COPPER-ION POINT-DEFECTS IN THE PHOTOREFRACTIVE MATERIAL (KXNA1-X)0.4(SRYBA1-Y)0.8NB2O6

We show that Cu ions doped in (KxNa1-x)0.4(SrBa1-y)0.8Nb2O6 (KNSBN) fo rm two energy levels in the band gap, which increase the effective cha rge-combination-center concentration N(eff). The two-wave coupling gai n and the response speed of KNSBN crystals are increased while the pho toconductivity and the effects of a dc field on the photorefractive pr operties are reduced. Self-pumped phase conjugation (SPPC) experiments have revealed that the effects of Cu ions on the photorefractive prop erties have a wavelength dependence. The SPPC response time at the e-1 level can be shortened to 200 ms.