| Nd:YAG crystal is the most widely used laser medium,it is the preferred laser medium for high power solid laser,which has many advantages,such as high efficiency,low threshold,good thermal and mechanical properties,etc.But its effective segregation coefficient of Nd3+ in YAG is only 0.2,which result in a great restraining factor to prepare large volume and high optical homogeneity laser crystal medium.Meanwhile,its poor radiation resistance also result in its application in space laser to some extent.Besides,high doping concentration of Nd3+ ion will cause the laser efficiency decrease,and the FWHM of the fluorescence spectral line is narrow,so it is difficult to obtain picosecond laser output.If Sc3+ ions replace Al3+ ions in YAG partly,the effective segregation coefficient will increase.In this paper,Nd:YSAG crystal was choosen as a research object,its crystal growth technique was studied,its crystal quality was detected,and the effective segregation coefficient and crystal structure were determined.Its spectral and laser properties before and after ?-irradiation were also studied.The main results are listed as following:1)The preliminary crystal growth technique of Nd:YSAG was obtained,and(1.55 at.%)Nd:YASG crystal of(?)30mm×60mm was grown by Czochralski method.The FWHM of X ray rocking curve is 0.05 degrees,which indicates that the crystal has relatively good quality.The effective segregation coefficient of Nd3+ in YSAG is 0.35,which is more favorable for the growth of high homogeneity and large size laser crystal than 0.2 in YAG.2)The stucture data of Nd:YSAG was given by Rietveld refinement.Nd:YSAG crystal belongs to the space group Ia3d,and the lattice parameters a is 12.2582 A.Nd and Y atom occupied the Wyckoff position 24c,Sc,Al and O atoms occupied Wyckoff position 16a,24d and 96h,respectively.The fractional coordinate of O atoms is(0.0302,0.0512,0.6564).3)The absorption and luminescence properties of Nd:YSAG crystal were studied.Nd:YSAG has the strongest absorption in 808.9 nm,the corresponding absorption cross section and FWHM are 1.176 ×10-19cm2 and 2.8nm,respectively.Its transition intensity parameters ?2,?4,?6 are 0.314,3.78,4.27 in 10-20 cm2,respectively.The strong emission peak from 4F3/2 to 4I9/2 and 4I11/2 is 942.6 nm and 1059nm,whose emission cross sections are 2.21 and 1.1 in 10-19cm2,respectively,and are a littile more than that of Nd:YAG,whose emission cross sections in 946nm and 1064nm are 2.07 and 0.98 in 10-19cm2?respectively.It showes that Nd:YSAG has comparable or slightly better laser performance than Nd:YAG.4)The laser opearation was realized in(1.55 at.%)Nd:YSAG crystal of 2mm X 2mm X 6mm by LD pumping,whose laser threshold is 0.85W,slope efficiency is 21.1%,and the maximum laser output of 1.1 W is obtained.5)The additional absorption loss of Nd:YSAG is very small in the range of 900nm?1500nm after the 10 Mrad ?-ray irradiation,which is about on the order of 1.0 X10-2cm-1,and the additional absorption loss is about 0.15cm-1 at 808nm.After irradiation,its level lifetime 233?s of 4F3/2 was changed to 225?s,and the laser output slope efficiency 18.6%was changed to 18%.Under the present irradiation dosage,the laser output stability of Nd:YSAG is better than that of Nd:YAG.This work indicates that the laser performance of Nd:YSAG are similar to Nd:YAG,but its lager effective segregation coefficient is more favorable for the growth of high uniformity and large size laser crystal.The laser performance of Nd:YSAG is stable after 10 Mrad irradiation,which preliminarily shows that the crystal has anti-radiation to some extent. |
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