Abstract

The photon correlation function G⁽²⁾(τ) of scattered light from particles suspended in a solution is composed of three terms. By a suitable normalization it is written as where τ is the time interval and 〈N〉 the number of particles in the scattering volume. The first term on the right hand side is the dc-term, the second is the self-beat term, and the third is the number fluctuation term. Both the second and the third terms carry information of velocities of particles. We have weighted the second term by the factor η, which is η ≤ 1, to take into account the effect of the degree of coherence of scattered light. Laser doppler velocimetry and laser speckle velocimetry use the second self-beat term. For such purposes η is taken to close to unity and the number 〈N〉 is large. On the contrary, by reducing η and 〈N〉, the third number fluctuation term is relatively enhanced and can be used for velocimetry ; i.e. the number fluctuation laser velocimetry.

© 1992 Optical Society of America