This PDF file contains the front matter associated with SPIE Proceedings Volume 12554, including the Title Page, Copyright information, Table of Contents, and Conference Committee listings.

With the development of laser and photoelectric technology, narrowband sodium (Na) Doppler lidars which can measure temperature and wind in the mesosphere and lower thermosphere (MLT) region were established in several observation sites in China. In this paper, the observation of temperature and wind in both nighttime and daytime by a Na lidar recently established in Lanzhou, China (35.95°N, 104.13°E) was reported. The multichannel data acquisition system based on MCS8 was introduced, and the preliminary observational results obtained on January 2022 was presented. The temperature profile measured by lidar was compared with the result from satellite, showing basically consistent trend between 80 and 110 km.

Accurate segmentation of building facade point clouds is the key to 3D reconstruction of buildings. The region growing algorithm is widely used because of its simplicity and ease, but the traditional region growing algorithm leads to over-segmentation and under-segmentation problems due to the low robustness of seed points and the large differences in local features of building facade point clouds. To address the above problems, this paper proposes a building facade division based on FPFH feature classification and regional growth. Firstly, Kd-Tree is constructed to spatially index the facade point clouds and construct geometric topological relationships for the cluttered point clouds. Then, FPFH feature values are calculated and sorted for classification, while the points with relatively low feature values are selected as the initial seed points to ensure the stability of the seed points. Finally, the initial seed points are used as the reference for regional growth and face slice segmentation of the building facade point cloud. The experimental results show that the correct rate of the method in this paper is improved by 14.60%, the over-segmentation rate is reduced by 86.20%andtheunder-segmentation rate is reduced by 43.13% compared with the region growing algorithm, which not only improves the over-segmentation and under-segmentation problems, but also increases the segmentation accuracy as well as efficiency.

Geiger mode Avalanche Photo Diode (Gm-APD) array lidar is a lidar that can perform single-photon detection. It offers a wide range of applications due to its low power consumption, small size, and extended detecting distance. There haven't been many research on this detector's target classification because of its late development and small detector array. The classification technique based on the Gm-APD array lidar point cloud is the focus of this paper's research: Firstly, the Gm- APD array lidar is utilized to perform imaging tests on four targets from various angles in order to create a target classification dataset.Following that, several data preprocessing methods were chosen and implemented based on the characteristics of the obtained data, such as filling in missing values, performing range image and intensity image interpolation, using the principle of keyhole imaging to convert the range image to point cloud data, realizing the information fusion of distance image and intensity image, and using multiple point cloud data enhancement methods. Finally, the point cloud classification networks PointNet and PointNet++ are trained on point cloud data with varying levels of preprocessing, the results are compared and analyzed, and the impact of different preprocessing methods on the classification accuracy of the two networks is determined. Inferences were made and experiments were carried out to verify the inferences. The data set preprocessing method with the highest classification accuracy of the two networks is discovered, laying the groundwork for future Gm-APD lidar target classification and detection research.

To address the problems of insufficient utilization of spatial and spectral information and the need for large number of training samples in the current hyperspectral image classification methods based on deep learning, a algorithm(or model) named 3D Convolution Capsule Network (3D Conv-CapsNet) is investigated in this paper. A 3D convolution-capsule layer is constructed by combining the local connectivity in CNN and the capsule layer in Capsule Network. With the 3D convolution-capsule layer as the core, 3D Conv-CapsNet can acquire and utilize both spatial and spectral information of hyperspectral images, reduce the number of parameters and computational cost of the model, improve the feature representation capability of the capsule, and provide accurate classification results even in the case of limited training samples.In this paper, the classification results of 3D Conv-CapsNet on two hyperspectral image datasets, Salinas (SA) and Pavia University (PU), are analyzed and compared with SVM, 1D-CNN and 2D-CNN and 3D DenseNet. The experimental results show that, with 10% training samples, 3D Conv-CapsNet achieves 99.96%, 99.89% overall classification accuracy on SA and PU, which is better than SVM, 1D-CNN and 2D-CNN and 3D DenseNet. And the overall classification accuracy of 3D Conv-CapsNet network is still over 97% when the training samples are reduced to 5%, 3% and 1%.

Building installation quality inspection is an active research field in the overlapping fields of engineering survey and civil engineering. Furthermore, ensuring the installation quality of temporary buildings in large-scale sports events has more practical and social significance. In this paper, Terrestrial Laser Scanner (TLS) is used to acquire the point cloud of the steel portal frame of the Zhangjiakou Olympic restaurant. Based on the established building coordinate datum, the data of the whole model is simplified, components are extracted and classified. This paper presents an automatic measurement method of verticality and deflection based on point cloud model. The results demonstrate that the mean error of verticality of the steel portal frame is ±0.002 m, and the mean error of member deflection is better than ±0.028 m. The whole structure installation quality meets the specification requirements. The terrestrial laser scanning (TLS) measurement meets temporary building installation detection accuracy requirements.

An iterative slicing reconstruction method for point cloud surface holes is proposed to address the problem that the traditional hole repair method fails in repairing surface holes with uneven density. Firstly, the least squares micro-slices are used to detect and extract the point cloud hole boundaries, and then the least enclosing box is constructed and initially rasterized to achieve a uniform segmentation effect. Then the density of segmentation results is analyzed and judged, and if the density is too large, iterative slicing calculation is performed to obtain uniformly dense segmentation blocks. Finally, the moving least squares method is used to fit each slice data to reconstruct the missing part of the point cloud surface. Our results show that this method can achieve the effect of filling the point cloud holes and averaging the point cloud density as well as improving the accuracy of hole repair for holes containing curved surfaces or point cloud data with uneven density.

To improve the reliability of Rayleigh lidar temperature detection, the feasibility of the Kalman filtering method in Rayleigh lidar temperature retrieval under the condition of an unknown model will be studied. The state model is directly determined by the temperature profile of the NRLMSISE-00 standard atmospheric model, and the corresponding simulated lidar echo data are used as input to compare and analyze the temperature retrieval from the state models of different dimensions to verify the feasibility and reliability of the Kalman filter algorithm.

Road high precision mobile LiDAR measurement point cloud is a digital infrastructure in the fields of high precision map, automatic driving, High-precision automatic semantic segmentation of road point cloud is a key research direction at present. aiming at the problem that the semantic segmentation accuracy of existing deep learning networks is low for the uneven sparse point cloud measured by mobile LiDAR system, a deep learning method is proposed to divide point cloud data according to spatial location and considers the sampling point radius of regional groups. According to the spatial position of different objects, the method extracts the high-dimensional features of sampling points, and achieves the improvement of semantic segmentation accuracy of variable point cloud measured by high-speed mobile LiDAR system and carries out semantic segmentation experiment of The average test accuracy is 97.6%, and the mIOU reaches 0.82. The results show that compared with existing methods, the semantic results show that compared with the existing methods, the semantic segmentation accuracy of the proposed method is significantly improved for the uneven sparse road point cloud of mobile LiDAR system.

The automatic detection of subway tunnel lining disease is realised primarily by using industrial cameras and deep learning. However, due to the uniqueness of subway tunnel environments, industrial cameras can be subject to excess interference and most of the methods are not based on disease characteristics, leaving much room for improvement. This paper proposes a method using point cloud data and a mask region-based convolutional neural network. Using two types of diseases— that is, lining water leakage and dropblocks—as the research objects, the reflection intensity and three-dimensional space information of laser point cloud data were respectively used to generate grayscale and depth maps. Based on the MASK R-CNN learning framework, the proposed method realises the simultaneous detection of two types of diseases, and performs pixel-by-pixel analysis on the feature map through the mask branch to generate a binarised mask. Experiments showed that the disease identification method proposed in this paper could achieve a global accuracy rate of more than 95%, the mAP index value being 0.4. The prediction boxes obtained could cover a more complete disease area. The proposed method combined the advantages of a grayscale map, depth map and mask R-CNN network to achieve simultaneous object detection and instance segmentation for water leakage and drop blocks, and achieved high recognition accuracy and excellent mask results—that is, the area value of the mask could be used as the basis for judging the severity of the disease, providing a certain reference for subsequent maintenance and actual operational application.

A high-power linearly-polarized all-fiber single-frequency amplifier at 1064 nm based on tandem corepumping is demonstrated by adopting large-mode-area (LMA) fiber with core/cladding diameter of 20/130 μm. The output performance of the amplifier dependence on the input signal power has been investigated, and the results indicate that enhancing the injection signal power is advantageous in mitigating the amplified simultaneous emission (ASE) and increasing slope efficiency. A maximum output power of 252 W with corresponding slope efficiency of 85% is achieved with injection signal power of 7 W. At the highest output power status, a polarization extinction ratio (PER) of 17 dB and a beam quality of 1.15 are obtained respectively. In addition, by virtue of LMA fiber and tandem core-pumping, the amplifier exhibits good performance on thermal load, which in turn facilitate the maintenance of frequency noise and linewidth. To the best of our knowledge, this is the highest output power of single-frequency all-fiber amplifier based on core-pumping scheme.

A coherent dual-frequency lidar architecture for long-distance high-precision ranging and velocity measurement is proposed, using the method of optical heterodyne detection, which can avoid complex optical coherence configurations. The system uses a dual-frequency laser with a beat frequency of 200MHz as the dual-frequency light source, and performs measurement through the principles of phase ranging and Doppler velocimetry. The experimental verification shows that the operating distance of the system reaches 3200m, the distance resolution is less than 0.5m, and the speed measurement accuracy range is ±0.25m/s. The results show that the system can realize long-distance high-precision single-point ranging and speed measurement.

Most of the existing mobile LiDAR measurement systems adopt GNSS/INS combination method. This method requires GNSS signal to correct IMU positioning and attitude determination continuously. When GNSS signal is not received, IMU positioning and attitude determination accuracy rapidly increases from centimeter level to sub-meter level or even meter level. In order to solve the positioning defect of mobile measurement system when there is no GNSS signal, In this paper, a dual-mode mobile LiDAR measurement system integrating GNSS/INS positioning and INS/odometer positioning is proposed. It mainly judges whether there is GNSS signal input through the time synchronization controller and automatically switches between the two mode When there is GNSS signal, GNSS/INS positioning is used. When there is no GNSS signal, it automatically switches to INS/odometer positioning mode When there is no GNSS signal, The time synchronization controller simulate GNSS signal, collects its own high-precision quartz crystal oscillator to record time, and converts it into NEMA standard time signal and PPS signal for time synchronization of each sensor. The dual-mode mobile LiDAR measurement system can not only be used in highway measurement, but also solve the pose error in the case of GNSS unlocking such as subway and tunnel. It can be applied to point cloud measurement in a variety of scenes.

In this paper, we have experimentally demonstrated a 4.45 kW master oscillator power amplification (MOPA) narrow-linewidth fiber laser based on fiber Bragg grating (FBG) with near-diffraction limited beam quality. By optimizing the structure of narrow linewidth fiber oscillator seed, the temporal characteristics of injected seed laser is improved. Combined with optimizing pumping ratio of amplifier stage, multiple nonlinear effects are mitigated. Finally, a 4.45 kW narrow linewidth laser output with near-diffraction limited beam quality is achieved with a slope efficiency of 80.2%. The signal to noise ratio is 24.5 dB at the maximum power. The 3 dB and 20 dB bandwidth are 0.5 nm and 3.63 nm, respectively.

A compact dual wavelength Nd:YVO₄/MgO:PPLN infrared laser was developed successfully which was composed of Nd:YVO₄ crystal, MgO:PPLN crystal and a cavity mirror(M1). The fundamental laser was consisted of the first face of Nd:YVO₄ and M1, and the optical parametric oscillation(OPO) cavity defined by the second face of Nd:YVO₄ and M1. The infrared laser output with wavelengths of 1539 nm and 3447 nm was obtained using intracavity cw OPO technology. The output power of 1539nm and 3447nm were 670mW and 236mW at the pumped LD power of 6.0 W, and the optical conversion efficiency was 15.1%. The higher conversion efficiency was mainly attributed the 2mm thickness of MgO:PPLN crystal. Intracavity dual wavelength laser can be used in spectrum detection, drunk driving test and so on.

Middle-wave band infrared imagers and long -wave band infrared imagers have their own advantage and disadvantage under different scenario. Nowadays, the infrared imaging detection system has been developed to the third generation: dual/multi band infrared imager. For a dual/multi band infrared imager, image fusion is a significant research topic. The core of dual band infrared image fusion is to integrate corresponding information from different band infrared imager into a new image. We proposed a new image fusion technology for middle-band infrared image and long-wave infrared image. This technology firstly extracts elementary image semantic, and fuses middle-band infrared image and long-wave infrared image in terms of their elementary image semantic, and then colors the new fusion image in terms of the response characteristics of the scenario in different bands. Finally, the experiment shows the effectiveness of our fusion technology.

The rotational Doppler effect (RDE) occurs when a vortex beam carrying orbital angular momentum (OAM) is normally incident on the center of a rotating target, which is widely applied for the angular velocity measurement of the rotating target and OAM detection. The combined vortex beam based on coherent beam combining technology has many unique advantages, such as high power and excellent quality. In this paper, the combined vortex beam is used as the detection source to measure the rotating target at a distance of 1 kilometer, we prove the feasibility of the combined vortex beam can be used to measure the rotational speed. However, there are some misaligned incidence conditions such as lateral displacement and oblique angle between the optical axis and the rotation axis. We analyze the change of the OAM spectrum and characteristic peak’s intensity with the increase of misalignment. The results show the OAM mode of the probing beam will expand to the adjacent modes, resulting in a series of discrete frequency-shifted signals including the characteristic peaks, when the optical axis does not coincide with the rotation axis. When deviation exceeds a certain value, the dispersion is too large to cause the frequency characteristic peaks are gradually submerged in the scattering signals. These analyses provide a reference for the practical detection of rotational speed in remote sensing.

Inhalable particulate matter has been widely concerned due to its serious harm to human health in China. Real time, rapid and high-resolution monitoring of particle concentration change is the first step to prevent and control inhalable particle pollution. In this paper we present a method for detecting fine particle mass concentration based on forward and lateral light scattering measurement. Based on Mie light scattering theory, we design and establish the experimental platform of multi-angle light scattering measurement. Moreover, a portable multi-angle light scattering detection particle mass concentration prototype is developed by using computer modeling, 3D printing and weak photoelectric signal detection technology. Through theoretical numerical simulation and experimental analysis of optical platform, 20° forward and 45° lateral are selected as the optimal detection angles with the advantages of simple structure and high efficiency. Finally, we obtain the pulse reference voltage of different particle size segments is to realize the particle size segment detection. A specific case of our nonlinear regression algorithm is used to calibrate parameters of the detection system. The feasibility of the proposed detection method is verified by the comparative detection experiments in the laboratory and the outdoor atmospheric environment.

Lidar is an important device for detecting atmospheric parameters. In this paper, a single channel F-P etalon is used as a narrow-band filter to lock the transmittance of 355 nm wavelength emitted laser by control the transmittance of seed laser with 1064 nm wavelength. Not only the background noise can be suppressed and the signal-to-noise ratio can be improved, but also the transmittance of the locked target in the etalon can be tracked to achieve higher detection accuracy. During the experiment, transmittance is controlled at target transmittance with 0.01 precision.

In the process of optical remote sensing image imaging, shadow areas often appear in remote sensing images due to the occlusion of sunlight by vegetation, buildings, clouds and other objects. These shadow areas often contain a lot of important information and targets, which have a great impact on ground target recognition, feature edge extraction, and surface information inversion. Especially as the resolution of remote sensing images has entered the sub-meter level in recent years, the need for efficient shadow compensation methods has become more and more urgent. In this paper, aiming at the problem of color distortion after the common shadow compensation algorithms, combining with the typical characteristic of half-shadow area and the concept of Homogeneous area, this paper improve the formula of Wallis filter and research an improved shadow compensation algorithm based on Lab color space. Wipe off the boundary of shadow areas, keep the visual coherence of the image better. The experimental result shows that the algorithm can achieve a better performance without manual intervention.

Increasing numbers of people have taken up skiing in recent years due to the strong promotion of the Beijing Winter Olympics in 2022 by We Media. Nowadays, the establishment of three-dimensional digital twin snow fields has become an important way to effectively manage and maintain snow fields. However, due to the large altitude difference and the presence of many trees and rocks in ski resorts, traditional methods face difficulties such as low segmentation accuracy and low merging efficiency of segmentation blocks when performing semantic segmentation of ski runs. Consequently, this paper proposes a contour extraction method of artificial ski runs using composite supervoxels based on the characteristics of artificial ski resorts. To begin with, the point cloud data set of ski resort is segmented to get supervoxels; secondly, the difference in elevation between the seed supervoxel and the adjacent connecting block is calculated to determine whether the merging plane is the ground or another plane; then, according to the normal vector angle threshold and the orthogonal distance threshold, the similarity between the current clustering region and adjacent blocks is evaluated; and finally, the region growth algorithm is optimized based on the point cloud supervoxels of ski resorts, in order to reap the benefits of ski track semantic segmentation. And experiments have shown that the proposed method is superior to the other two in terms of segmentation accuracy, efficiency, and robustness, and is suitable for the segmentation and extraction of ski tracks in complex scenes, such as artificial snow fields.

In the application of cavity ring-down (CRD) high reflectivity measurement, precise adjustment of ring-down cavity (RDC) is of great importance. The transmission spot shape monitoring, which contains the judgment of the mode order and nodal direction of intracavity transverse mode, is an important method for cavity adjustment. In this paper, several criterions of circumscribed spot shape are compared. After spot binarization, the circumscribed circle, circumscribed rectangle, and circumscribed ellipse of transmission spot is analyzed, respectively. The theoretical comparison shows that the circumscribed ellipse criterion can effectively distinguish the mode order and nodal direction simultaneously. The spot can be recognized as the fundamental transverse mode when the area ratio of the spot to its circumscribed ellipse is in the range of 0.9 to 1.0. This method is tested by an experimental setup. It is found to be an efficient cavity adjustment method for the CRD technique.

There is abundant information in molten pool and keyhole during laser deep penetration welding. Their stability and characteristics are closely related to welding quality. At present, visual monitoring is an important means to obtain the characteristics of molten pool and keyhole. However, how to obtain a clear image, and how to optimize or develop an accurate and efficient algorithm are two major problems facing the visual monitoring of molten pool and keyhole. In view of the above problems, the paper combs the factors affecting molten pool visual monitoring and molten pool recognition algorithm. Firstly, the effects of camera type, auxiliary light source and filter, image acquisition method, the shielding gas and the air pressure on the image clarity of molten pool and keyhole are emphatically analyzed, and a method conducive to visual monitoring of molten pool and keyhole is proposed. Secondly, the influence of different algorithms and models on the monitoring accuracy of the system is analyzed. It is found that image pre-processing can highlight molten pool image information, and DBN (Deep Belief Networks) model has higher prediction accuracy through the processed molten pool image. Pointed out in the end of this article, the development of a laser welding monitoring device with clear image, stable and high dynamic response, the integrated development of multi-sensor synchronization visual monitoring device, and the development of laser welding process of adaptive fusion image processing algorithms will be the focus in the future, which provides a research direction for monitoring of molten pool and keyhole.

A high power laser measuring device based on radiation pressure is built. The mass measurement repeatability and the laser power measurement repeatability were experimentally studied. The experimental results show that the measurement repeatability of the radiation pressure measuring device gradually decreased with the increase of the measured mass and the measured laser power, indicating that the radiation pressure method has more advantages in measuring high power lasers. In the laser power measurement repeatability experiment, the influence of eccentric load and airflow disturbance is avoided, so the laser power measurement repeatability is better than the measurement repeatability calculated according to the equivalent mass.

For the accurate fitting of cavity decay rate in cavity ring-down technique, the theoretical fitting bias of the weighted least square algorithm for decay signal modulated by definite systemic response time is analyzed and tested. After proper data-point truncation, the finely precise and highly accurate fitting of cavity decay rate can be achieved simultaneously. This method is tested by experimental decay signals, results in better fitting performance than the nonlinear least square fitting (the Levenberg-Marquardt) algorithm.

With the development of laser technology, nanosecond lasers have been widely used in material micromachining due to their advantages such as the narrow pulse width and high-power density. The high-order harmonic generation procedures have been invented to obtain 532, 355, and 266 nm radiations based on a 1064 nm Nd:YAG laser. In this paper, the influence of different sample moving speeds and laser power on the cutting effects were studied using three kinds of laser sources. It can be seen that the state of the cutting surface has not changed obviously when the laser power was increased. The self-defined cutting threshold, i.e., 2.25 W·s/mm, has been obtained by investigating the processing morphology with the power of 1.35 W at different sample moving speeds for both a 355 nm laser and a 266 nm laser. Increasing the laser power to 3.20 W, we obtained the cutting threshold of about 1.80 W·s/mm for a 355 nm laser. The scorching status of the surfaces cut by both a FHG laser and a SHG laser have been found to be more serious than that cut by a THG laser. The experiments have demonstrated that the machining efficiency increases with the laser power, but the cutting quality becomes worse at the same time. The results are thought to be useful for the PCB cutting applications in the industrial fields.

Tunable diode laser absorption spectroscopy (TDLAS) technique has been widely investigated for gas concentration measurement in both industry and laboratory. In order to detect different gases within the multi-gas mixture based on TDLAS, different types of schemes have been developed, such as wavelength division multiplexing, time division multiplexing and so on. However, there are many drawbacks of the above methods, such as the slope of normalized baseline restricted the sensitivity and accuracy, the effect of cross-talking interferences becomes a technical bottleneck for multi-gas detection. Therefore, a high sensitive synchronous detection technology for multi-gas detection using the multiple linear regression analysis method is reported. The wavenumber of 4291cm^-1 has been selected to detect CO and CH₄. Several characteristic points are selected to establish multiple linear regression equations, then the concentrations of CH₄ and CO can be calculated, and the baseline can also be obtained simultaneously. The Allan variance results indicate that the optimal integration time has been improved to ~60s, the minimum measurement precision of CH₄ and CO is ~0.58% and ~0.41×10^-6 respectively. Meanwhile, the detection cost and response time can be reduced obviously

Laser Doppler velocimetry system is very important in the production and application of high temperature target velocity measurement without contact. In order to quickly and accurately select the wavelength of laser velocimetry system in high temperature environment and effectively improve the signal-to-noise ratio. In this paper, a new scattering model and thermal radiation power calculation method are presented to simulate the signal power and thermal radiation power in the process of velocity measurement. The accuracy of the model is verified by experiments, and the error is within 3%. In addition, according to the SNR formula, the system parameters can be adjusted to make the velocity measurement system with 1550 nm wavelength also feasible under the background of strong infrared radiation, which has important guiding significance for the design of the velocity measurement system for high temperature targets.

Biomimetic mushroom-shaped microstructures could ignite applications as dry adhesives and super-hydrophobic surfaces, however its facile fabrication still remains a challenge. In this work, we have proposed and demonstrated the facile fabrication of high-density mushroom-shaped microstructures using the photo-lithographic technique. The inverse “T” shaped light exposure in the photoresist directs the formation of the relief microstructure during chemical development, which serves as the mold for the bio-inspired surface. The requirement of one positive photoresist and one-step chemical development greatly simplifies the fabrication process, which also improves the reliability of the approach. The mushroom-shaped microstructures show significant super-hydrophobic properties and has high contact angles (157.2°). The liquid-repellent properties would be tailored by varying the densities of the mushroom-shaped microstructures, which was further exploited for droplet transportation and fusion. The effects of fabrication conditions on the parameters of the mushroom-shaped microstructures were also investigated. This new approach enables facile and controllable fabrication of mushroom-shaped microstructures, implying the potential for practical applications.

In this paper, a series of experiments of drilling holes and slotting micro-channels on the 1 mm-thick BK7 or 1.1 mmthick B270 glass substrates are introduced by employing three types of Q-switched lasers with the wavelength of 1064, 355, and 266 nm. Firstly, by smearing the solution of NiSO4∙6H2O on the front surface of BK7 glass plates, we successfully realized drilling holes on the glass substrates by employing a 1064 nm fundamental Nd:YAG laser. Then, we also carried out the experiments of drilling holes by utilizing a normal third-harmonic-generation (THG) 355 nm Nd:YAG laser and a 266 nm FHG (forth-harmonic-generation) laser. It can be found that the diameters of drilled holes by utilizing a 355 nm laser are larger than those by utilizing a 266 nm laser, and the holes with both two wavelengths lasers did not change a lot when the exposure time of lasers was increased from 0.5 s to 30 s. Finally, the experiments of slotting micro-channels on B270 glass plates were undertaken by utilizing both a 355 nm laser and a 266 nm laser. It has been found that the cracks around slotted micro-channels become lesser when the moving speeds are increased for both experiments. The channel widths of using the 355 nm laser are around 10 times smaller than those of using the 266 nm laser. As a conclusion, among three kinds of lasers, the 355 nm laser may be the most suitable type for the glass micro-processing with high precision in practice.

For the urgent demand of the broadband, high efficient, parallel processing and high speed frequency hopping capability in the field of ultra-wideband measurement control and communication, this paper puts forward a kind of channelized receive technology based on microwave photonic technology. The coherent optical comb generation module generates the signal optical comb and the local oscillator optical comb, and coherent optical comb with high repetition frequency is obtained by using cascade modulator and nonlinear technique. In order to satisfy the 10 comb teeth designed for the system, the FSR of coherent optical frequency comb is greater than 100GHz and 99.4GHz respectively, and the channel bandwidth is 600MHz. The channel division module receives the frequency hopping signal from the RF front-end and modulates it to the optical frequency comb. By DPMZM single sideband modulation, 10 optical combs can be used to shift the frequency of the oscillator frequency comb. At the same time, according to the position of the frequency hopping signal, the frequency comb is carefully controlled. After the WDM multiplexing device, it is selected by the high-speed optical switch controlled by the control unit. And photoelectric detection and mirror frequency suppression are realized by coherent demodulation, which consists of an optical mixer, a balance detector and a bridge. Which realizes channelized reception and cross-frequency conversion of any 6GHz wideband signal from the DC to 40 GHz band. Achieve 3dB channel consistency and mirror frequency suppression above 30dB. The results are verified by simulation and experiment. This method can be used to receive ultra-wideband ultra-high speed frequency hopping signals.

In long-distance fiber-optic sensing and communication systems, phase modulation methods are usually employed to suppress stimulated Brillouin scattering (SBS), thereby increasing the stimulated Brillouin threshold. However, when phase modulation is added to the light source, the linewidth is broadened by the periodic modulation and the coherence length is reduced. In a large-scale multiplexed fiber optic hydrophone system, the optical pulse interference visibility returned by the fiber optic hydrophone is affected by the optical path difference, phase modulation amplitude and frequency, etc., resulting in reduced visibility of interference fringes. In practical applications, it is difficult to fully compensate the optical path difference between the hydrophone and the time-delay interferometer. In the case of large optical path difference, the phase modulation amplitude and frequency need to be optimized to improve the visibility of the interference pulse. In order to solve this problem, this paper first theoretically analyzes the principle of SBS suppression by light source phase modulation. The laboratory builds a fiber optic hydrophone remote transmission test system, and uses a spectrum analyzer to measure the backscattering spectrum of the transmission fiber to obtain the suppression of SBS. The best parameters for the suppression of the effect, the interference visibility of the hydrophone is tested on this basis, the phase noise of the hydrophone with poor visibility is tested, and the phase noise consistency of the tested hydrophone at 1kHz. By optimizing the modulation parameters of the phase modulator and changing the modulation frequency by using the method of equal step size, the interference visibility of the interference pulse is improved. Improve the visibility of the hydrophone with poor visibility from 0.42 to 0.89, the phase noise of the hydrophone is reduced, effectively balancing the Brillouin threshold and interference visibility, and greatly improving the noise of the hydrophone The consistency is of great significance to the engineering application of the optical fiber hydrophone remote transmission system.

In the photoacoustic microscopy coupled with the optical fiber, the photoacoustic intensity of the irradiated tissue is one of most important factors of Furthermore, the coupling coefficient of the fiber also impacts the final irradiated laser energy. Furthermore, the coupling coefficient of the fiber also impacts the final irradiated laser energy. At the characteristic wavelength of 532nm, the effects of the optical positions of the With the operations of parameters scanning, the optimal values of the optical positions of the focusing lens and optical fiber on the coupling efficiency of the fiber were investigated. values of the optical positions of the focusing lens and optical fiber were obtained under the maximum coupling efficiency of the fiber. After that, the effect of the fiber's mode field diameter on the coupling efficiency of fiber under the optimal positions of the focusing lens and fiber was also investigated. The coupling efficiencies of fiber corresponding to seven different mode field diameters of fiber from 1 to 9μm were computed, the The study results show that with the increase of the mode field Under the optimal positions of the focusing lens and the fiber, as well as the mode field diameter, the optical efficiency of fiber first increase then decrease. Under the optimal positions of the focusing lens and the fiber, as well as the mode field diameter, the optical efficiency of fiber can be improved from 23.174% to 91.638%. Therefore, the reasonable positions of the optical path and the mode field diameter of the fiber are all important to ensure the satisfactory optical Therefore, the reasonable positions of the optical path and the mode field diameter of the fiber are all important to ensure the satisfactory optical coupling efficiency in the photoacoustic microscopy system coupled with the optical fiber.

When laser propagates in the atmosphere, due to the influence of atmospheric turbulence, it will produce spot drift, light intensity flicker, beam spread and other phenomena, which restrict the development of laser engineering. Acoustic wave is a mechanical wave, when it propagates in the atmosphere, it will change the atmospheric density, affect the internal structure of atmospheric turbulence, and then affect the transmission of laser in atmospheric turbulence. In this paper, a coherent acoustic wave generator is designed, and the laser transmission experiment in the outdoor atmospheric turbulence environment disturbed by coherent acoustic waves is carried out. The variations of the beam drift fluctuation variance, scintillation index and beam diameter with coherent acoustic wave frequency and acoustic pressure level are studied. The results show that coherent acoustic waves will change the original structure of atmospheric turbulence and affect the variance of beam drift fluctuation, scintillation index and beam diameter when laser transmitted in atmospheric turbulence; The variance of beam drift fluctuation, scintillation index and beam diameter change with the change of sound source frequency and acoustic pressure level. This paper preliminarily explores the influence of acoustic wave disturbing atmospheric turbulence on laser transmission characteristics, and the research results provide a new idea for improving or interfering laser transmission characteristics in atmospheric turbulence.

Aiming at the issue of rapid establishment of wireless optical communication (WOC) link between two cooperativeterminals, a fast laser beam alignment technique based on laser scanning and echo enhancement has been proposedandrealized. The scanning modes such as rectangular scanning, Lissajous scanning, spiral scanning and rectangular spiral scanning, are analyzed and selected for the system carefully. The cube-corner retroreflector (CCR) are equippedonthecooperative terminal to enhance the echo. The target capturing experiments have been demonstrated in different statesbased on the scheme, and the effect of the CCR’s installing angle on the aligning performance was researchedbyexperiments. The experimental results indicate that the system could capture the CCR at the largest distance of 45meterswithin 22 seconds and track the CCR in the tilting angle ranges of ±30°. The proposed system can automaticallyrealizethe beam alignment effectively and rapidly with the aid of CCR, and the whole alignment process does not need anyhelpof radio frequency (RF) communication signal. The beam alignment scheme is simple and easy to be implemented, andit has the potential to boost the practical application of WOC.

In the field of conventional weapon test and identification, optical measurement is often used to measure the exterior ballistic parameters of targets. With the variety of measuring equipment and measuring bands such as visible light/medium-wave/long-wave, the profile/shape and radiation/luminance distribution of the exhaust plume target imaging in the optical measurement system are great different, so that the target interpretation position changes greatly with the change of the exhaust plume .The variation of the plume depends on the flight state of the weapon system, inmost cases there is no prior data support, we judge by the experience of the surveyors, so this processing mode affects the credibility of the measurement data, especially in the case of high precision requirements such as characteristic parameter and miss distance processing. Aiming at the Consistency problem of multispectral imaging data of the exhaust plume target, using the inversion imaging method of fluid numerical simulation to characterize the multispectral imaging of the weapon system under various flight states, and theoretically evaluate the imaging deviation. Whether this method is feasible depends on accuracy of the wake simulation calculation meets the actual needs. For this reason, the wake combustion products and their components of a certain type of rocket are studied. Based on the plume component analysis, establish a plume directional radiation calculation model. Through the close acquisition of the visible light/ medium-wave/long-wave images in the initial stage of the rocket, the profile characteristic parameters are compared with the simulated radiation images obtained by numerical simulation. The results show that ,the main body of the exhaust plume edge error is located within ± 20%, and the comparison result in the core area of the exhaust plume is better than ±10%,so the profile data of the core area can be used as the reference for consistency analysis. This method breaks through the current situation of systematic error estimation based on experience in theory, and has high guiding significance for the evaluation of the processing accuracy of external ballistic test data.

Coherent beam combination of fiber lasers is considered to be a promising technology to obtain high-brightness laser. In tiled-aperture coherent beam combination, in order to obtain the best combination effect, a high fill factor is required for the beam array output from the fiber collimators. Thus, the collimator array must be closely arranged and each single-mode Gaussian beam must be truncated, which brings great difficulties to design a fiber collimator. We propose a scheme of fiber collimator based on rod lens, which compares to the fiber collimator with the thin lens, has the following advantages. Firstly, rod lenses for beam collimation can be arranged in an array without a frame to get a high fill factor of fiber collimators. Secondly, the single-mode Gaussian beam from fiber can be truncated in any proportion to get a good result of coherent beam combination. Thirdly, almost all of the laser energy output from a fiber include the stray light with the large NA is emitted into space outside the collimator by the rod lens. Fourth, the structure of fiber collimator with the rod lens is simple, which makes it easy to build a large number of fiber lasers array. In this paper, we have developed a rod lens collimator and carried out the preliminary experiments, the results show that the rod lens collimator can emit a collimated beam with the good beam quality, and all stray light with the large NA in the collimator can be exported to space.

Optical phased array is a method of beam control by controlling the wavefront distribution of the beam. It has the characteristics of all-solid state, low power consumption and no inertia. The realization of multi-beam control in free-space optical communication through optical phased array has obvious advantages in energy consumption and control accuracy. The optical phased array modulates the phase directly on the beam ideally, but in fact the optical phased array device parameters obviously have an effect on the complex amplitude of the beam. In this paper, the modeling of the optical phased array device is realized, and the influence of the duty cycle of the optical phased array element on the efficiency and efficiency of the multi-beam control is analyzed. The experimental results show that the optical phase control controls the energy of the multi-beam pointing. The efficiency gradually increased from 0.23 to 0.88 when the fill factor increased from 50% to 100%, and the control accuracy of the optical phase control to control the multi-beam pointing did not significantly correlate with the fill factor. The experimental results have a certain reference for the application of optical phased array in multi-beam control.

This paper introduces a laser amplifier with a non-uniform concentration of ceramic material as a laser gain medium. This gain medium structure prepared by ceramics is a circular thin-disk with a thickness of about 1mm and the size of the cross-section radius(r) is determined by the signal light to be amplified, the pump light absorption efficiency is generally above 96% and the uniformity of the pump light absorption distribution is a predetermined value, such as 96% or higher. The ceramic gain medium of this non-uniformly doped structure adopts a new way to achieve the uniformity of the gain distribution, this way resolves the contradiction between high absorption efficiency and high uniform gain, it is beneficial to realize high-power, high-efficiency and high-beam quality laser output.

Planar laser-induced fluorescence (PLIF) has been widely used in the two-dimensional (2D) accurate measurements of important combustion parameters due to its high spatiotemporal resolution. One of the problems encountered by PLIF technology is that the current beam shaping technology cannot get a sheet beam that meets the measurement requirements. In order to solve this problem, a new sheet-forming homogenization optical system with long focal-depth is proposed and designed based on total reflection integral cavity. By making the incident Gaussian beam reflected multiple times in the integral cavity, the output beam of single direction homogenization can be obtained. The beam is then passed through a beam expansion collimation system and compressed in the other direction. Finally, the shaping sheet-beam with high uniformity is realized. Based on this principle, the ZEMAX is used to simulate the optical system operating at 283.553nm, and it is found that the effect of the final beam shaping is mainly affected by the entry pupil deviation of the incident laser, the integral cavity length and the angle between two reflecting surfaces of an integrating cavity. After optimizing design parameters, a sheet-beam energy homogenization optical system based on total reflection integral cavity is designed. Finally, the homogeneity evaluation factor is introduced to calculate the homogeneity of output beam quantitatively and it is found that the uniformity of the beam is more than 90%. The sheet-beam can better meet the practical requirements of PLIF measurement.

The Stokes-Mueller polarimetry is a well-established measurement technique to provide both purely polarized and partially polarized optical signals. However, this polarimetry is not applicable for the nonlinear optical process second harmonic generation (SHG). To solve the problem involved, a generalized double Stokes-Mueller polarimetry (DSMP) formalism is employed to describe the polarized SHG signals. Instead of a 4×1 matrix for Stokes vector, the double Stokes vector is a 9×1 matrix representing the polarization of two incoming photons, which results in the double Mueller containing 36 elements rather than 16 elements for Mueller matrix. In this paper, we present a specific novel mathematical framework of the light propagation for DSMP. In this paper, all the light propagation process, including the linear optical process and the nonlinear optical process SHG in the sample. Firstly, we introduce the expressions for the Stokes vector of the incoming, outgoing radiations and the Mueller matrix of the linear optical elements. Secondly, the double Stokes vector and the double Mueller matrix similar to the linear Stoke-Mueller formalism is present. Thirdly, to combine a train of linear optical elements in front of SHG and the nonlinear optical process, we design a transition matrix T connecting the Stokes vector and the double Stokes vector. Finally, we get the mathematical framework of the light propagation for DSMP, which has the potential to be part of the error analysis of a polarization-resolved Second-harmonic Generation (PSHG) microscopy.