Brillouin scattering was used to study the dynamic properties of the mixed crystals (KBr), "(KCN)". By analyzing the frequencies and linewidths of the T2g-symmetry phonon, we were able to determine the cyanide quadrupolar relaxation rate as a function of temperature in the paraelastic regime. We found that this relaxation frequency is proportional to exp( -1/T), rather than proportional to the square root of temperature (&T), as assumed in Michel's random-field theory. Modifying this theory by incorporating the observed temperature dependence of the relaxation rate improves the agreement with experimental data but is still not adequate. The hierarchically constrained relaxation model of Palmer et al. , on the other hand, does provide a phenomenological explanation for our data. In addition, we have determined the value of the random-field strength in these mixed systems.

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The optical properties of area detectors used in conjunction with Fabry–Pérot interferometers are analyzed. A system using a charge-coupled device as a detector for Brillouin spectroscopy is described. With a 2 pass+2 pass tandem system the finesse ranges from 50 to 63. With a collection time of about 2.5 min, the intensity of the surface Rayleigh mode and the bulk acoustic modes of Si are comparable to those obtained by scanning for many hours.

SYNOPSISThe kinetics of sol-gel-glass transformations have been studied in the thermosets of diglycidyl ether of bisphenol A cured with diamino diphenyl methane and diamino diphenyl sulfone, at different temperatures using Brillouin light scattering. The shape of the Brillouin peak is generally broad. This is attributed to the damping of elastic waves in the mixture of unpolymerized low-molecular weight fluid and the polymer chains forming the networks. The Brillouin peak becomes sharp and narrow at complete curing of the thermosets. The phonon velocity increases and the attenuation decreases with the curing time. These changes occur in two steps with the second step appearing near the gelling time of the thermosets.A semilogarithmic plot of the time for the velocity and attenuation to reach half of their total change against the reciprocal temperature yields a straight line with different slopes for the two thermosets. It is suggested that Brillouin light scattering is a useful non-destructive, in-line, method for control in the processing of epoxy thermosets. * Current Address: Groupe #Etudes de MBtallurgie Physique et Physique des Matbriaux, UA CNRS 341, INSA, Bitiment 502, 69 621 Villeurbanne CBdex, France.

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