Study On Light-induced Scattering In Lithium Niobate Crystals

Lithium niobate,LiNbO₃?LN?,is one of promising optical materials with electro-optic effect,piezoelectric effect,nonlinear optics and photorefractive effect and with the reputation of“optical silicon”.And it is widely used in holographic storage,composite filter synthesis,optical waveguide devices,frequency conversion devices and Q-switch and so on.Light-induced scattering,accompanying by the photorefractive effect,which can be useful in self/mutually-pumped phase conjugator,optical limiting devices and bistable optical devices.However,it is an unwanted but inevitable side effect in holographic storage leading to graphic distortion and poor data quality,as well as in frequency conversion devices and Q-switch.Therefore,we need study the factors that influence the light-induced scattering behavior of LiNbO3 to take effective measures to regulate light-induced scattering.In this paper,we study the light-induced scattering behavior of LiNbO₃ under various parameters.Firstly,we study the temperature dependence of the temporal evolution of light-induced scattering in y-cut congruent,Hf-codoped and near-stoichiometric LiNbO₃:Fe crystals.We systematically measure the light-induced scattering curves of LiNbO₃:Fe with different Hf-doping and the Li components at varied temperatures ranging from 20 to 200^°C,as well as the“liquid nitrogen temperature”in congruent LiNbO₃:Fe crystal.Moreover,we analysis the experiment results in detail and fit the scattering curves.Basing the saturation refractive-index modulation,the partial self-recovery process and temporal evolution are explained by the slow recombination of light-induced space charges of the noise gratings with high wave vectors.Basing the recombination and rebuild of charge carriers at the surface or near the crystal surface through the surface conductivity,the anomalous spikes appear in the partial self-recovery process in congruent LiNbO₃:Fe crystal is well explained.Basing the the activated protons at 85^°C and proton concentrations difference,the“scattering acceleration effect”is explained by their impact on the photoconductivity.In both Hf-codoped congruent and near-stoichiometric LiNbO₃:Fe crystals.And the low concentration of protons in near-stoichiometric SLN:Fe crystal is suggested to account for the relationship between the pump-intensity and“scattering acceleration effect”.Secondly,the influence of pump intensity and polarization on the light-induced scattering of LiNbO₃ crystals are studied.In general,with the increasing pump intensity,both photorefractive effect and light-induced scattering accompanying by the photorefractive effect usually become serious.At liquid nitrogen temperature,we study the effect of e-polarized and o-polarized pump light on the scattering behavior of LiNbO3:Fe crystals.Through fitting the curves,we find the scattering curves conform to the double exponential model under the irradiation of e-polarized light while they follow Single-index model.Finally,a platform of wide-angle scanning of light-induced scattering is designed and developed.Using the set-up,we can measure the space angle distribution of scattering intensity.And PILS was utilized as a technique to measure all parameters describing the photorefractive behaviors of LN,such as photovoltaic field,the diffusion field and so on.