University of Science and Technology of China Reveals High Precision Planarity Measurement of Cryogenic Arrays

Professor Wang Jian, Deputy Chief Designer of the Low Temperature Array High Precision Planeness Survey Wide Area Sky Survey Telescope (WFST) announced by the University of Science and Technology of China, and teacher of the State Key Laboratory of Nuclear Detection and Nuclear Electronics, School of Physics, University of Science and Technology of China, is a research team of the Chinese Academy of Sciences (CAS) to carry out research on key technologies of the main focus camera. The research results were published in the IEEE Journal of Instrumentation and Measurement in July 2023.

A wide field of view camera is the core equipment of a wide field of view telescope. Due to the size limitations of a single sensor, it cannot meet the needs of a wide field of view camera with a large focal plane. Therefore, the key technology for the development of large field of view cameras lies in the splicing and assembly of large target detectors. High precision focal plane arrays require precise manufacturing and measurement. Given that detectors typically operate at low temperatures to reduce dark current, measurements need to be made at room and low temperatures. This ensures that the detector maintains excellent flatness under cold conditions, thereby improving the imaging quality of the detector.

Based on the current development status of astronomy at home and abroad, combined with the development trend of astronomical technology, China fully utilizes the professional knowledge and basic research role of existing research teams. After years of preparation and accumulation, China University of Science and Technology and the Zijinshan Observatory of the Chinese Academy of Sciences jointly proposed the construction of the 2.5-meter caliber telescope WFST, which is the most advanced celestial survey capability in the northern hemisphere. This effort aims to establish a leading position in time-domain astronomical observations.

A key component of WFST is its large focal plane splicing main camera. The scientific imaging of this camera consists of 9 9K images × Made by splicing 9K CCD chips, the designed imaging target diameter is D325mm. The surface flatness of the assembled image is less than PV20um. This makes it the largest and world leading product of its kind in China. The standard for the flatness of WFST's focal plane inlay is exceptionally strict. The main challenge in developing the main camera is to address high-precision measurement issues, especially in cold conditions. The team solved key technical challenges related to the main focusing camera. This includes vacuum cold packaging of detectors, high-precision measurement and assembly of large target detectors.

The team overcame the challenge of non-contact measurement with high flatness under cold conditions for high-precision measurement of large target detectors. They have developed a differential triangulation method based on laser triangulation, which is suitable for sensors in low-temperature packaging conditions. The measurement error under vacuum sealing shall not exceed 0.5%, and the repeated measurement accuracy can reach ± 2 μ M. On this basis, they completed the development of DTS measurement instruments and ultimately achieved the measurement of WFST main focus camera under low temperature conditions.
At present, the WFST main focus camera has been successfully developed and shipped to Cold Lake, where it will be installed and integrated with the telescope body for calibration and testing.

Source: Laser Network