The light diffraction properties of a shorter periodical domain, which is caused by an elastic wave propagating along one of two glass plates composing a liquid crystal cell, are described. The shorter periodical domain is controllable for the application of an electric field to the liquid crystal cell. The response time of the disappearance of the shot-ter periodical domain decreases with increasing the applied voltage, On the other hand, the response time of the domain formation is independent of the applied voltage. These response times agree quantitatively with those of the birefringence electrooptic effect. The domain disappearance by applying the voltage to the liquid crystal indicates the Freedericksz transition.