2022 Vol. 43, No. 4
The ship-borne electro-optical tracking and fire control system is a kind of long-range monitoring, tracking and fire attack device, which can be divided into discrete system and integrated system according to the architecture. The structural forms, sensor configuration, range and relationship with fire control system of typical electro-optical directors such as MSP500 in Germany, Medusa MK4 in Italy, 2500 in England, Toplite in Israel, SeaFLIR 280-HD and 380-HD in America, EOS500 in Sweden, EMOS NG and PASEO in France were compared and analyzed. The structure of electro-optical directors was gradually developed from T-type to U-type, the band of electro-optical sensor was developed from single band to multiple band, and the function of electro-optical tracking system was changed from single function to comprehensive multi-function. With the intensification of modern naval warfare, the ship-borne electro-optical tracking and fire control system will develop towards multi-sensor cooperation detection, information fusion, multi-target identification, intelligent tracking and mission diversification.
With the development of optical theory and the progress of science and technology, the optical technology has developed rapidly, which puts forward new requirements and challenges to the optical metrology technology. Aiming at the importance of optical metrology in national defense and military, the new requirements of the development of national equipment support for national defense optical metrology were analyzed, and introduced the development status of the first scale optical metrology station of the science, technology and industry for national defense in metrology of basic physical quantities of optical imaging and optical radiation, comprehensive parameters metrology guarantee of weapons and photoelectric equipment, optical frontier technology metrology and development of military photoelectric testing equipment. The main problems of national defense optical metrology and its future development trend were also proposed.
The foreign new-type gimbal mount of airborne optoelectronic platform and its key technologies were reviewed. Combined with the development trend of equipment products of airborne optoelectronic system, the technical status of gimbal mount platform was described, and the configuration, vibration isolation form and stability accuracy were introduced. From the aspects of task integration, high-precision stability and motion compensation, the requirements of airborne optoelectronic system on gimbal mount platform, such as larger space for task sensor layout, stronger motion compensation function and higher stability of ring frame were analyzed. The foreign new-type unconstrained driving-active following and parallel-type active following gimbal mount platform innovative technologies were researched. The results show that the foreign new-type gimbal mount of airborne optoelectronic platform realizes the stability performance of 3 axis over 5 μrad on the basis of mission load and gimbal mount mass ratio greater than 1. Finally, the key supported technologies of new-type gimbal mount of airborne optoelectronic platform were proposed.
According to the imaging performance requirements of airborne optoelectronic system, starting from the detector pixel size, the influence of detector pixel size on detector performance parameters such as detector dynamic range, signal-to-noise ratio and modulation transfer function was researched. Further the influence of detector pixel size on overall performance parameters of optoelectronic system, such as resolution, signal-to-noise ratio, detection and recognition operating range was analyzed. Finally, the parameters of foreign typical airborne optoelectronic system and the selected detector parameters were listed. Through the analysis of relationship between performance parameters of the detector and overall performance parameters of the system, the suggestions on the selection of the detector pixel size and the typical value Fλ/d of the airborne optoelectronic system were obtained, that is, generally, in order to obtain the long-distance high image quality images, the airborne optoelectronic system gave priority to the large pixel detector, and comprehensively weighed the relationship between detector pixel size and system Fλ/d, so as to control the Fλ/d within 2.
Different from the common missile, the loitering missile can cruise over the target to obtain the target location information and transmit it to the command center, which is used for battle-field situation analysis and optimum assignment of firepower. Limited by the load capacity and cost requirements, the target location ability of the loitering missile is not comparable to that of large unmanned aerial vehicle (UAV). In order to promote the target location accuracy of loitering missile, the error sources were analyzed from the principle and process of the target location of loitering missile. Under typical working condition, the influence degree of primary factors such as longitude and latitude errors of global positioning system, course errors of inertial navigation system (INS), angle measurement errors and ranging errors of rangefinder on target location accuracy were studied, which could be used as the design basis to promote the target location accuracy. According to the influence of longitude and latitude errors of global positioning system on target location accuracy, the outfield test was carried out to verify the above analysis conclusions. The results show that as the longitude and latitude accuracy of the global positioning system varies from 5 m to 1 m, the circular probable error (CEP) of target location reduces by about 31.5%, which is consistent with the theoretical analysis.
The photoelectric reconnaissance equipment is widely applied in ground target reconnaissance of small and medium-sized UAV. In order to realize the single-station passive location to ground target by UAV photoelectric equipment without the laser ranging information, the method of single-station passive location based on the virtual ellipsoid was proposed, and the model of single-station passive location to ground target was constructed. In the principle of intersection of space rays and virtual ellipsoid, the geodetic coordinates of the targets were obtained in real time by resolving the equivalent azimuth and pitch, estimating the target altitude and resolving the target location. The simulation results show that, under the condition that the altitude estimate error is less than 500 m, the method of single-station passive location can realize the three-dimensional target location with the location accuracy of longitude and latitude of 10−3 ° and the altitude location accuracy of 150 m, the relative location with higher than 50% degree of confidence and better than 10% R passive location accuracy can be realized.
The vibration of the equipment ring frame will be caused by the interfence factors of aircraft combat environment of airborne photoelectric stabilized sighting platform, which has a great influence on the stability and tracking accuracy of load optical axis of photoelectric platform. The main task of vibration reduction is to effectively isolate the ambient vibration. Compared with the traditional rubber shock absorber, a new flexible vibration reduction design of airborne photoelectric stabilized sighting platform was proposed. The modal simulation analysis of the new vibration reduction model was carried out by ANSYS simulation software. Finally, the performance of the design was evaluated effectively by vibration test. The error between the test results and the simulation evaluation is 0.56%, which shows that the design has the ability of vibration reduction to airborne photoelectric stabilized sighting platform.
In order to solve the problem of maintaining the pitch angle and ground horizontal angle in real time during the 360° panoramic scanning of search and track system on the moving base, an automatic leveling control technology was designed. On the basis of rate closed-loop stabilization, the tilt sensor was adopted to constitute the spatial position loop, which formed the double closed loop of position and rate, and the automatic leveling of the system line of sight was realized. Aiming at the automatic leveling technology, the key of platform control, the spatial position loop constituted by the tilt sensor and platform gimbal angle was emphatically analyzed. The relation between line of sight and horizontal plane angle of search and track system was theoretically deduced, and the system control was analyzed and simulated. The final simulation analysis results are basically consistent with the actual test results and meet the index requirements of the system.
The flexure hinge is one of the important components of fast steering mirror (FSM). The impact of its structural characteristic on FSM performance was analyzed to guide the structure design of FSM. The flexure hinge was simplified as an elastic joint, which could be equivalent to triaxial translational stiffness and triaxial rotational stiffness. Based on the Euler dynamics theory, the motion differential equation of a two-axis FSM was derived, and the Simulink model of the FSM control system was established. Under the given vibration condition, the influence of structural resonant frequency on FSM performance was simulated. The results showed that the higher the translational resonant frequency, the higher the FSM lock zero accuracy, and the translational resonant frequency should be more than two times of the gain crossover frequency. Considering the requirements of lock zero accuracy and limitation of the motor torque, the rotational resonant frequency should be from 25 Hz to 50 Hz. Finally, the vibration experiment was carried out. The simulation results are accord with the experimental results, which verifies the correctness of the simulation model.
The system reliability modeling and analysis is the basis of reliability allocation and prediction, fault tree analysis and reliability optimization design. A reliability modeling and analysis method for electro-optical system was introduced. For some subsystems with multiple failure modes following exponential distribution, according to the homogeneous Markov stochastic process theory, a reliability model was built using the Markov state transition diagram method. Then the analytical expression, numerical calculation method and Monte Carlo simulation method were presented. The reliability model was applied to an example analysis for power supply circuit of an airborne electro-optical system. The above methods were used to calculate, and the results were compared and analyzed, which verifies the correctness and feasibility of the proposed method.
The target location accuracy is an important index to evaluate the performance of airborne electro-optical system. For the high-altitude airborne electro-optical system, the target location accuracy is not only affected by the comprehensive factors such as sensor, rangefinder, stabilization accuracy of load platform, stabilization accuracy and position accuracy of flight platform, but also affected by the atmospheric refraction. For the long-distance ground observation of high-altitude airborne electro-optical system, the impact of atmospheric refraction on target location is particularly serious. Starting from the influence mechanism of atmospheric refraction on target location, an atmospheric model was given to analyze the influence factors of atmospheric refraction. Based on the earth model between the sphere and the reference rotating ellipsoid, the atmospheric refraction error model was given. Finally, the influence of atmospheric refraction on target location was analyzed according to the proposed earth model of approximate reference rotating ellipsoid. The analysis results have important guiding significance for the atmospheric refraction correction of airborne electro-optical system for long-distance target location.
The stabilization accuracy is the key indicator to measure the performance of electro-optical platform, the disturbance torque has the greatest influence on the stabilization accuracy, and the cable elastic moment is an important component of the disturbance torque. Therefore, reducing the cable elastic moment is of great significance to improve the stabilization accuracy of the electro-optical platform. The mathematical model of electro-optical stabilized platform and cable elastic moment were established and the influence of elastic moment on stabilization accuracy was quantitatively analyzed. On this basis, a method to reduce the cable elastic moment was proposed. By applying this method to actual products, the results prove that the method can reduce the elastic moment by 0.180 N·m and decrease the angle change of optical axis by 16.3%.
Aiming at the urgent requirements of military photoelectric system for field of view, image quality and system miniaturization, a large-aperture off-axis three-mirror optical system was designed according to the index requirements. The off-axis multi-mirror structure was adopted to eliminate the system obstruction and reduce the structure size. By introducing the complex profiles, the large-aperture design was realized. While ensuring the sufficient resolution, the field of view angle of the optical system was increased to obtain richer target features and improve the target detection and recognition ability of the system. Compared with transmission-type structure and foldback system, it greatly reduced the volume and weight of photoelectric products and effectively reduced the load of servo design, which had the characteristics of good concealment, wide spectrum coverage, high transmittance and strong field of view compatibility. According to the design results, the full field of view modulation transfer function (MTF) of TV optical path is higher than 0.2 at 120 lp/mm, the MTF of SWIR optical path is higher than 0.3 at 60 lp/mm, the MTF of MWIR optical path is higher than 0.15 at 30 lp/mm, and the grid distortion is less than 0.5%, which meet the design index requirements.
In order to solve the simulation problem of beam pointing in a wide range during the tracking accuracy measurement of photoelectric tracker, a two-dimensional fast steering mirror (FSM) with large aperture and high accuracy was designed. An elliptic and microcrystalline plane mirror was designed with long and short axes of 230 mm and 160 mm respectively, and the surface accuracy was better than λ/30. Driven by the voice coil motors and supported by the flexible support hinges and DSP embedded control system, the swing angle range was ±30 mrad, the motion control accuracy was 5 μrad, the motion control linearity was better than ±0.20%, and the angular resolution was better than 1 μrad. Through the software control, the circular, linear and random motion of the incident beam could be simulated. Finally, the design indicators were tested, which could meet the requirements of tracking accuracy dynamic beam simulation.
To improve the recognition and classification ability of electro-optical system for dim and small targets, and reduce the dependence of algorithms on hardware platforms and data, an unsupervised classification method was proposed, namely the fine-grained classification method based on deep features clustering. Firstly, the targets were suggested by the extraction of shallow features such as contour, color and contrast. Then, after a super-resolution processing, a convolutional neural network was used to encode the deep features of the target. Furthermore, the principal component analysis based on attention mechanism was adopted to generate the characterization matrix. Finally, the clustering method was used to realize the fine-grained target classification. The experiments were set to verify the classification performance of the deep clustering method based on different neural networks on different data sets. The fine-grained classification performance based on ResNet-34 clustering method reached 92.71% on CIFAR-10 test set. The results show that the fine-grained target method based on deep clustering can achieve the same effect as the strong supervised learning method. In addition, the classification effect of different fine granularity can be realized according to the different numbers of cluster and selection of cluster grades.
Aiming at the real-time requirements of image fusion in the infrared and visible light, a real-time implementation method to solve the current high-definition or ultrahigh-definition multi-source Laplacian pyramid image fusion was proposed. Based on the video data stream, a parallel processing pipeline architecture of Laplacian pyramid system was designed. The time delay and optimization ideas between the pipelines were analyzed. All the delay time differences were compensated through on-chip cache to achieve the equal length of pipeline and guarantee the integrity of data processing in the whole algorithm. This method could realize 5-level Laplacian pyramid fusion of dual-channel 1080×1920@60 Hz video images on XILINX 7 series field programmable gate array (FPGA) and above. The experimental results show that this real-time method has better fusion effect, with only 10.535 ms of one-frame image fusion and the processing delay is less than 1 ms.
The deep learning has developed rapidly in the field of detection, but limited by the training data and computing efficiency, the intelligent algorithms of deep learning are not widely used in the edge computing field based on embedded platform, especially in real-time tracking applications. Aiming at this phenomenon, in order to meet the needs of domestic and intelligent technology at the present stage, an improved twin network deep learning tracking algorithm was implemented. The fine-tuning network was added to the feature network to solve the problem that the network model could not be updated online and improve the accuracy of tracking. The center distance penalty term was added into IoUNet loss function to solve the problems of position jumping, existence of convergence blind area and the slow convergence when IoU was the same. The trained network was pruned through channels to reduce the size of network model and improved the loading and running speed of the model. Finally, the model was implemented in real-time on Huawei Atlas200NPU platform. The proposed algorithm accuracy is up to 0.90 （IoU>0.7）, and the frame rate reaches 66 Hz.
The stabilization accuracy is one of the key performance indicators of electro-optical pod, and the research on the measurement of line of sight stabilization accuracy is significant for the measurement and acceptance of electro-optical pod. Combined with coarse and fine platform stabilization of electro-optical system, a measurement method of stabilization accuracy based on time/frequency domain analysis was proposed. By collecting the data of inertial angular-rate sensor and optical compensation elements under random vibration environment, the angular rate, image jitter and probability distribution of image drift were obtained based on the signal time-domain analysis. Based on the signal frequency-domain analysis, the power spectral density of line of sight angular position signal was obtained. The frequency band stabilization accuracy contribution was proposed, which could evaluate the influence degree of different frequency bands on stabilization accuracy. The efficiency improvement with two-level stabilization was used to evaluate the improvement degree of two-level stabilization in different frequency bands on system stabilization performance. This method can intuitively reveal the image jitter and probability distribution, and give the frequency factors affecting the stabilization accuracy of line of sight, which has important engineering application value for guiding the design of electromechanical system.
The brightness is an important parameter of photometric characteristics to characterize the luminescent materials. A design method of ultra-low brightness meter was proposed, and the working principle and composition of the device were described. The automatic measurement of ultra-low brightness was realized by using the technologies of weak light signal processing, nonlinear calibration, cooling and heat dissipation. According to the principle of brightness meter measurement, the calibration was carried out, and the uncertainty of measurement was up to 5%. The ultra-low brightness meter can be used in testing sites such as laboratory and field, which can provide metrological guarantee for performance evaluation and calibration of low-level-light night vision equipment, display system, special light source and luminescent materials.
The Ritchey-Common method is one of the main methods to measure the large-aperture flat mirror with small-aperture interferometer. By analyzing the influence of radius of spherical reference mirror, position of flat mirror and error of Ritchey angle on the measurement accuracy in this method, the selection method of the three-parameter was given. Aiming at the inefficient measurement caused by error separation in Ritchey-Common method, a rapid Ritchey-Common measurement method during processing was proposed. The influence of positioning errors such as position and angle of the measured flat mirror on the measurement results was simulated, and the experiments were carried out. The maximum deviation peak-valley value (PV) between this method and the direct measurement method is 0.015 1 μm, and the root-mean-square (RMS) is 0.003 6 μm, which can effectively meet the needs of rapid surface measurement in processing.
In order to obtain the real optical characteristics of digital micro-mirror devices (DMD), a test method for the reflection characteristics was proposed, and an experimental device was built to test the relative reflection efficiency of digital micro-mirror devices. Firstly, the test optical path was built. Then, the optical path was used to measure the spot energy distribution curves received by the camera when the digital micro-mirror device and the aluminum mirror were used as the reflecting elements respectively, and the curves were integrated. Finally, the relative reflection efficiency of the digital micro-mirror device was obtained by dividing the integral values obtained under the two test conditions. The test results show that the relative reflection efficiency of the digital micro-mirror device is 45.33% when using a 632.8 nm wavelength laser as the light source and 71.75% when using the white LED as the light source. After many tests, it is found that the repeatability precision of the two test modes is about ± 5%. The above test results can be used as a reference for the calculation of energy transfer efficiency and device selection when using digital micro-mirror devices to develop related instruments in the future.
With the development and application of infrared (IR) imaging technology, the IR imaging simulation and its validation methods have been paid more and more attention. The existing validation methods of IR imaging simulation model rarely take the impact of human vision into account, which will lead to the serious consequences. In order to solve this problem, the validation method of IR imaging simulation model based on the recognition range was proposed. With the recognition range as the accuracy evaluation factor of IR imaging simulation model, the comprehensive differences of various aspects such as gray level distribution, signal-to-noise ratio (SNR) , resolution, imaging size and human vision between the simulated image and the measured image could be evaluated.
In the process of assembling and adjusting the infrared optical lens group, the optical center-deviation will occur. Since the infrared material is not transparent to visible light, the traditional visible light adjustment mode cannot be used, which becomes a difficulty in the assembly and adjustment of the infrared lens group. An assembly and adjustment scheme based on the OptiCentric dual-optical path center-deviation measuring instrument from TRIOPTIC company in Germany was proposed, and introduced in detail the assembly and adjustment methods of no-mirror seat centering method, the mirror seat method and the aspheric surface. The advantages and disadvantages of the no-mirror seat centering method and the mirror seat method were analyzed. In addition, it was pointed out that there were still some limitations in the centering of aspheric surfaces using the OptiCentric center-deviation measuring instrument. Finally, the optical transfer function tester was used to test the lens adjusted by the above two methods. The test results show that the lens adjusted by the center-deviation measuring instrument can meet the requirements of technical indicators.
During the continuous launching of gun, the temperature of inside wall of gun bore increases substantially, which will cause a high security risk when the temperature exceeds the ignition point of all combustible cartridge. An application and device of infrared thermal imaging technology in gun bore temperature measurement was introduced, included the composition and temperature measurement principle of the device. Combined the course of replacing ammunition during the continuous launching process, the image processing techniques such as edge detection, contour extraction, and identification judgment were used in the gun bore temperature measurement device, it could automatically analyze the effective time and the target area of temperature measurement. Based on the resolving curve calibrated by least-square method, the maximum temperature and average temperature of the target area could be determined, and the device reported the temperature data to the gun control system in real time for it to determine whether to replace ammunition or strike, which could effectively improve the safety of gun during the continuous launching process.
The infrared radiometer is generally used for the calibration of the infrared thermal imager testing equipment. A measurement module and method for infrared radiometer were introduced. A measurement scheme of sample and hold was designed, the sampling pulse was generated from the reference signal, and the sampling point was set at the 1/4 phase of each signal period, which could significantly improve the measurement ability of weak signals. For the black-body radiation signal at 35 ℃, the measured signal strength could be increased by 57.6% by comparing with the existing scheme. Under the condition that the background temperature of the infrared thermal imager testing equipment was 22 ℃, the measurement signal accuracy could be improved by more than 50% through the comparison test with the existing instruments.
The metasurfaces have the ability to precisely and efficiently manipulate the light wave at sub-wavelength scale. However, there are still many technical difficulties to be overcome when it comes to the realization of active control separately. The combination of liquid crystal (LCs) and metasurface is expected to give full play to their respective advantages to achieve a new type of active optical control device with high resolution, large diffraction angle and ultra-compact structure. The independent functional design of LC and metasurface was taken as the classification basis to review the research progress of active LC metasurfaces in recent years, which specifically included the combination of LC wave plate and polarization-sensitive metasurfaces, the combination of LC environment and resonant metasurfaces, and complementation of optical properties with LC and metasurface. Finally, the challenges and development prospects of active LC metasurface were discussed and prospected.
The diffractive optical elements (DOE) have great advantages in correcting chromatic aberration compared with spherical and aspheric optical selements, especially in the field of infrared optics, the application of DOE can further increase the design freedom of optical systems. With the further expansion of infrared optics market, the conventional single point diamond turning technology of diffraction optics is difficult to meet the large-scale demands, so the precision molding technology has become the key technology to solve the above problems. The mold design is one of the key points of precision molding. In order to reduce the mold design cycle, the pre-design and pre-correction of mold were carried out by using the finite element simulation method, and then the mold was processed. The single-station precision molding machine was adapted for precision molding test of designed molds. The test results show that, with the reasonable process parameters, the PV value of the surface shape accuracy of DOE can reach 0.56 μm, the position error is less than 0.011 mm, and the height error of the band is less than 0.12 μm, which verifies the effectiveness of the simulation pre-compensation in the design of diffractive optical molds.
In order to meet the aerodynamic requirements, the dome or optical window with conformal thin-walled structure has become the development trend of high-speed aircraft in the future. However, the cutting force will change with the axial position in the machining process of such parts, and one-time machining is difficult to meet the accuracy requirements. It is necessary to control the surface error caused by the change of cutting force by on-machine measurement and compensating machining. Taking the ultra-precision lathe as the motion platform, the on-machine measurement system was designed for thin-walled optical parts with high steepness, the optimization algorithm was studied for the distribution of measuring points, and the measuring efficiency and accuracy were realized at the same time. The correction model for thermal deformation error was established to improve the accuracy of on-machine measurement for thin-walled optical parts with high steepness. The on-machine measurement was used to provide guidance for compensating machining of a thin-walled dome, the surface error was reduced from PV (peak to valley) 3.1 μm to PV 0.7 μm, the coaxiality is controlled to 1.02 μm, and the performance requirements are satisfied for optical system.
In the field of optical fabrication, the power spectral density (PSD) is used to characterize the error spectrum. However, the PSD is the statistical information of surface error, which is not as intuitive as peak-valley (PV) and root mean square (RMS). In order to analyze the relationship between PSD and process parameters, based on the definition of PSD, the influence of different parameters of random surface contour on optical PSD was analyzed, and summarized the key control points of PSD. Then, the PSD curves processed under the typical paths of numerical control polishing were analyzed on flat glass. The results show that the PSD is correlated with the amplitude and frequency distribution of random contour, and the phase has almost no influence on it. When the RMS is close, the slope of PSD linear fitting and RMS Slope decreases with the increase of the auto-correlation length of the random profile. The short-range machining path can effectively suppress the peak value of PSD curve compared with the long-range ordered path, which makes the optical element meet the requirements of spectrum suppression.
In order to meet the requirements of high-precision alignment and positioning of optical elements for two-mirror reflection system, as well as the requirements of reliability and efficiency for system engineering applications, an adaptive alignment technology based on artificial neural network (ANN) was proposed. Based on the vector wave aberration theory, the mapping relationship between the wave aberration and the offset of the two-mirror system was analyzed. The ANN was built under the framework of Keras, and the adaptive alignment model was constructed with non-analytic ideas. An adaptive alignment device was developed to make the alignment accuracy of the secondary mirror better than 2 μm, and the tilt alignment accuracy is better than 2″, which solved the technical problems such as algorithm design and precision optimization, micro-stress connection of mirror group, and completed the adaptive alignment verification of a double parabolic defocusing system. The test results show that by using this technology, the wave aberration after alignment of system is better than λ/16, the alignment cycle is greatly shortened, and the assembly reliability passes the environmental test assessment, which lays a foundation for the engineering application of the technology.
The electro-optical searching and tracking system is a kind of kernel electro-optical device for battlefield situation awareness, information acquisition, target capture as well as tracking and positioning, and its tracking accuracy is the key parameter to represent the combat capability of the system. According to the measurement requirements of this parameter, a design scheme of collimator array target simulator based on OLED was proposed. The simulated angular velocity range of dynamic target is 1°/s~100°/s, and the angle positioning accuracy is 0.8″. Through the analysis of angular velocity simulation of dynamic target simulator, the relative expanded uncertainty can reach 0.6%~0.8%.
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.
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.
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.
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.
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.