Photon Correlation Spectroscopy Using Optical Heterodyne Detection

The detection by optical heterodyning of laser light scattered from solutions of macromolecules offers significant improvement in statistical accuracy over the more usual self-beating method. Nevertheless the heterodyne technique is not commonly used because of the supposed ifficulties associated with stable and efficient mixing of the scattered light with a local oscillator beam. We have carried out an experimental comparison of several methods of mixing the two beams, using very dilute solutions of polystyrene latex spheres as scatterers. Experimental data are also presented for the apparent particle radius as a function of the local oscillator level, and are compared with theoretical predictions.