Multiangle light scattering

Abstract: A photoelectric apparatus for the measurement of the angular dependence of light scattering from solutions is described in detail and its performance is discussed. Methods of calculation for the determination of the average extension of the scattering molecules from the data are described. Data are presented for two fractions of polystyrene in various solvents, showing the effect of changing solvent power and temperature, and also confirming a theoretically derived formula for the concentration dependence of the scattering.

Abstract: A HeNe laser beam incident on a sample of micron-sized spheres suspended in water scatters into a random pattern of spots of varying size, shape, and intensity. The pattern results from the coherent superposition of the outgoing waves scattered from the spheres. Because the spheres are in constant Brownian motion, the pattern randomly changes in time. A photodetector is placed in the pattern and the random fluctuations in the light intensity are measured and analyzed. The signal’s autocorrelation function and power spectrum are computed and used to verify the Brownian motion and determine the spheres’ diameter.