Photon cross-correlation spectroscopy to 10-ns resolution

We describe a low-cost modification based on the research of Arecchi et al. [Opt. Commun. 3, 284-288 (1971)] on a standard photon correlation spectroscopy setup for measuring small (similar or equal to 1%) and fast (resolution, similar or equal to 10 ns) light fluctuations. Details of the electronics and optics permit the apparatus to be easily reproduced. Careful tests show that spurious correlations of less than or equal to 1% can be achieved with standard detectors only when taking precautions with the electronics. Moreover, measurements on latex spheres, ellipsoids, and protein solutions show that fast and very small light fluctuations (similar or equal to 1-5%) can be studied versus scattering vector and light polarization. (C) 1999 Optical Society of America.