HETERODYNE QUASI-ELASTIC LIGHT-SCATTERING INSTRUMENT FOR BIOMEDICAL DIAGNOSTICS

The heterodyne technique has a number of advantages over the homodyne technique when an accurate characterization of particle-size distribut ion (PSD) of heterogeneous systems is required. However, there are pro blems related to acoustic vibrations that make it difficult to take ad vantage of the heterodyne technique. An instrument developed for quasi -elastic light scattering (QELS) that uses the optical heterodyning pr inciple is described. Vibration-related problems are considerably redu ced because of the incorporation of all optical elements into one soli d optical block. A real-time correlation analysis of the photocurrent fluctuations is performed by a PC-embedded analog-to-digital converter card with a digital signal processor. Investigation of the PSD in bio logical fluids for medical diagnostics is presented as a typical appli cation. A diagnostic analysis of the PSD requires a simultaneous proce ssing of a huge number of QELS data. An original statistical algorithm to accomplish this analysis has been developed. Technical specificati ons of instrumentation for heterodyne QELS measurement are discussed. (C) 1997 Optical Society of America.