机械制冷机冷却的透射式光学系统支撑结构

低温光学能够降低红外光学系统自身热噪声，有效提高探测灵敏度。支撑结构是实现光学系统在低温下正常工作的关键部件。设计的透射式低温光学系统工作温度为150 K，采用脉冲管制冷机这种新型机械式低温制冷机做冷源。因制冷机冷指直径较小，直接冷却光学透镜会在透镜内部产生较大温差，影响成像质量，为此设计了一种新型支撑结构，一方面设计了新型的轴向支撑和径向支撑用来减少透镜在低温下的形变，另一方面建立了透镜与脉冲管制冷机之间的传热模型，来指导支撑结构热设计，减小透镜内部温差。最后，对透镜支撑的低温性能进行了测试，实验结果表明，经过3 h，透镜温度由300 K降至150 K，支撑结构很好地保护了透镜并且在降温过程中透镜内部温差小于1 K。当温度从300 K降低到150 K时，光学表面的最大变形小于1（1=632.8 nm）。支撑结构从机械和热学性能上满足了低温光学系统的需要，为机械式制冷机冷却光学系统的光机结构设计提供了一种新选择。

Lens mount for cryogenic refractive optics cooled by mechanical cryocooler

In practical application, cryogenic optics can effectively improve the detection sensitivity by reducing the thermal noise of the infrared optical system. The lens mount is a key component to ensure the normal performance of the cryogenic optical system at cryogenic temperature. A transmission optical system was designed to work at the operation temperature of 150 K where the pulse tube cryocooler was used as a novel mechanical cryocooler to cool the optics. However, due to the small diameter of the pulse tube cryocooler's cold finger, the temperature difference within the lens was large when it was connected directly with the cold finger. So the lens needs to be cooled via a properly designed mount. Specialized axial support and radial support were designed to prevent from making damages and large distortion of the lens at cryogenic temperature. The heat transfer model between the lens and the pulse tube cryocooler was established to guide the lens mount thermal design. Finally, the cryogenic performance of the lens mount was tested. The experimental results showed that in about three hours, the optical components survived the cool-down process from the initial temperature of 300 K to the operation temperature of 150 K, and the maximum temperature difference within the lens was less than 1 K. The distortion test showed the maximum deformation of the optical surface was less than 1(1=632.8 nm) when the temperature decreased from 300 K to 150 K. The designed lens mount successfully satisfies the requirements of this cryogenic optical system which provides a new choice for the cryogenic optics cooled by mechanical cryocooler.