一种透射式低温光学系统的设计与验证

由于能够减小系统自身的热噪声和提高系统信噪比，低温光学是实现高灵敏度红外探测的必要手段。提出了一种将脉冲管制冷机用作冷源的透射式低温光学系统。这种新型低温光学系统可用于体积和重量受限而又需要进行高灵敏度红外探测的场合。从光学设计、光机结构设计和内部热噪声分析等方面说明了透射式低温光学系统的设计过程。搭建了用于对脉冲管制冷机冷却光学系统的可行性进行验证的试验系统，并从系统内部热噪声的角度对低温光学的有效性进行了验证。实验结果表明，经过3 h，透镜温度由300 K降至设计温度150 K，继续降温则可达到最低温度105 K。测试过程中，透镜保持完好，验证了将脉冲管制冷机用作冷源的可行性。用黑体和320×256元碲镉汞探测器对光学系统自身的热噪声进行了测试。结果表明，当光学系统的温度从300 K降至215 K时，其自身热辐射减少了75%。这与理论分析结果一致，验证了低温光学降噪的有效性。

Design and Verification of a Cryogenic Refractive Optics

Since cryogenic optics can reduce thermal noise and improve the signal-to-noise ratio of detection systems, it is the necessary way to implement high sensitivity infrared detection. A cryogenic refractive optics which uses a pulse tube cryocooler as its cold source is proposed. This new cryogenic optics can be used in the occasions where volume and weight are limited and high-sensitivity infrared detection is required. The design process of the cryogenic optics is described in the aspects of optical design, opto-mechanical structure design and internal thermal noise analysis. A test system for verifying the feasibility of cooling optics by pulse tube cryocoolers is built and the effectiveness of the cryogenic optics is verified in the aspect of the thermal noise in the detection system. The experimental results show that the temperature of the optical components drops to 150 K from room temperature in three hours and can further drop to the lowest temperature 105 K. In the test process, the lens is well preserved, which verifies the feasibility of using a pulse tube cryocooler as the cold source. A blackbody and a 320× 256 pixel HgCdTe array detector are used to test the thermal noise of the optical system. The results indicate that the thermal radiation is decreased by 75% when the temperature of the optical system drops from 300 K to 215 K. This is in good agreement with the theoretical analysis result. It demonstrates the effectiveness of reducing noise for cryogenic optics.