经过理论推导,分析了320 mm口径衍射光学元件在束匀滑实验中光强分布出现高级次衍射斑和元件实际衍射效率变低的原因,模拟计算得到了接近实验的光强分布。模拟分析发现:通过调整设计参数,如适当增加抽样点数,使设计时焦斑主瓣占输出计算窗口的比例减小至0.2以下,可以大大降低由于高级次衍射斑造成的衍射效率损失,控制在2%以内,使台阶分布式相位片实际衍射效率得到提高,在对口径为70及320 mm的台阶分布式相位片样品测试中得到了验证。

The reason is theoretically discussed for the existence of sub-diffractive spots around the focal spot and the decrease of diffraction efficiency in beam smoothing by 320 mm-diameter diffractive optical elements. Through the simulation analysis,it is suggested that,by means of adjusting the design parameters,the intensity of sub-diffractive spots can be suppressed effectively,which can ensure the effect of diffractive optical elements in beam smoothing. For example,by appropriately increasing sampling points,the proportion of focal spot to whole output range,named Yita,can be decreased,and the efficiency loss engendered by sub-diffractive spots would be restricted. When Yita is less than 0.2,the efficiency loss can be controlled within 2%. The experimental results with 70 mm- and 320 mm-diameter distributed phase plates have validated the simulation results.