Measuring vibration amplitudes in the picometer range using moving light gratings in photoconductive GaAs:Cr.

We report the measurements of picometer vibration amplitudes produced by a piezo mirror in an interferometric setup, using a GaAs:Cr photoconductive device. The moving light fringes (gratings) induce in this new detector periodic photocurrents characterized by efficient suppression of the low-frequency drifts of the working point and low sensitivity to the amplitude laser noise. The optimum operation conditions of this system are also shown.