A novel particle sizing technique based on near field scattering

We present a novel technique for particle sizing, based on recent studies about near field speckles, that is simpler than the existing light scattering methods. We first recall the results about the so called near field scattering (NFS) condition for the light scattered by a disordered sample, discussing the main features of this remarkable region of the scattered light. Then we present the two standard configurations (homodyne and heterodyne NFS) adopted for carrying out NFS measurements. The two configurations are critically discussed and the great advantages of the heterodyne scheme are emphasized, such the extremely simple layout, the rigorous subtraction of stray light and the almost zero alignment requirements. Results obtained with suspensions of calibrated polystyrene spheres are presented and discussed.