摘要:
研究了CO2激光局域辐照对熔石英损伤特性的影响,发现当辐照中心温度较低时(1139 K),辐照对损伤阈值没有明显影响,但辐照中心温度较高时(1638 K),辐照对损伤阈值有明显的影响,损伤阈值随距离辐照中心间距的增大而减小,在残余应力产生光程差最大处附近,损伤阈值降到最小,随着与辐照中心间距的进一步增加,损伤阈值略有上升.对导致此现象的原因做了分析.由于残余应力的存在,在辐照中心发生再损伤产生的裂纹后,裂纹先沿径向扩展,在残余应力产生光程差最大处附近,裂纹转而向切向扩展,这可能与径向和环向张应力随半径的变化有关.在采用热处理炉退火消除残余应力时,必须注意元件的洁净处理,否则退火会出现析晶现象,对损伤阈值和透射率造成不良影响.
Abstract:
The influence of CO2 laser local irradiation (CLLI) on the laser damage resistance of fused silica was studied. It is found that CLLI has no evident effect on the laser-induced damage threshold (LIDT) of fused silica when the temperature of irradiation center is low (1139 K). However, the influence of CLLI on LIDT becomes important when the temperature of irradiation center is higher (1638 K). AT first, LIDT decreases with r increasing from zero to rM, where r is the distance to irradiation center, and rM is the distance at which the residual stress-induced phase retardance reaches the maximum. Then, LIDT increases a little when r is larger than rM. The origin of this phenomenon is discussed. Due to the residual stress, re-initiated damage in irradiation region can result in the formation of fractures. The fractures due to the re-initiated damage at irradiation center transport along radial direction firstly, and then transport along the tangential direction near rM. This may be due to the maximum tensile hoop stress and radial stress dependence of radius. Cares should be taken for the optical cleaning when thermal oven annealing is used to eliminate the residual stress. Otherwise, crystallization can be induced by contamination during annealing. The contamination also has negative impact on the light transmission and LIDT.
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