A frequency stabilizing system for a pulsed injection seeded 1550nm optical parametric oscillator (OPO) at 20 Hz repetition rate is demonstrated. The optical heterodyne method is used to measure the frequency difference between the seed laser and the OPO output. Using the frequency difference as the error signal, a proportionalintegral controller in combination with a scanner is applied to stably match the OPO cavity length to the seed laser frequency. The root-mean-square (rms) error of the frequency discrimination method is <0.07MHz according to a ‘frequency shifting-chopping-beat’ evaluation. The frequency fluctuation of the frequency-stabilized OPO is 0.29MHz (rms), and the Allan deviation is less than 20 kHz for averaging time of more than 3 s.

Artificial intelligence (AI), especially deep learning, is gaining extensive attention for its excellent performance in medical image analysis. It can automatically make a quantitative assessment of complex medical images and help doctors to make more accurate diagnoses. In recent years, AI based on ultrasound has been shown to be very helpful in diffuse liver diseases and focal liver lesions, such as analyzing the severity of nonalcoholic fatty liver and the stage of liver fibrosis, identifying benign and malignant liver lesions, predicting the microvascular invasion of hepatocellular carcinoma, curative transarterial chemoembolization effect, and prognoses after thermal ablation. Moreover, AI based on endoscopic ultrasonography has been applied in some gastrointestinal diseases, such as distinguishing gastric mesenchymal tumors, detection of pancreatic cancer and intraductal papillary mucinous neoplasms, and predicting the preoperative tumor deposits in rectal cancer. This review focused on the basic technical knowledge about AI and the clinical application of AI in ultrasound of liver and gastroenterology diseases. Lastly, we discuss the challenges and future perspectives of AI.

Scanning lidar imaging system using a linear detector array is constituted by both sides into 45° angle of mutual mirror composition. The construction of equivalent optical systems is greatly simplified in the imaging derivation process with intuitive method and analytic geometry. The optical imaging formulas are accurately derived for all the spots of the image. Based on the imaging requirements of the Lunar and Mars exploration technology, numerical simulations and error analysis were performed in the paper. It is shown that the maximum distortion ratio of the central spots pillow-shape distortion image is 3.41% in horizontal direction and the excursion of the edge spots by laser pulse at certain divergence angle is 0.194m, 0.096m in horizontal direction and vertical direction, respectively. The work of this paper can provide the theory basis of the lidar imaging signal processing on-line or off-line used in the deep space exploration projects.

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