Abstract

A multi-channel real-time correlator is the most important unit of a photon correlation spectrometer. Correlator design defines basic possibilities and the cost of spectrometer. Modern level of electronics allows to design single-board correlators, plugged into a standard IBM computer. We have created and now manufacture a number of single-board correlators. Precision correlator (8-bits, 72-216 channels, minimal real sample time 50 ns) includes multiple-tau mode, base-line channels, cut of dust mode. It is based on specific CMOS IC designed on our scheme. We also manufacture several simpler versions (4-bit and 1-bit) for industrial applications and university labs. Our devices are used for study of phase transitions and critical phenomena in liguid crystals and surfactant solutions. Moreover, the correlators are used in several research and industrial laboratories in some non-trivial cases: dark suspensions, biological non-transparent solutions, etc.. Many applications demand the analysis of particle size distribution (PSD). We usually use modified cummulant method with original fitting procedure. We studied various PSD analysis methods including inverse Laplace transform, regularization and eigen function methods. Theoretically the ideally (without errors) measured auto-correlation function (ACF) contains full information about PSD. Real ACF has experimental errors within 0.1-1%. In this case some information about PSD will be lost. For measurement accuracy about 0.1% only 3 parameters of PSD are reliable. So, all methods which represent PSD in the form of any function should use some additional assumptions and they do so. These assumptions often do not correspond to reality. As a result the obtained PSD sufficiently differs from the real distribution. Cummulant method is free from this defect. The distribution parameters obtained by this method are correct.

© 1992 Optical Society of America