| Laser crystals with high homogeneity and large size is the important basis to develop the high-power solid state laser,and the laser crystals with high-efficiency and anti-irradiation are desired in the space laser.The efficient segregation coefficient of Nd3+ in GSAG is about three times that of Nd3+ in YAG,and its melting point is lower than that of YAG,and it is promising to obtain crystal samples with high uniformity and large size.Meanwhile,its structure and performance is similar to Cr,Nd:GGSG which owns excellent anti-irradiation performance.Hence,in order to explore laser crystals with large size,high uniformity and good irradiation performance,Nd and Nd,Cr doped GSAG were chosen and studied.The main contents and results of this dissertation are as follows,(1)A Nd:GSAG crystal was grown successfully by Czochralski method with diameter of 30mm.The effective segregation coefficient of Nd3+ in GSAG was measured,and the structure parameter of Nd:GSAG was obtained by Rietveld refinement to X-ray diffraction data.Absorption and fluorescence of Nd:GSAG at room temperature were studied.The effective segregation coefficient of Nd3+ in GSAG is 0.53.The strongest absorption peak is located at 808.6nm and the absorption cross section at 808.6nm is 3.44×10-20 cm.The transition strength parameters ?t(t=2,4,6)were determined to be 0.263,3.010 and 3.648 in 10-20cm2.Its strongest emission peak locates at 1060nm.The stimulated emission cross sections at 1060nm and 941.5nm are 6.32×10-20cm2 and 2.77×10-20cm2,respectively.The corresponding fluorescence lifetime of laser upper level 4F3/2 is 258?s.The 1060nm laser performance of Nd:GSAG crystal was studied with a sample of 2×2×6mm pumped by 808nm LD in the continuous-wave mode,whose threshold power is 2.139W,maximum output power is 0.462W,and the corresponding slope efficiency is 8.9%and optical-to-optical conversion efficiency 5.12%.Besides,the thermal diffusion coefficient of Nd:GSAG from 297K to 748K was measured.The thermal conductivity varies from 4.51 W/(m · K)to 2.80W/(m · K)within this temperature range.(2)The Cr3+ with atomic concentration 0.1 percent were doped into Nd:GSAG.Thus a Cr,Nd:GSAG crystal of ?30mm was grown successfully by Czochralski method.The strongest absorption peak of Cr,Nd:GSAG locates at 808.6nm and the absorption cross section is 3.38×10-20cm2.Omitting the absorption bands of Nd3+ ion overlapping with that of Cr3+ ion in Cr,Nd:GSAG,the intensity parameters?t(t=2,4,6)of Nd3+ were fitted to be 0.380,2.286 and 3.306 in 10"20cm2.The strongest emission peak of Cr,Nd:GSAG crystal locates at 1060nm.The stimulated emission cross section at 1060nm and 941.5nm are 5.98×10-20cm2 and 2.6×10-20cm2,respectively.The fluorescence lifetime of the level 4F3/2 at room temperature is 274?s.The 1060nm laser performance of Nd:GSAG crystal was studied with a sample of 2x2x6mm pumped by 808nm LD in the continuous-wave mode.The threshold power is 1.233W,maximum output power is 0.513 W,corresponding slope efficiency and optical-to-optical conversion efficiency are 6.73%,5.78%,respectively.(3)Nd:GSAG and Cr,Nd:GSAG crystal were irradiated by 60Co gamma-ray sources with three different doses of 2Mrad,lOMrad and 20Mrad.Their absorption and photoluminescence were compared with non-irradiated crystal samples,which indicates that Nd:GSAG and Cr,Nd:GSAG crystal may be radiation-resistant,and Cr3+ doping is beneficial to enhance the radiation-resistant performance of Nd:GSAG. |
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