Study On Growth And Properties Of Large Size Nd,Ce: YAG And Mid Infrared Er: YAG Laser Crystals

At present,the rapid development of high-power solid-state laser technology has led to the development of high-quality,large-size laser crystals and has become a research hotspot.The commonly used Nd:YAG crystal is limited by the position and width of the absorption band,and the energy utilization of short wavelength pump light is not high.In addition,the segregation coefficient of Nd³⁺in YAG is very low(about 0.2),and it also limits the improvement of laser efficiency.A new laser crystal material with large-size and high conversion efficiency needs to be developed.In recent years,with the application of laser in remote sensing,coherent radar,optical detection and space optical communication,the safety of human eyes is 1.50?1.67?m.The demand for laser band is increasing,and the demand for lasers with large transmission distance,high power,high pulse energy and good beam quailty is increasing.Among the many activated ions,Er³⁺produces 1.5?1.67?m because of its~4I_13/2-~4I_15/2transition band laser is the most valuable and potential near-infrared laser activated ion.Among the many Er³⁺doped laser crystals,Er:YAG crystals have been the most widely studied and applied due to their excellent physical and chemical properties,but there are still many problems in the preparation of large-sized,high-concentration Er ion-doped YAG crystals.Technical barriers,relatively few studies on high-quality Er:YAG crystals.Based on the above background,in this work,Large-size Nd,Ce:YAG and mid infrared Er:YAG laser crystals were prepared by medium frequency induction heating Czochralski method.The growth conditions,defects,spectra and laser properties of the crystals were systematically studied.The specific work is mainly as follows:1.Growth of Nd,Ce:YAG laser crystals.High-quality Nd,Ce:YAG crystals with a diameter of 50 mm are prepared by medium frequency induction Czochralski method.The formation of cracks and inclusions in the crystal growth process was successfully overcome by improving the temperature field environment and process parameters.The powder diffraction pattern of Nd,Ce:YAG crystal is basically consistent with the XRD pattern of standard YAG crystal,and the YAG lattice distortion caused by doped nd and Ce ions is relatively small.2.Er:YAG crystal growth.High quality large-size Er:YAG single crystals with a diameter of 40 mm and a length of 150 mm were prepared by Czochralski method.The X-ray diffraction pattern shows that it has good phase purity,and the introduction of Er has no effect on the matrix structure.3.Study on defects of Nd,Ce:YAG crystals.The causes of inclusions and cracking defects in the growth of large-size Nd,Ce:YAG laser crystals are analyzed from the combination of theory and practice.The results show that the inclusion defects in Nd,Ce:YAG crystals are mainly caused by component supercooling.The generation of inclusion can be inhibited by increasing the temperature gradient of growth interface and variable speed growth process;The cracking defect during shoulder placement is mainly caused by the excessive temperature gradient of the upper insulation system.The existence of multi-layer insulating structure can effectively reduce the probability of crystal cracking structure.The cracking problem caused by crystal cooling can be solved by using multi-stage slow cooling procedure.4.Optical properties of Nd,Ce:YAG crystals were studied.The absorption spectra of Nd,Ce:YAG crystals have absorption peaks corresponding to Nd:YAG crystals,and strong absorption bands at 370nm and 460nm,which is due to the 4f-5d2 and 4f-5d1transitions of Ce³⁺.Compared with Nd:YAG crystal,Nd,Ce:YAG crystal has strong near-infrared emission at 1066nm under 370nm and 460nm excitation,which is due to the energy transfer from Ce³⁺to Nd³⁺.The results show that the energy transfer from Ce³⁺to Nd³⁺is mainly composed of non radiation and radiation.The doped crystal structure can significantly reduce the laser threshold and make more full use of the pump energy and laser output energy.In addition,the laser threshold is also significantly reduced.The results show that Ce³⁺doped into YAG crystal has a good sensitization effect on Nd³⁺.We expect that double doped Nd,Ce:YAG crystals will play an important role in the manufacture of high-energy and miniaturized solid-state lasers.5.Study on optical properties of Er:YAG crystal.(1)By measuring the absorption spectrum of Er:YAG crystal,it is found that there is strong absorption at about 380nm(~4I_15/2?~4G_11/2)and 523nm(~4I_15/2?~2H_11/2),and it is consistent with the excitation peak position obtained from the excitation spectrum;Among the ~4I_11/2energy levels in the 940-1030nm band,the absorption at 967.5nm band is the strongest,which is very suitable for the mature 940-970nm LD pump source.(2)The fluorescence spectra of Er:YAG crystal.Under the excitation of 380nm and523nm,the main emission peak of the crystal was about 1528nm(~4I_13/2?~4I_15/2);The ~4I_11/2-~4I_15/2transition of Er³⁺was studied under 970 nm excitation1.50-1.67?m.There are four strong emission peaks in the M-band range:1516nm,1533nm,1573nm and 1620nm.(3)The fluorescence decay curves of YAG:Er single crystal were obtained by monitoring 380nm and 1528nm,and its lifetime was calculated to be about 4.56ms.