Objective Infrared target simulator is an important part of infrared target simulation experiment. When the outgoing pupil of the collimation system coincides with the incident pupil of the detection equipment, it can provide a stable infinitely far simulated target for infrared detection equipment, and the simulation results have the advantages of being accurate, controllable and repeatable experiments, which are used to evaluate the performance and accuracy of infrared detection equipment. It has important applications in radar testing, infrared guidance, infrared tracking, etc. With the development of photoelectric detection equipment sensor integration and miniaturization, multi-band sensors have become the standard configuration of most photoelectric detection equipment. Due to the changes in the debugging environment and the use of the environment, it is necessary to adjust it frequently, but most of the target simulators in the laboratory are only equipped with a single-band light source, large size is not convenient to carry. Therefore, it is necessary to establish multi-band and small-sized portable target simulators to meet the needs of different usage environments. For this purpose, an off-axis reflective infrared target simulator system is designed in this paper.
Methods A portable infrared target simulator system is built in this paper. A 110 mm aperture parallel light tube of reflective structure was chosen as the collimation system (Fig.2). The optical-mechanical thermal integration analysis of the system was performed to determine the deformation variation of the primary and secondary mirrors and mechanical structure caused by temperature difference (Fig.8). The self-collimating interferometric detection method was mounted using a Zygo interferometer (Fig.11), and the mounting results were judged by the PV and RMS value results of the face shape measurement of the standard plane mirror (Fig.13).
Results and Discussions The portable infrared target simulation system was mounted using self-collimating interferometry, with PV value of 0.356λ （λ=632.8 nm）and RMS value of 0.047λ (Fig.13), which is better than λ/20, and the results are excellent and meet the usage requirements. The results of Zernike coefficient analysis shows that the system aberrations are mainly out-of-focus, tilt and higher order aberrations of more than 5 levels (Tab.5), and the adjustable target disc is designed to compensate and improve the imaging quality. A portable infrared target simulator system is built in the laboratory to test the optical path and verify the imaging function of the system. The infrared camera and head were placed at a distance of 10 m from the system, and the imaging results are shown (Fig.14). The targets of different shapes can be clearly identified, and the imaging function of the system has completely satisfies the demand of simulating targets at infinity.
Conclusions A portable infrared target simulatot system with working wavelengths of 3-5 μm and 8-14 μm is designed. The system is characterized by simple structure, adjustable wavelength, rich target and clear and stable imaging. The wavefront quality of the system was analyzed using Zemax software, and the PV value of the central field of view was 0.013 2λ and the RMS value was 0.003 8λ in the 4 μm band, and the PV value of the central field of view was 0.004 4λ and the RMS value was 0.001 3λ in the 12 μm band. An optical-mechanical thermal analysis of the collimation system was performed, and at a temperature difference of 30 ℃, the deformation caused by the mechanical structure of the displacement of the optical element is much larger than the deformation of the primary and secondary mirrors themselves, reaching the order of 10 μm, and the imaging results have obvious out-of-focus errors, which can be compensated for the out-of-focus errors introduced by the temperature change by refocusing the target disc with adjustable three-dimensional position. The imaging function of the system was tested, for different shapes of targets, the system can become a clear and identifiable image, providing a stable simulated target for infrared detection equipment.
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