Abstract

Particle measurements are of importance in the study of aerosols, combustion processes, and pharmaceuticals. In this report, first we briefly review a simple derivation of an inversion formula from basic principles. We describe a modification to the usual form based upon intensity superposition so that one has a form that is accurate at tiny scattering angles. Then, we present the results of a new study of the wavelength dependence of the optical transform of a particulate distribution. Starting with the idealized amplitude transmittance, p(x−x_m,y−y_m)for a particle at spatial position (x_m,y_m) and taking the Fourier transform, one finds immediately the exponential term given by exp [−i2π(f_xx_m + fY_m)] in which the transform frequencies are f_x = ξν/(Fc) and f_y = ην/(Fc). We show how this exponent contains the essence of the temporal frequency dependence of the speckle pattern for the particulate cloud. We calculate the second moment of the intensity in the optical transform. We prove theoretically that it is possible to measure the axial distribution of a particulate sample simply by gathering optical transform data by using illumination by a tunable laser. This novel technique is then demonstrated with (1) computer simulations and (2) masks with various axial distributions. Some concluding remarks will also be made about the use of neural network software in re mote sensing of particulate sizing and spatial distributions.

© 1992 Optical Society of America