Two-wave mixing in a Ce:KNSBN crystal with incoherent erasing technique

Two-wave mixing properties of a Ce:KNSBN photorefractive crystal, is experimentally studied while the incoherent erasing technique is applied. As the signal beam is with extraordinary polarization and the polarized direction of the pump beam has an angle phi with its extraordinarily polarized direction, the gain of the signal beam is measured with respect to the angle phi. Because of the erasing of the fanning by the ordinary component of the pump beam, the gain enhances at small angle phi and obtains its maximum at phi=30% The couple-wave theory with considering of the fanning effect is used to fit the experimental data and the fitting curve is coincident with the experimental data very well. The calculated results of the gain as a function of the angle phi for different fanning factor are given out. Finally the enhancement of the gain is experimentally measured with respect to the angle between the signal beam and the normal of the crystal face. While this angle takes theta=11degrees, the enhancement of the gain obtains its minimum value, which means the minimum fanning.