An effort to expand light-scattering autocorrelation techniques to Brownian diffusional and critical fluid systems in which multiple scattering effects are important, and to understand the observed similarity of the Rayleigh linewidth of light scattered from these two seemingly different systems is discussed. A formalism was developed to find the light field multiply scattered from a suspension of Brownian diffusing particles. For the field doubly scattered from a system of noninteracting Brownian particles, the intensity and correlation time were much less dependent on the scattering angle than for the singly scattered component. The polarized and depolarized correlation times of light scattered from Brownian particle systems were measured. The double-scattering formalism was extended to light scattered from critical fluid systems. In the region k xi greater than 5 the doubly and singly scattered correlation times were nearly equal. The dynamic droplet model of critical phenomena was developed which gives the proper, experimentally verified, forms for the intensity and linewidth of light scattered from a critical fluid. To test the dynamic droplet model and the mode theories Rayleigh linewidth predictions, light-scattering measurements were performed on the critical fluid system methanol and cyclohexane. The data agreed with both the dynamic droplet and decoupled mode theory predictions. The depolarized scattered spectra from a critical fluid were measured, and qualitative agreement with the double-scattering theory was found. 57 figures, 5 tables.

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We have extended the theoretical description of the lattice excitations in crystals formed of charged colloidal particle suspensions (CCPS) to include the effects of bounding surfaces. One of the new features that arises in a CCPS crystal confined by surfaces to form a film, is that propagating lattice waves cannot exist at the center of the Brillouin zone. Techniques have been developed to form systems of colloidal particles in monolayers on a water surface and on membranes. Transitions from gas to liquid to two dimensional solid phases have been observed in both classes of system. The two dimensional solid phases range from single crystals having a hexagonal lattice with long range translational order, to hexatic forms with short range translational order and long range orientation order, to amorphous or glass-like of /sub 2,6/lutidine + water have been extended to a film of thickness 0.5 .mu.m. The dynamical critical behavior of this film remains strictly three dimensional to within 2 mK of the extrapolated critical point, where an apparent first order transition occurs.