Giant increase of photorefractive effect in lithium niobate: a new approach

A new approach for obtaining in short time highly efficient photorefractive holographic gratings in lithium niobate is presented. The method consists in decreasing the sample conductivity by cooling it down to liquid nitrogen temperature. In this way the initial slope of the writing curve is largely amplified, which makes possible to achieve in short time diffraction efficiencies one order of magnitude larger than at room temperature in the same conditions. Simple theoretical estimates show that in this way, provided that the proper experimental conditions are met, unit efficiency should be reachable in times much shorter than typical ones.