Robert W. Gammon

Professor
Optical Physics

Light passing through materials is scattered by the thermal fluctuations in positions of the atoms. The wavelength dependence of this scattering leads to the blue color of the sunlit sky. What is less familiar is that the dynamics of the atomic motions can be measured by studying the spectrum of the scattered light. Professor Gammon and his students have been studying the internal motions of materials near critical phase transitions using techniques of laser light scattering spectroscopy. Fluids at the liquid-vapor critical point develop strong density profiles on earth due to gravity. A microgravity experiment was successfully proposed by the group. They received the prime contract to build and operate a photon-correlation, light scattering experiment. The experiment is named Zeno and measured the critical fluctuation space-time correlation functions of a xenon sample in orbit on the Space Shuttle, where the residual gravitational acceleration was a few micro-g's. The experiment flew twice, in 1994 and 1996. At the present time the publications from the experiment and its apparatus development are being prepared. The archival data set presentation together with a first analysis of the scaling of the transport coefficients (thermal conductivity and viscosity) will be the primary publication from this work. New work centers around experiments to test new ideas about microscopic chaos and to study cross-over of critical phenomena in systems in which there are competing length scales.

Selected publications:

1. Equilibration near the liquid-vapor critical point in microgravity, R. Allen Wilkinson, G.A. Zimmerli, Hong Hao, Michael R. Moldover, Robert F. Berg, William L. Johnson, Richard A. Ferrell, Robert W. Gammon, Phys. Rev. E 57, 436-447 (1998).
2. Experimental Evidence for Microscopic Chaos, P. Gaspard, M.E. Briggs, M.K. Francis, J.V. Sengers, R.W. Gammon, J.R. Dorfman, R.V. Calabrese, Nature 394, 865-868 (1998).
3. Concentration Fluctuations in a Polymer Solution under a Temperature Gradient, W.B. Li, K.J. Zhang, J.V. Sengers, R.W. Gammon, and J.M. Ortiz de Zarates, Phys. Rev. Lett. 81, 5580 (1998).

Graph of the scattering intensity as the critical point is crossed comparing data from flight with data at one g (ground): transition is very sharp in low gravity.