Growth And Properties Of Doped Lithium Niobate Crystals For QPCPA

Quasi-parametric chirped pulse amplification?QPCPA?is a new pulse amplification technology,which has the advantages of high conversion rate of CPA and large bandwidth of OPCPA.At present,only the YCOB crystal doped with Sm ions can be successfully used in the nonlinear optical crystal.The narrow transmittance range makes the crystal unable to meet the QPCPA amplification with wavelength over 2500nm,so more QPCPA materials for application need to be found.In this paper,different concentrations of Pr ion?0.5mol%,1mol%,2mol%?were doped into Li Nb O₃ crystal to complete the absorption of idling frequency light?1588nm?.Meanwhile,the growth of Pr:Mg:Li Nb O₃ crystal?0.5mol%Pr ion concentration,5mol%Mg ion concentration?was conducted to determine whether Mg ion-doping can improve the laser damage threshold of the crystal.The purpose is to realize the amplification output of 3000nm pulse laser by using the quasi-parametric chirped pulse amplification technology.In this paper,high purity doped Li Nb O₃ polycrystalline raw materials were synthesized by solid phase mixing method and sintering process optimization,and the growth of the designed Li Nb O₃ series crystals was successfully completed,with Czochralski method and Bridgeman method,by means of design,optimization of furnace chamber structure and improvement of growth parameters.In this paper,the phase structure,defect structure,doped ion component,Li element content,thermal properties,spectral properties and laser damage threshold of the as-grown crystals were studied.X-ray powder diffraction results showed that the phase structure of the doped Li Nb O₃ crystal did not change significantly;Through the polarization and corrosion of the crystal,the dislocation structure of the crystal can be observed;The results of ICP-OES showed that the coagulation coefficients of Pr ion and Mg ion in the crystals were close to 1 without obvious segregation;The content of Li₂O in crystal was calculated by Raman spectrum,and the results showed that the Li content of the crystal was similar to that of the congruent lithium niobate crystal;By testing the density,specific heat and thermal diffusion properties of the crystals,the thermal conductivity data of the doped crystals was calculated,and the results showed that lithium niobate had higher thermal conductivity than YCOB and LGN crystals,and had certain advantages in the application of QPCPA;The spectrum of the as-grown crystals results showed that the crystal under the excitation of 370 nm light excitation,could be in a strong emission peak at 619 nm,and the crystal has a transmittance of more than 65%at the pump light?1030nm?and signal light?3000nm?,a strong absorption peak at 1572nm with an absorption coefficient of up to 11cm^-1,which can complete the absorption of the free frequency light?1588nm?,and all meet the requirements of QPCPA on the spectral properties of the required nonlinear optical crystal;A 532nm pulsed laser with a pulse width of 10ns was used to test the optical damage resistance of the crystal,and the results showed that the as-grown crystals could withstand the energy of over 100m J from the nanosecond pulsed laser,and the threshold of the optical damage resistance of the Pr-Mg sample reached 4.74×10⁷W/cm²,showing a good ability to resist optical damage.