考虑固体热容激光器对工作介质的要求,对比分析了掺钕的玻璃、YAG和GGG的多种材料性能.并对三者在激光工作周期内的瞬态温度场及热应力进行了数值模拟.结果表明:在给定的边界及工作条件下,当钕玻璃激光器以热容方式工作,时间为5 s时,介质最高升温超过400 K,最大热致应力为25 MPa,接近其断裂极限的50%.在此条件下进行冷却,当水温为283 K时,需经过约120 s才基本恢复到初始工作状态.而Nd:YAG和Nd:GGG两种介质在相同输入工作条件下,工作时间可达10 s,且温度分布相对平坦,温差和热应力较小,经水冷约30 s可恢复到初始状态.但模拟计算中,发现Nd:YAG在冷却阶段的最大应力达77 MPa,已超过断裂阈值下限值的50%.兼顾冷却时间、材料所能承受的应力及晶体生长尺寸,以及实现100 kW的平均功率输出等因素,Nd:GGG晶体是目前三者中比较适合于作为高平均功率、重复率热容方式工作的激光材料.

Considering some necessary factors in the design of SSHCL, material properties of Nd doped glass, YAG and GGG were compared. Transient temperature fields and thermal stress in these slab mediums during one working cycle were simulated. Numerical analysis results showed that the internal external temperature difference in a neodymium doped glass slab was 75 K and the peak temperature value was 400 K when pumping time arrived 5 s. The maximum stress came to 50% of glass fracture limit. During subsequent water cooling period, the initial state was recovered after 120 s. On the same boundary conditions, Nd:YAG and Nd:GGG slabs could maintain relatively smooth temperature profile while the temperature rising and equivalent thermal stress were lower compared to glass. In later cooling phase, both of them could reach their operating commencement within 30 s. As cooling, the maximum stress of Nd:YAG overran 50% of the stress limit, thus increasing its tendency to fracture. Taken cooling time, fracture limit and obtainable size of the crystal into account, Nd:GGG should be the suitable active medium for high average power, repetitive frequency heat capacity laser.