Density grating acoustic

Time scale for observation The response of the acoustic effect is limited by the acoustic propagation between the fringe distance and that time constant is rac = A/v. Therefore, in 0 < t rac, the density contribution is small and fast response of the population grating can be easily observed (although the Temp.G signal could contribute to the signal even in this time scale). In principle, even rather slow dynamics of the population, which is not disturbed by the thermal... 

In the experiment with the smectic-A liquid ciystal, the dominant contribution to the grating diffraction seems to come from the density effect. The observed acoustic velocity and attenuation time are in accordance with theoretical expectation. An interesting effect reported in the work by Khoo and Normandin is the formation of permanent gratings by intense excitation pulses. These gratings are erasable by... 

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