光学薄膜激光损伤阈值测量不确定度

光学薄膜的激光损伤阈值是评价其激光耐受性能好坏的一个重要指标。对薄膜激光损伤阈值的准确评价和测定，是判断其激光耐受性能和进行相互比对的基础。通过对激光损伤阈值测试系统误差的溯源分析和计算机模拟，给出了优化测试系统的方向。研究结果表明:在激光光斑确定的情况下，激光能量越高，能量密度的误差越大。因此在满足需要的情况下，应该尽可能选取较低的激光能量。在激光能量确定的情况下，存在一个临界光斑，当小于临界光斑时，能量密度误差变化非常剧烈，光斑越小，能量密度误差越大。测试系统的激光光斑大于临界光斑时系统的误差较小，小于临界光斑时系统的误差急剧变大。因此，在激光损伤阈值测试系统中，应该优选临界光斑或者大于临界光斑。激光损伤阈值拟合产生的最大误差为最大能级的激光能量误差，因此要尽可能降低激光器的脉冲能量。由此可见，设计合理的系统参数，可以最大程度降低测量结果的不确定度。

Measurement uncertainty of laser-induced damage threshold of the optical thin films

The laser-induced damage threshold (LIDT) of optical films is an important index for assessing the film's properties of laser tolerance. Accurate measurement for the LIDT is the foundation of laser tolerance estimation and data comparison of the thin films. Based on the analysis and computer simulation, the optimization ways of laser-induced damage threshold was presented in this paper. The results show that the error of the energy density increased with the increase of the laser energy at a fixed laser spot. Therefore, in the case of satisfying the need, it is better to choose low laser energy for the testing system. Under the fixed laser energy, there will be a critical laser spot. The error of the energy density changed strongly with the spot size change:smaller spot size, bigger energy density error. The small gentle energy density error can be obtained at the laser spot size greater than the critical laser spot, vice versa. Therefore, it is better to choose the spot size equal or greater than the critical laser spot size.The fitting maximum error is equal to that of the error of the maximum laser energy level. Thus it can be seen that the uncertainty of a LIDT test system can be reduced through designing suitable laser parameters.