Particle Displacement And Velocity Measurement Using Holography

Abstract

A method of measuring particle displacements and velocities in the optical Fourier transform plane of an in-line far-field hologram is examined. The Fourier transform of a doubly exposed hologram is calculated, and it is shown that each particle pair related by translation contributes a set of cosine fringes to the total diffraction pattern. The fringe frequency and orientation are related to the magnitude and direc-tion of a given particle's displacement or velocity. The intensity in the optical transform plane is detected with a TV camera whose output is digitized and then linked to a computer for analysis. Particle velocities in one and two dimensions are measured, and experimental results are presented. Also, resolution limits are established by evaluating the minimum detectable difference in particle displacement.