Efficient photon-counting imaging in low signal photon level is challenging, especially when noise is intensive. In this paper, we report a first signal photon unit (FSPU) method to rapidly reconstruct depth image from sparse signal photon counts with strong noise robustness. The method consists of acquisition strategy and reconstruction strategy. Different statistic properties of signal and noise are exploited to quickly distinguish signal unit during acquisition. Three steps, including maximum likelihood estimation (MLE), anomaly censorship and total variation (TV) regularization, are implemented to recover high quality images. Simulations demonstrate that the method performs much better than traditional photon-counting methods such as peak and cross-correlation methods, and it also has better performance than the state-of-the-art unmixing method. In addition, it could reconstruct much clearer images than the first photon imaging (FPI) method when noise is severe. An experiment with our photon-counting LIDAR system was conducted, which indicates that our method has advantages in sparse photon-counting imaging application, especially when signal to noise ratio (SNR) is low. Without the knowledge of noise distribution, our method reconstructed the clearest depth image which has the least mean square error (MSE) as 0.011, even when SNR is as low as −10.85 dB.

The wide field of view (FOV) of traditional star sensor optical systems restricts the ability to suppress atmospheric background. An optical imaging system for an all-time star sensor based on FOV gated technology is proposed. In this system, a wide FOV telescope is used to observe a large sky area containing multiple stars. A microlens and microshutter array is employed to subdivide the wide FOV and gate a narrow FOV to suppress atmospheric background radiation. Assisted by a common imaging lens, each set of microlens and microshutter elements corresponds to a FOV gated imaging channel. With the rapid switching of gated FOV, multiple stellar images are obtained on a common detection during daytime. As an example, a FOV gated optical imaging system with 0.4° gated FOV and 61 imaging channels is designed. In addition, a simplified prototype is developed, and a preliminary experiment of FOV gated imaging is performed near the ground. The results verify the capability of multiple stellar detections during daytime. The proposed optical imaging system has a strong capability of suppressing atmospheric background radiation and provides sufficient FOV gated imaging channels to enhance the probability of detecting multiple stars. It provides an effective technical way to develop all-time star sensors based on star pattern recognition and enables a completely autonomous attitude determination possible for platforms inside the atmosphere during daytime.

Photon-counting LIDAR has effective ability to detect significantly weak echo. However, for imaging application, it typically needs a long acquisition time to obtain sufficient counts to reconstruct clear depth image, which obviously limits imaging efficiency and prevents its wide deployment. In this paper, we proposed a low acquisition time photon-counting imaging method based on two single element SPADs and pixel scanning structure. Compared to fast imaging with SPAD array, the method has low requirement on laser energy and can obtain depth image with arbitrary pixel resolution. Experiment result demonstrates its feasibility and a dynamic target can be clearly captured by the system with our specifically designed reconstruction algorithm. We also detailly investigated the working conditions for the method. It reveals more than 2 echo photons per pulse would be enough to reconstruct clear depth image even when noise is intensive. Restricted to our 10 KHz laser source, the result only exhibited 1 frame per second(fps) imaging with pixel resolution of 100*100. If a common 10 MHz laser is adopted, 512*512 pixels resolution images can be captured at the rate of nearly 40 fps.

阐述了多普勒非对称空间外差光谱仪用于被动式多普勒测速的基本原理，通过综合考虑干涉条纹对比度和仪器测速灵敏度等关键因素，建立了效率函数，分别针对高斯线型和洛伦兹线型发射谱线，从理论上推导了最优单臂偏置量的选择依据，并以高斯线型目标谱线为例进行了仿真验证.同时，提出了一种基于部分干涉条纹反演多普勒速度的数据处理方法，简化了多谱线目标源的数据处理过程.结合自适应频率跟踪算法对单谱线目标源和多谱线目标源进行了仿真比较，仿真结果表明，在不考虑噪声的情况下，该方法针对多谱线目标源的多普勒测速最大绝对误差在0.004 m/s以内，与针对单谱线目标源的处理精度相当，可以满足实际应用的精度要求.

In this paper, a weak measurement scheme with double pointers (mean value shift and intensity shift of the post-selected light) is presented to simultaneously measure the tiny polarization change (phase and amplitude) of light in a single experimental apparatus. Furthermore, rather than using charge-coupled-device (CCD) to measure the pointer shift, we use the two-channel photoreceiver combined with lock-in amplifier (LIA) to measure the intensities of a split-Gaussian mode in this work. In this way, we introduce two intensity contrast ratios (ICRs) as special pointers to characterize the mean value and intensity shifts. As a result, the measurement precision of the polarization rotation is on the order of magnitude of $~10^{-7}rad$ in the experiment. These findings provide a distinctive insight into the weak measurement and have important implications for the accurate measurement of complex optical parameters.

The intense atmospheric background in near-earth space has huge interference on the star detection for all-time star sensors. To observe and track stars, traditional all-time star sensors with narrow field of view (FOV) must be installed on turntable platforms, which cannot achieve autonomous celestial attitude measurement. The innovative all-time star sensor based on FOV-gated technology controls the micro-shutter and micro-lens array, enabling rapid switching to subdivide the wide FOV and gate a narrow FOV. This system ensures the detection of multiple stars simultaneously by suppressing atmospheric background radiation, thereby achieving autonomous attitude determination. For the all-time star sensor, the accuracy of attitude measurement is not only related to system parameters but also to atmospheric radiation and transmission. Current parameter optimization methods are constrained by specific observation conditions, limiting their applicability across diverse scenarios and temporal variations. To overcome these limitations, we developed an analytical model that accounts for the distribution of spatiotemporal observation conditions, including the probability distribution of the solar zenith angle. Based on this model, the attitude accuracy of the star sensor under all spatiotemporal conditions is weighted and employed as the global optimization objective. An optimal design scheme was provided through optimization, leading to the fabrication of an actual optical lens, which was subsequently used to assemble a prototype. A ground-based experiment was conducted to validate the accuracy of the star detection model, followed by a simulation that confirmed the proposed design satisfies the requirements in the entire celestial sphere.