In situ size determination of single levitated solid aerosols

Abstract

An in situ sizing technique for single levitated solid aerosols is reported. The particle size is investigated in micrometre-sized sodium chloride particles, where the size and state of matter depend strongly on the ambient humidity. The experimental approach makes use of elastic light scattering from the particles that are levitated in an electrodynamic aerosol trap, where the patterns of scattered light are fast Fourier transformed for size determination. It is shown that this approach requires for solid particles short detection times of the scattered Light, typically of the order of 0.1 ms, so that the solid particle can be treated as almost stationary in the trap. Size calibration of the fast Fourier transforms of the light scattering patterns is obtained by correlating the space frequency with the equivalent edge length. Deviations from a linear correlation are interpreted as evidence for the occurrence of non-cubic crystal shapes. This result is in agreement with additional experiments using conventional light microscopy.