We have constructed and tested a novel particle sizer that employs particle
counting (the time-domain approach) rather than the ensemble-diffraction a
pproach that currently dominates the market in atmospheric-dust particle si
zers. The method does not depend on mechanical devices to restrict particle
s within the sampling volume but instead allows for optical isolation of th
e sampling volume. This technique is useful for atmospheric-dust measuremen
ts for which nonobtrusive measurement is often desirable. (C) 1999 Optical
Society of America.