Interferometric system for precise submicrometer particle sizing.

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 mum. Experimental results obtained with polystyrene spheres in the range of diameters 0.16-0.71 mum 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 mum.