Simple measurement of space-charge field in a LiNbO 3 crystal doped with 0.65 mol.% MgO using second harmonic generation

Abstract

We present a novel method for measuring the electric space-charge field in a photorefractive crystal by utilizing the electric field dependence of the second harmonic generation. In our experiment, a LiNbO 3 crystal with 0.65 mol.% MgO doping was used because it has the advantage that a noncritical phase matching for the second harmonic generation of 532 nm radiation is possible at room temperature. We have found that our method offers a simple measurement of the space-charge field with a similar sensitivity, compared to the conventional one in which the space-charge field was evaluated by measuring a light-induced birefringence change. The photovoltaic coefficient and conductivity could be determined by analyzing the observed relaxation behavior of the space-charge field at two different light intensities.