<title>Optical method for nondestructive measurement of a velocity distribution in a flow of scattering particles</title>

Abstract

An optical method is suggested for nondestructive measurement of a velocity distribution in a flow of light scattering particles. Photocurrent spectrum of a point photodetector is found to reproduce a velocity distribution function of scattering particles. 1.DESCRIPTION OF METHODNow optical methods are widly used for nondestructive testing of flows of scattering particles. We would like to offer the new simple method of measurement of a velocity distribution in a light scattering flow.Let us consider one dimentional flow of scattering particles moving in the direction of axis in the plane z=O. Light field in this plane is formed by a plane monochromatic wave with wave vector directed along axis z,i.e. along the normal to the plane where scattering particles move.Complex amplitude of the light field in the plane z=O is g0() =1. Small photodetector is situated at the point x of observation plane z=const>O. Scattering particles, all of the same size a, are randomly placed along axis .Let be coordinate of n-th particle at moment 1=0. Then particle coordinate versus time iswhere v, is the particle velocity. Transperency function of a single particle can be written as m(4,t) = 1 -a(' vt) , (1) where Pa() = 1 if I I ' Pa(') = 0 if I I > . Let us consider the particles flow as a randomly changed screen. Then its transparency function is m(,t) = ---vat)Wave complex amplitude on the output plane z=O is g(,t)= g0() m(x,O.The observation plane is distanced to the far diffraction zone with respect to the scatterer size a: a2(3)We find the complex amplitude at point x of the observation plane (the far diffraction zone approximation of Kirhgoff integral ):.kx2 exp(z----)) 0-81 94-1399-2/93/$6.0O SPJE Vol. 2108 / 303 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/17/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx