Light scattered by a liquid crystal: a new quasi-thermal source.

The spatial and temporal coherence properties of laser light scattered by a liquid crystal cell under the application of an external dc field are studied. It is shown that the scattered field constitutes a source with very long coherence time. The coherence time can be changed by changing the value of the applied voltage, and the spatial coherence can be adjusted by varying the dimension of the illuminated spot on the cell. The effects produced when the length of correlation of fluctuations in the liquid crystal is not negligible with respect to the dimension of the spot in the cell are also studied. The scattered field is proposed as a new quasi-thermal source, alternative of the rotating ground glass disk.