Abstract

In the past five years the optical apparatus, heart of a photon correlation spectroscopy (PCS) experiment, has undergone major advances through the deployment of optical fibers. The once cumbersome apparatus comprising of bulk optics, photomultipliers, and goniometers has been revolutionized through the miniaturization achievable by advances in semiconductor lasers, fiber optics and semiconductor photon detectors. Tanaka and Benedek¹ were the first to report the use of optical fibers in PCS systems. The first fiber optic back scatter system, developed by Dyott², was applied to the characterization of size^3-4, and motility⁵. Auweter and Horn⁶ modified the Ross et al.³ device by replacing the "hole-in-mirror" with a multimode directional fiber optic coupler. Dhadwal⁷ used a graded index microlens to replace the fiber coupler. These fiber optic back scatter systems provide a homodyne detection of the scattered light, and as such are limited in their effectiveness in the study of concentrated suspension. In order to alleviate this difficulty Dhadwal et al.⁸ developed a self-beating back scatter fiber optic probe, which has proved effective in the study of concentrated aqueous suspensions of polystyrene spheres, as well as in the study of proteins systems in excised, but intact, human eye lenses⁹. A generalized fiber optic receiver was developed independently by Brown¹⁰ and by Dhadwal and Chu^11-12. In both devices an optical fiber is positioned in the focal plane of lens. Brown opted for the use of a plano-convex lens, while Dhadwal and Chu employed a cylindrical graded index microlens. These probes have added versatility and compactness to the optical system, without sacrificing detection efficiency. Dhadwal and Ansari¹³ used a linear array of optical fibers positioned in the back focal plane of a graded index microlens to provide simultaneous measurements of the scattered light at 11 scattering angles. Haller et al¹⁴ used large diameter optical fibers in a general purpose laser light scattering facility.

© 1992 Optical Society of America