环境温度的变化会引起光学系统产生热离焦现象,导致系统像质不稳定。由于材料的限制,在深紫外波段内,光学系统的无热化设计过程和结果十分复杂。因此,提出了拆分设计和单层衍射光学元件相结合的方法实现深紫外光学系统的无热化设计。该方法首先求解了消热差、消色差方程组,并用结果对深紫外光学系统进行拆分再组合,简化了无热化设计过程。然后在组合系统中加入单层衍射光学元件以简化设计结果。用该方法对焦距为110 mm,F数为3.5,温度为-60~100 ℃的深紫外侦察相机镜头进行无热化设计,得到的系统在奈奎斯特频率为18.5 lp/mm处,调制传递函数均大于0.65。结果表明,该方法能解决深紫外透射式光学系统在宽温度范围内的热离焦问题,同时能提升系统的光学性能。

The changes in ambient temperature will cause thermal focus shift in the optical system, which leads to the instability of the image quality. Due to the limitation of materials, the athermal design process and results of optical system in deep ultraviolet band are very complex. Therefore, we propose a method combining split design and single-layer diffractive optical element to realize the athermal design of deep ultraviolet optical system. In this method, the solution of the athermalized and achromatic equations are first presented, and the results are used to split and recombine the deep ultraviolet optical system, which simplifies the athermal design process. Then a single layer diffractive optical element is added to the combined system to simplify the design results. With this method, a deep ultraviolet reconnaissance camera lens with a focal length of 110 mm, an F-number of 3.5, and a temperature of -60--100 ℃ is designed athermally. When the Nyquist frequency of the obtained system is 18.5 lp/mm, the modulation transfer functions are all greater than 0.65. The results show that this method can solve the thermal defocusing of the deep ultraviolet transmission optical system in a wide temperature range, and at the same time can improve the optical performance of the system.