Silicon nitride ceramics have excellent properties of corrosion resistance, wear resistance and resistance to high-low temperature impact, which are commonly used in thermal protection materials of hypersonic vehicles. The laser weapons are the main technical means for intercepting and striking the hypersonic targets in the future. The Nd3+:YAG solid-state pulsed laser was used as an irradiation source and hot-pressed sintered silicon nitride ceramic was used as the target. Meanwhile, the echelle grating spectrometer was used as the detector to construct an experimental system. The radiation spectra of the target with a laser wavelength of 1 064 nm, pulse width of 15 ns, and different energies (50 mJ~500 mJ) were collected. Line identification was based on the national institute of standards and technology (NIST) atomic spectrum database. According to the Boltzmann method, the plasma electron temperatures range from 6 203 K~6 826 K, the plasma electron density range calculated by the Stark broadening method is 8.40×1015 cm-3~1.14×1016 cm-3, and the electronic oscillation frequency is 8.23×1011~9.58×1011 Hz. With the increase of laser energy, the electron temperature demonstrates an overall upward trend, and the change of electron density fluctuates.

Based on the detection and transmission characteristics of different wavelength bands of lasers, by analyzing the echo transmission characteristics of typical micro-cameras, a research scheme for multi-wavelength laser feature detection of micro-camera was proposed. The theories of geometric optics and wave optics were used to analyze the structure of the micro-camera and its reflection spectral characteristics, and the echo light field at a certain detection distance was calculated and simulated. On this basis, a multi-wavelength laser detection system was built. The experimental results show that within a certain depth of field, the micro-camera with infrared cut-off filter has the obvious echo spot diffraction ring characteristics for visible light, high fringe contrast and long detectable distance; in the near-infrared band, the target echo power is low, the back-scattering interference is serious, and the detectable distance is short; the short-wave infrared band is hardly affected by the infrared cut-off filter, and 1 550 nm is in the eye-safe band. The experimental results are consistent with the numerical analyses and theoretical simulation results, which indicate the feasibility of short-wave infrared laser detection of micro-camera.

According to the requirements of multi-target and pseudo-random coded laser semi-active terminal guidance, as well as the fast target ranging and other application environments, a hundred hertz and hundred millijoules all-solid-state nanosecond laser was designed to meet the requirements of integrated, miniaturized and practical prototype. Based on the modular time-sharing pump mode, the heat dissipation pressure of the unit volume laser working material and its pump source was effectively reduced. At the same time, the unstable laser resonator technology was adopted to improve the quality of the outgoing laser beam. Finally, the two resonant lasers were combined into one beam through polarization control to realize the output of a high beam quality hundred hertz and hundred millijoules nanosecond pulse laser. The weight of the integrated prototype is only 15.5 kg. At the operating frequency of 100 Hz, the average output laser energy is 112 mJ, the energy stability is better than 8%, the pulse width is 10.8 ns, and the beam quality reaches 11 mm·mrad. This results can basically meet the requirements of multi-target and pseudo-random coded laser semi-active terminal guidance and fast target ranging for laser source excitation.

The calorimetry is commonly used for high-power laser power measurement, but the traceability is complicated. The high-power laser power measurement method based on principle of light pressure with higher measurement accuracy was introduced, the measurement experiment using a balance with an accuracy of 1/105 was designed, the reflectivity and damage threshold of the mirror based on GaAs semiconductor materials were tested, and the properties of mirrors based on GaAs semiconductor materials were determined. Under ordinary laboratory conditions, the power measurement repeatability and linearity were obtained, and the feasibility of balance with an accuracy of 1/105 for high-power laser measurement was verified. Through the experimental results combined with theoretical calculations, it is concluded that the upper limit of the measurement power of light pressure can reach more than 3×104 W by using the balance with an accuracy of 1/105.

In order to obtain the high-power laser beam, the dichroic mirror was used to combine the two different types of pulse and continuous high energy laser beam of typical wavelengths to achieve the high-power and high-energy laser output. Through the simulation analysis of the thermal effect of dichroic mirrors and the far-field laser parameters of beam combination spot, the simulation results of the thermal effect showed that the root-mean-square value of surface thermal deformation of dichroic mirror was 0.004 λ (λ=632.8 nm) with the single laser beam power of 10 kW and the light spot diameter of 15 mm, which satisfied the design requirements of optical elements surface accuracy less than 0.03 λ. Finally, an experimental system based on dichroic mirror of spectral beam combination was developed. The beam combination test of high-power continuous laser and high-power continuous laser, high-power continuous laser and high-energy pulsed laser were carried out respectively, and the beam combination efficiency was higher than 95%. The experimental results show that the spectral beam combination can be effectively applied to the field of high-energy laser.

Aiming at the problem of periodic arch protrusion in laser-induced breakdown spectroscopy (LIBS) data, an improved baseline correction algorithm was proposed. By adjusting the local penalty coefficients, the algorithm which was based on penalized least square method could not only fit the periodic arch protrusion, but also reduce the effect of spectral lines intensity on fitting baseline. Compared with other baseline correction methods, the root-mean-square error (RMSE) of the proposed algorithm was smaller when fitting the simulation baseline, and the correlation coefficients of the calibration curve based on spectral data obtained by the proposed algorithm reached 0.997 2. The results show that compared with the existing baseline removal method, the proposed algorithm can better retain the effective information of the spectral data when the echelle grating spectrometer collecting the baseline of LIBS.

In the manufacturing technology of additive materials, the characterization of dendrites is crucial for analyzing the mechanical properties of laser cladding layer. However, the labeling of the dendrites is mainly completed manually at present, which is time-consuming and easy to introduce artificial errors, while the deep learning can improve the accuracy of target recognition. Based on the U-net network, the BNC-Unet network which was suitable for the identification and segmentation of dendrites was proposed. The serial attention mechanism and the Batch Normalization layer were effectively deployed in the upsampling and downsampling regions to adjust the weight information of image features. The intersection over union (IoU) was selected as the evaluation index of the segmentation results, and the results of original U-net network and different improved methods under this index were compared. In the test set, the segmentation accuracy index of BNC-Unet network for dendrites is 84.2%, which is 8.97% higher than the results of original U-net network. The index shows that the BNC-Unet network can accurately identify the morphology of dendrites from metallographic diagrams of laser cladding layer, and the accuracy of dendrites identification is significantly improved, which is convenient for evaluating the properties of cladding layer after the laser cladding test.

Based on the basic theory of lightwave diffraction, the regulation method of beam distortion in the diffraction process of the Kepler telescope system was studied by using a Gaussian-distributed laser beam. The aberration function method was constructed by using the intermediate-order Zernike polynomial to simulate the four-leaf distortion in the telescope system, and the Zernike factor was introduced into the optical system to compensate for the distortion effect. The results show that the wavelength and aperture have a significant influence on the distribution of singular light intensity, in which the increase of wavelength will change the shape of the light spot, the aperture will affect the intensity and size of the light spot, and the 11th order Zernike four-leaf deformation factor can offset the distortion phenomenon of the telescope system.

High precision grating diffraction laser warning system is a photoelectric countermeasure equipment to judge and locate the incoming laser function. In order to improve the positioning accuracy, an improved algorithm for calculating and fitting the calculation parameters of the spot center was proposed. Firstly, the laser spot was preprocessed, and the center coordinates of the connected area were obtained by using the improved connected area marking algorithm and spot center extraction algorithm. Secondly, the azimuth angle and pitch angle were set, the images were collected and the spot center was calculated, and the pixel horizontal and vertical coordinates in x and y direction as well as fitting surfaces of laser parameters were fitted, so as to judge the azimuth angle, pitch angle and wavelength of the incoming laser. Finally, the improved connected area marking algorithm, spot center extraction algorithm and parameter fitting calculation results were compared with the traditional algorithm. The experimental results show that the pitch angle error between the fitting calculation results and the real data is less than 0.4°, and the azimuth angle error is less than 0.2°, which greatly improves the accuracy of laser direction recognition.

The pinhole runner is the key component of the optical-path automatic calibration system of an experimental device, and the repeated positioning accuracy is one of its important indexes. In order to effectively measure the repeated positioning accuracy of the pinhole runner in vacuum environment, a measurement method based on the combination of laser and charge coupled device (CCD) was proposed, and the position repeatability of laser spot center of runner filtering pinhole was taken as the evaluation index of its repeated positioning accuracy. A complete set of measurement system was built, the laser spot filtered through the runner filtering pinhole was collected by CCD, and the laser spot image was preprocessed by the image processing methods, such as filtering and noise reduction, threshold segmentation, binarization and edge detection. The least square method was used for circle fitting of the laser spot, and the center coordinates of laser spot were obtained. Compared with laser interferometer in non- vacuum environment, the angular deviation between them was only 11″, which showed that the measurement method had high accuracy and met the measurement requirements. Finally, the repeatability measurement of the pinhole runner in vacuum environment was carried out for about 60 times forward and backward reciprocation in about 6 hours. The results show that the method can effectively measure the repeated positioning accuracy of the pinhole runner in vacuum environment.

The research on oil-gas leak from the central drain pipe of floating-roof tank is of great significance for the timely formulation of reasonable emergency measures and the prevention of major accidents. A method for judging the leak of the central drain pipe was introduced. The influence of different leak locations on the alarm time after the leak of central drain pipe was analyzed through the numerical simulation. The simulation showed that the maximum difference between alarm times of the three leak locations was 1 308 s, which meant that the leak location had a greater impact on the alarm time. The feasibility of laser detection of oil-gas leak in central drain pipe was verified by using CH4 with a concentration of 10% instead of the oil-gas. The results show that the tunable diode laser absorption spectroscopy (TDLAS) technology can be used to detect the oil-gas concentration in the leak alarm system of central drain pipe, which provides a certain reference meaning for the design of the leak alarm system of central drain pipe of floating-roof tank.

In the process of the laser ultrasonic surface defects detection, the quantitative characterization of the defects mainly depends on the operator's judgment, and it is easily interfered by the human factors, which leads to the unstable detection results. To solve this problem, an defects automatic classification detection method based on the two-dimensional convolutional neural network (2D-CNN) for image recognition was proposed. The finite element method was used to simulate the laser ultrasonic detection process, and the ultrasonic signal data was collected for training the classification model; the continuous wavelet transformation (CWT) was used to process the ultrasonic signal to obtain the wavelet time-frequency images, and the images were used as inputs to train the convolutional neural network (CNN) classification model to realize the automatic classification of the surface defects depth. The verification results show that the proposed detection method can accurately classify the defects of different depths, and the average accuracy rate of the test reaches 97.3%; the constructed CNN classification model can independently learn the defects features of the input images and complete the classification, which improves the stability of the test results, and provides a new idea for the automatic analysis and processing of laser ultrasonic defects detection.

The ring laser gyro (RLG) light intensity mode-scanning curve is the basis of the frequency stabilization, and also is the basic characterization of the oscillation characteristics for RLG ring laser and is one of the important signs of the gyro performance. By introducing a new parameter which called mode height, other characteristics of the light intensity mode-scanning curve were described. The mode height of the light intensity mode-scanning curve was the maximum variation of the corresponded light intensity under conditions of one 0.632 8 μm cavity length change, which was a characteristic quantity reflecting the sharpness of the light intensity mode-scanning curve. This characteristic quantity was directly related to the gyro frequency stabilization accuracy and the frequency stabilization response time. The higher the mode height, the higher the corresponding frequency stabilization accuracy, and the shorter the frequency stabilization response time. The physical mechanism of the mode height in RLG scanning process was analyzed theoretically, and the main factors affecting the mode height were determined. Through the theoretical analysis and the numerical simulation, it is concluded that: by increasing the curvature radius of spherical mirror, increasing the cavity length, reducing the loss and increasing the gain, the mode height of the RLG light intensity mode-scanning curve can be increased more than 3 times, which has important guiding significance and practical engineering value for improving the frequency stabilization accuracy, shortening the frequency stabilization response time, reducing the nonlinear error of gyro proportional factor, and improving the fast stability of RLG.