By reducing the working temperature of opto-mechanical structures, the infrared system signal to noise ration can be effectively improved. Normally, structures close to the focal plane radiate more noise. Signal to noise ration can be improved by cooling the opto-mechanical in front of the focal plane. In this paper, an infrared lens working at both room and low temperature is designed. The first four lenses work at room temperature and the other three lenses close to the focal plane work at 200K. The cryogenic lens is cooled by space pulse tube cryocooler. UG TMG thermal analysis results show that the working temperature of each lens meets the requirements, and the temperature gradient of each lens is less than 0.2K. Modal analysis results show that the first modal frequency is 97.2Hz. The finite element analysis results show that the maximum stress of the structure is 227.8MPa, which is far less than the allowable stress of TC4. Thermal-structure-optical analysis show that the system MTF has a small decrease from root temperature to working temperature. By adjusting the position of the focal plane, the system MTF can recover to the design results. The results of the vacuum experiment show that the working temperature of the lens is close to the simulation results. The wavefront error is measured both at room temperature and working temperature. The average wavefront error is 0.060λ (λ=632.8nm) at working temperature and 0.070λ at room temperature. Experiment results verify the correctness of the thermal design and opto-mechanical design.
A depolarizer is usually used to reduce the polarization response of the spectrometer. On the basis of LYOT depolarizer, a depolarizer composed of two quartz crystals with the same wedge angle is designed and developed. Based on the matrix optics theory, this paper studies the relationship between the residual polarization degree of a LYOT depolarizer and the polarization angle of incident light, wavelength, spectral bandwidth, crystal central thickness. The residual polarization degree of a LYOT depolarizer is tested on the polarization sensitivity tester, and the test results are in good agreement with the theoretical analysis results. The LYOT quartz depolarizer can meet the requirements of spectral radiation measurement, and is of strong engineering practice.
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