Infrared imaging systems play an important role in many fields. With the increasing demand for system miniaturization, infrared computational imaging technology achieves aberration correction through image restoration algorithms, becoming an effective way to simplify system configuration. The accurate modeling of detector noise is a critical step in infrared computational imaging technology, and its precision directly impacts the efficacy of image restoration. This article elucidates the random noise model of pyroelectric detectors through experimental research and proposes a dynamic noise model to enhance the performance of infrared computational imaging systems. The study initially established a noise testing system for pyroelectric detectors, designed to operate under various temperature conditions in accordance with the specifications of infrared detector noise testing. Subsequently, it conducted a comprehensive analysis of the detectors' noise characteristics. The test results indicate that the random noise conforms to a Gaussian distribution without Poisson components. Furthermore, as integration time and detector temperature increase, the noise demonstrates linear and exponential growth trends respectively. Building upon these findings, dynamic noise models were integrated into imaging noise simulations. Results show that compared with traditional single random noise models, the newly proposed dynamic model improves peak signal-to-noise ratio by 9.17dB, demonstrating its effectiveness in enhancing performance within infrared computing imaging systems. Through extensive exploration into random noises associated with pyroelectric detectors and proposing dynamic models for such noises, this paper not only advances understanding regarding their characteristics but also presents novel strategies for optimizing infrared computational imaging systems—offering significant theoretical significance and practical value.
External cavity spectral beam combining (EC-SBC) is an effective method for improving power while maintaining high beam quality. However, the short focal length design of EC-SBC system often leads to thermal crosstalk, resulting in a failure of wavelength locking. In this paper, the influence of quantum cascade laser (QCL) array spacing and system focal length on the wavelength locking of the EC-SBC system is theoretically analyzed, and it is obtained that a longer focal length can significantly improve the focusing of the QCL beam and the system's wavelength locking ability. By incorporating folding mirrors, the system's length is significantly reduced while maintaining a long focal length, effectively avoiding thermal crosstalk among QCLs. A 3-channel 8.5-μm broadband Fabry-Perot quantum cascade laser (FP-QCL) combined system has been successfully realized, with a beam quality M2 better than 1.8 and a beam combining efficiency exceeding 50%. Additionally, the impact of QCL temperature fluctuations on system wavelength locking is further investigated, and it is found that when temperature is controlled within a range of ±0.5°C, the system can maintain wavelength locking stability. This study provides novel insights for EC-SBC system design, enabling effective expansion in the number of QCL arrays and ensuring beam quality without increasing the total length of the system. It also offers important guidance for enhancing EC-SBC system performance and stability.
Imaging spectrometer with a broad spectrum (such as 400-1700nm) plays an important role in searching for crime scene evidence. The requirement for quickly finding evidence at the crime scene pushes the imaging spectrometer to be more compact. With the development of freeform technology, the Schwarzschild imaging spectrometer with freeform surfaces has good optical performance and compact size. In this paper, aberration correction grating was used in the freeform Schwarzschild imaging spectrometer, which brought more freedom to correct the system aberrations and made the imaging spectrometer more compact. Based on this concept, the compact imaging spectrometer with aberration correction grating is an F/3.2, long slit (12.8mm) with 640 pixels design, covering the spectral range 400-1700nm with 2.6nm sampling. The design results indicate that good optical performance and manufacturability of the system are obtained. Compared with traditional freeform imaging spectrometer, whose optical system volume is 95mmX135mmX52mm, this design volume is only 85mmX125mmX48mm, almost 23% smaller than freeform type, which is very portable for on-site crime scene evidence inspection.
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