Simple optical method for determination of crystal orientation in photorefractive crystals.

A simple optical method for determination of crystallographic orientations +/-x, +/-y, and +/-z in photorefractive crystals based on light amplification via backward two-wave mixing (TWM) is presented. We consider a photorefractive Fe-doped lithium niobate crystal (LiNbO(3):Fe) with a standard x-y-z cut as an example to illustrate the principle, manipulation, and experimental results of this method in detail. Also we see that the direction of the light amplification, namely, the direction of the nonreciprocal steady-state energy transfer, strongly depends on the direction of the grating vector with respect to the corresponding crystallographic axes mainly under the diffusion mechanism. Finally, a way of determining the sign of the charge carriers in photorefractive materials is proposed.