Experimental confirmation of nonequilibrium steady-state theory: Brillouin scattering in a temperature gradient

The present results confirm the existence of the Brillouin intensity asymmetry induced by a thermal gradient both in a liquid (water) and, for the first time, in a solid (fused quartz). This provides a direct check of the statistical methods used in nonequilibrium physics. For water, the data show excellent agreement with linear theory. Finite size effects are clearly evident and it is suggested that wall effects are more important than mode-coupling nonlinearities.