Research Of Preparation And Holographic Storage Of Hf:Fe:Cu:LiNbO₃ Crystal

In this paper,the Czochralski method was used to grow different [Li]/[Nb] ratios（[Li]/[Nb]=0.946,1.05,1.20 and 1.38）and Hf⁴⁺ ions doping concentrations（2,4,6 and 8 mol%）in the Hf:Fe:Cu:LiNbO₃ crystals.The grown crystals are subjected to polarization,orientation,cutting,polishing,etc.to obtain samples that meet the test requirements.First of all,the concentrations of Hf⁴⁺,Fe³⁺ and Cu²⁺ in all samples were determined by inductively coupled plasma atomic emission spectrometry（ICP-AES）,which shows the relationship of ion arrangement with the change of Hf⁴⁺ concentrations and [Li]/[Nb] ratios.According to the data,the effective segregation coefficient of Hf⁴⁺ decreases,but the effective segregation coefficient of Fe³⁺ and Cu²⁺ decreases gradually with the increase of Hf⁴⁺ ions concentration.The effective segregation coefficient of Hf⁴⁺ decreases and the effective segregation coefficient of Fe³⁺ and Cu²⁺ increases gradually when the [Li]/[Nb] ratio is changed.The defect structure and ion arrangement of Hf:Fe:Cu:Li NbO₃ crystals were tested by infrared absorption spectroscopy.The result shows that Hf⁴⁺ ions enter the crystals lattices from occupy Hf_Li³⁺,When Hf⁴⁺ ions enter the crystals lattices above the threshold concentration,Hf⁴⁺ ions enters crystals to replace normal Nb site to form NbHf-.When the [Li]/[Nb] ratio increases,the concentration of intrinsic defects decreases.Hf:Fe:Cu:LiNbO₃ crystals are near-stoichiometry crystal when the [Li]/[Nb] ratio reaches 1.20.The optical homogeneity of Hf:Fe:Cu:LiNbO₃ crystals was detected by the birefringence gradient,the results demonstrated that the optical homogeneity is getting better with the increase of the Hf⁴⁺ doping concentration and [Li]/[Nb] ratio.The two-wave coupling experiments was used to test the photorefractive properties of Hf:Fe:Cu:LiNbO₃ crystals with different ratios and Hf⁴⁺ ions doping concentrations.The test shows that increasing Hf⁴⁺ ions doping concentrations and [Li]/[Nb] ratio can improve the holographic storage properties of Hf:Fe:Cu:LiNbO₃ crystals.And the experiment shows that increasing the concentrations of Hf⁴⁺ and Li⁺ ions do not change photo-excited carriers excitation in Hf:Fe:Cu:LiNbO₃ crystals.The incident exposure energy method was used to test the light-induced scattering in Hf:Fe:Cu:LiNbO₃ crystals.When the doping concentrations of Hf⁴⁺ ions attain 8mol%,the exposure energy increase to 730.95 J/cm² in Hf:Fe:Cu:Li NbO₃ crystals,which is 121.4 times than HfFeCu₂.And the exposure energy attained 892.51 J/cm² in the sample HfFeCu_1.38.which is 161.56 J/cm² larger than Hf（8 mol%）:Fe:Cu:LiNbO₃ crystals.The result shows that the Hf:Fe:Cu:LiNbO₃ crystal is an ideal holographic storage.