles is determined from I′/II′/I, which is extracted from S′/SS′/S. ΔCsca(t)ΔCsca(t) is derived from I(t)I(t) and S(t)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 ΔCscaΔCsca values before the onset of evaporation are compared to Mie theory.