Dependence of the refractive indices in LiNbO3:Cr crystals doped with HfO2

The dependence of the refractive indices, absorption edge and optical damage in congruent HfO2-doped LiNbO3 crystal are reported. A small amount of Cr3+ ions (0.1 mol%) was introduced in the doped crystals as optical probe. The experimental data indicates that the extraordinary and ordinary indices depend on the Hf4+ ions concentration showing a singularly for a dopant level of ~2.7 mol%. The dependence of the absorption edge also shows a transition region at this Hf4+ concentration. The distortion of the transmitted light through samples doped with different concentrations of Hf4+ ions indicates that an inhibition of optical damages is achieved at above 3 mol% of dopant. A charge compensation mechanism is proposed to explain the role of the Hf4+ ions for the observed experimental result.