Heterodyne quasi-elastic light-scattering instrument for biomedical diagnostics

Abstract

The heterodyne technique has a number of advantages over the homodyne technique when an accurate characterization of particle-size distribution (PSD) of heterogeneous systems is required. However, there are problems related to acoustic vibrations that make it difficult to take advantage of the heterodyne technique. An instrument developed for quasi-elastic light scattering (QELS) that uses the optical heterodyning principle is described. Vibration-related problems are considerably reduced because of the incorporation of all optical elements into one solid 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 biological fluids for medical diagnostics is presented as a typical application. A diagnostic analysis of the PSD requires a simultaneous processing of a huge number of QELS data. An original statistical algorithm to accomplish this analysis has been developed. Technical specifications of instrumentation for heterodyne QELS measurement are discussed.

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Laser Correlation Spectroscopy: Nutritional, Ecological and Toxic Aspects

“…In the device used by us, a heterodyne scheme ( Fig. 1) is applied (Lebedev et al, 1997). Helium-neon laser serves as a source of light (2).…”

Laser correlation spectroscopy (LCS) and its clinical perspectives in ophthalmology

“…Laser correlation spectroscopy (LCS) (analogs: spectroscopy of quasi-elastic light scatter, optical mixing spectroscopy, photon-correlation spectroscopy) consists of measurement of spectral characteristics of light scattered in quasi-elastic mode from the spectrum of fluctuation intensity of the recorded light (4)(5)(6)(7)(8)(9). Two schemes of measurements can be used: homodyne (selective recording of the light scattered by the system) and heterodyne (recording of beats between the scattered light and reference fixed high-intensity light).…”

“…The spectrum of light intensity fluctuations is a Fourier-transform of a correlation function of intensity fluctuations of the recorded field. In the device used by us, a heterodyne scheme ( Figure 1) is applied (5). Helium-neon laser serves as a source of light (2).…”

“…Helium-neon laser serves as a source of light (2). is transmitted to a photo recorder (5), and is mixed with the scattered portion. Not the spectrum of light scattered by the studied system, but the spectrum of photoelectric fluctuations at the photo recorder (5) output is directly recorded in LCS.…”