A differentially pumped particle inlet for sampling of atmospheric aerosols into a time-of-flight mass spectrometer: Optical characterization of the particle beam

Abstract

Two methods of characterizing the particle beam generated with a differentially pumped particle inlet are presented. Both methods are based on optical scattering of a laser beam by the particle beam. The first method images a time integrated scatter signal from the entire particle beam onto a charge coupled device (CCD), and an Abel inversion is performed on the image data to arrive at the radial particle density distribution in the beam. The second method, based on counting individual (particle) scatter pulses, yields the radial particle density directly. Initial results of the performance of the particle inlet are reported for particles with diameters between 40 and 800 nm. Under optimal working conditions, particle beams were generated with a full angle divergence on the order of 1-2 mrad. The width, measured 285 mm downstream from the exit of the particle inlet, was 250 μm, half width at half maximum (HWHM).