Enhanced photorefractive performance of bulk cu-doped KNSBN crystals through surface electrostatic modification

The remarkable photorefractivity enhancement was observed and investigated in copper-doped (K0.5Na0.5)0.2(Sr0.75Ba0.25)0.9Nb2O6 (Cu:KNSBN) crystals due to charge accumulation on the surface, stemming from electrostrictive effect. This electrostatic modification to the surface was studied with conventional two beam coupling experiment and over 17 high diffraction orders were observed. To estimate the amount of charge accumulation, the surface charge density was measured through direct current measurement using a close loop circuit. It was believed that a thin phase grating was responsible for the diffraction pattern, which was confirmed by the related reading experiment. Corresponding calculation and analysis were given to highlight the strong refractive index modulation of the gratings.