退火对电子束热蒸发193nm Al_2O_3/MgF_2反射膜性能的影响

Effects of annealing on electron-beam evaporated 193nm Al_2O_3/MgF_2 HR mirrors

设计并镀制了193nm Al2O3/MgF2反射膜,对它们在空气中分别进行了250—400℃的高温退火,测量了样品的透射率光谱曲线和绝对反射率光谱曲线.发现样品在高反射区的总的光学损耗随退火温度的升高而下降,而后趋于饱和.采用总积分散射的方法对样品在不同退火温度下的散射损耗进行了分析,发现随着退火温度的升高散射损耗有所增加.因此,总的光学损耗的下降是由于吸收损耗而不是散射损耗起主导作用.对Al2O3材料的单层膜进行了同等条件的退火处理,由它们光学性能的变化推导出它们的折射率和消光系数的变化,从而解释了相应的多层膜光学性能变化的原因.反射膜的反射率在优化联系、镀膜工艺与退火工艺的基础上达98%以上.

193nm Al203/MgF2 HR mirrors were designed and deposited by electron-beam evaporation, and then annealed in air at different temperatures from 250℃ to 400℃. The center wavelength shifted to shorter wavelength after annealing. And the reflectance of HR region increased but the transmittance changed negligibly little with the increasing of the annealing temperature. The total integrated scattering was measured to distinguish the scattering loss and the absorption loss. The results indicated that the total optical loss in the HR region was absorption dominant rather than scattering dominant. To know clearly the loss-reduction mechanism of annealing, the corresponding single-layers of Al2O3 were deposited and annealed in the same way. The change of optical constants was analyzed to explain the reduction of the total optical loss. And the reflectance of the HR mirrors reached was higher than 98 %.