Chinese Journal of Lasers, Volume. 51, Issue 8, 0810005(2024)

Stray Light Analysis of Long‐Wave Infrared Refrigeration Dewar Components

Haiyong Zhu, Junlin Chen, Zhijiang Zeng*, Qinfei Xu, Xiaokun Wang, Yaran Li, and Xue Li
Author Affiliations
  • State Key Laboratory of Transducer Technology, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Shanghai 200083, China
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    Objective

    Infrared detection technology is widely used in the aerospace industry owing to its strong anti-interference capabilities and wide detection ranges. This enables comprehensive and large-scale continuous monitoring of land and oceans. Notable examples include the successful launch of the Ocean No.1 (HY-1A) and Fengyun sequence satellites, both of which are equipped with an infrared payload. However, infrared detection is challenging because of weak target signals and the need for increased detector sensitivity. To address this issue, infrared focal plane detectors such as mercury cadmium telluride (MCT) operate at lower temperatures, necessitating sufficient cooling capacity provided by refrigerators. Currently, most MCT detectors used in space applications employ mechanical refrigeration. These detectors are typically packaged in a metal Dewar to meet low-temperature working requirements and are coupled with the refrigerator through the Dewar cold finger. Hence, the Dewar design directly affects the refrigeration efficiency. Additionally, strict stray light analysis and suppression are essential for satisfying the high-performance requirements of infrared remote-sensing loads. This is crucial for ensuring the accurate quantitative inversion and image quality of infrared remote sensing data. A notable example is the temporary shutdown of the EU Meteosat-5/7 series imager owing to stray light interference. Infrared remote sensing detection systems, particularly those operating at long wavelengths, rely heavily on the suppression of internal stray light radiation to enhance image quality. To reduce the infrared component background radiation, the infrared component barrel, lens, and Dewar window are often low-temperature optically processed, ensuring the infrared optical component cooling capacity in a limited space becomes the key to component design.

    Methods

    To suppress stray light in the system, the veiling glare index (VGI) is calculated based on the functional relationship between the point source transmittance (PST) and the VGI (Fig.2). In addition, the VGI and noise signal ratio (NSR) are used as indicators to investigate methods for suppressing external stray light and background radiation. This study aims to optimize the design of a Dewar cold screen and window. Initially, the effectiveness of the cold optical design for reducing the background radiation of the system is compared (Figs.3 and 4). Refrigeration is essential for the cold optical design and proper functioning of the Dewar detector. The impact of the Dewar cold screen and window design parameters on the Dewar heat loss is examined (Tables 1 and 3). By fitting the experimental data, the relationship between the Dewar heat leakage and chiller power consumption is defined (Fig.6). Subsequently, a cold-screen design with low cooling power consumption is proposed (Fig.8), and the values of the system VGI and Dewar NSR are calculated through simulations.

    Results and Discussions

    The results indicate that the cold optical design effectively reduces stray light from background radiation in the system. The NSR of the three bands operating in the system decreases significantly from above 4.5 to below 0.35 (Fig.4). Theoretical calculations demonstrate that as the distance between the cold screen and window decreases, there is an increase in the Dewar heat leakage and power consumption of the refrigerator (Table 1). Furthermore, the relationship between the Dewar heat leakage and power consumption follows an E-exponential function (Fig.6). By utilizing the new cold-screen design (Fig.8), it is possible to reduce the power consumption of the refrigerator while simultaneously improving the external and Dewar background radiation stray lights (Figs.9 and 10).

    Conclusions

    With the improvements in the detection accuracy of space remote sensing loads, stray light suppression design has become a key technology in space remote sensing. The infrared optical load benefits from the low-temperature optical design, which effectively suppresses the background radiation of the infrared system. The refrigeration of the refrigerator is crucial for the normal operation of the detector and the low temperature optical design. Therefore, it plays a key role in ensuring an efficient stray-light-suppression design within the limited refrigeration resources of refrigerators. This study utilizes the functional relationship between the PST and VGI to calculate the VGI. It investigates the impact of the Dewar cold screen and window design on the external stray light, system background radiation, and power consumption of the refrigerator using the VGI and NSR as indicators. This study establishes a preliminary system for a Dewar cold screen and window design, encompassing stray light suppression and Dewar heat leakage designs. A cold screen design that achieves both low cooling power consumption and high stray light suppression is proposed. Under these design conditions, the Dewar heat leakage is 1.7 W, the chiller power consumption is 103.72 W, VGI is reduced from 1.95% to 1.92%, and the energy proportion of the window radiation stray light is reduced by 60%, meeting the project design requirements. This study addresses issues related to low-temperature optical design, refrigerator power consumption, and stray light suppression, providing valuable insights for the design and engineering applications of infrared Dewar refrigeration components.

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    Haiyong Zhu, Junlin Chen, Zhijiang Zeng, Qinfei Xu, Xiaokun Wang, Yaran Li, Xue Li. Stray Light Analysis of Long‐Wave Infrared Refrigeration Dewar Components[J]. Chinese Journal of Lasers, 2024, 51(8): 0810005

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    Paper Information

    Category: remote sensing and sensor

    Received: Nov. 14, 2023

    Accepted: Jan. 4, 2024

    Published Online: Apr. 11, 2024

    The Author Email: Zeng Zhijiang (jonzeng@mail.sitp.ac.cn)

    DOI:10.3788/CJL231399

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