Conversion phenomenon of defocusing-contract in Cu:KNSBN crystals
Cu:KNSBN晶体中光束散焦-收缩转换现象

We have observed that a weak light beam will experience a defocusing\|contract process before it comes to steady state when passing through a Cu:KNSBN crystal with a transient spatial electric field. This process became fast by increasing intensity of the light beam. We believe that the defocusing\|contract process results from both effects of the transient electric field in the crystals and the photovoltaic and refocusing fields generated by the beam itself.