Measurement of the velocity difference by photon correlation spectroscopy: an improved scheme

Homodyne photon correlation spectroscopy is used to measure the velocity difference delta v(l) over varying distance l. Different length scales are probed when the magnification factor M and the widthS of a slit in the collecting optics are varied. The measured intensity autocorrelation function is found to be of scaling form for different values of M, provided S is kept at a value below the critical width S-c. Anew convenient collecting optics is devised to expand the variable range of l up to 2 decades, over which delta v(l) can be accurately measured. The new scheme is useful for the study of turbulent and other self-similar flows. (C) 1997 Optical Society of America.