Photorefractivity of Hafnium-doped congruent lithium-niobate crystals

Transient and steady-state measurements of photoinduced birefringence in Hf-doped congruent lithium–niobate crystals are presented. Through a systematic investigation of crystals with different dopant concentrations, we find that Hf doping induces a progressive decrease of photorefraction up to a threshold concentration of about 4 mol %. Such a decrease is correlated to a corresponding increase in photoconductivity. The interpretation of measurements has to take into account heating effects that may be attributed to nonlinear absorption processes.