Characterization of the accretion of material by microparticles using resonant ellipsometry.

An optical technique to characterize the accretion of material by microparticles is described. Experiments on the absorption of water vapor by single levitated polystyrene microparticles are reported as examples of an application of the technique. The optical resonant frequencies of the microparticles are perturbed by the accretion of material and the observed shifts are used to characterize the growth. This technique, resonant ellipsometry, makes use of the polarization character of optical resonant modes to distinguish particle swelling from surface layer formation. The experimental results indicate that water vapor absorbed by polystyrene microparticles diffuses primarily into the particle bulk.