Z-SCAN MEASUREMENTS OF PHOTOREFRACTIVE NONLINEARITIES FOR A SBN-CE CRYSTAL

In this paper, we derived the Z-scan formula for a photorefractive cry stal sample under an external applied electric field. The far-field di ffraction pattern of a Gaussian beam wavefront through a photorefracti ve crystal is calculated by considering spatial-phase perturbation ind uced by the space-charge field. The photorefractive drift nonlineariti es and correspondingly, the electro-optic coefficients r(33), r(13), ( r(23)) and the characteristic ratio n(e)(3)r(33)/n(0)(3)r(13) for a ce rium-doped Sr0.61Ba0.39Nb2O6 crystal are determined from the Z-scan ex periments; Z-scan with enhanced sensitivity is also realized by measur ing the normalized transmittance at the off-axis position in the far f ield. A deviation between the off-axis Z-scan experimental results and the theoretical prediction is discussed too.