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.