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Following a recently exploited line of thought, we present an interferometric system for particle sizing in the submicrometer region. The phase of the field that results from the interference between the incident and the scattered waves is measured through a heterodyne detection scheme in a Mach-Zehnder-type interferometer. We explored the possibility of extending previous work on this subject to the case of larger particles, i.e., particles larger than 0.5 [[micro]meter]. Experimental results obtained with polystyrene spheres in the range of diameters 0.16-0.71 [[micro]meter] are reported and compared with theoretical predictions. We show that in this range univocal detection of the particle size is not successful because the phase versus particle-size plot exhibits a maximum in correspondence to diameters close to 0.5 [[micro]meter]. Key words: Light scattering, particle sizing, interferometry.

Particle-size distribution and the concentration of polystyrene particles suspended in water were accurately recovered from the inversion of spectral extinction data measured with a commercial spectrophotometer. The instrument was modified by placing a spatial filter in the collection optics to prevent low-angle scattered light from affecting the measurement of transmitted power. The data were inverted by use of a nonlinear iterative algorithm. When the extinction coefficient is measured in the k range of 0.3-1.1 [[micro]meter], the particle distributions can be retrieved over a diameter range of 0.6-2.8 [[micro]meter] for a wide interval of sample concentrations. The average diameters are recovered with a precision of better than [+ or -]1% and with accuracies consistent with the uncertainties by which the nominal diameters are known. The relative standard deviations of distributions corresponding to monodisperse samples are [+ or -]5-10%, whereas the accuracy on the measured concentrations is [approximately]5%. Key words: Particle sizing, inversion algorithm, spectral extinction.