2019 Vol. 48, No. S1
2019, 48(S1): 1-5.
doi: 10.3788/IRLA201948.S106001
Laser systems often cope with complex ambient air flow. As the size of the laser beam expanding system increases, its crystal window is difficult to achieve. Then the ambient air flow can easily enter the system, thus it affects the beam quality. CFD was used to solve the problem of aero-optical effects caused by ambient air flow. With the aid of fluid mechanics software FLUENT CFD model, the internal flow field of the laser beam expander was simulated. Various parameters of the internal flow field of the system were obtained under different inlet angles. Through the Gladstone-Dale relationship, the refractive index could be calculated from the flow density field. Using the ray tracing method, the beam transmission path could be got in the non-uniform refractive index flow field. Finally, the optical aberration caused by turbulence was calculated by numerical analysis. The results show that the ambient airflow will introduce more vortices to the flow field of the primary mirror, the secondary mirror and the deflecting mirror. The influence of the optical effect cannot be ignored, which must be considered in the overall design. Therefore, a method to increase the length of the mirror tube of the beam expanding system was proposed to reduce this effect. After the length of the mirror tube was lengthened by 0.5 m, the eddy current in the beam expanding system can avoid the main path of beam propagation. Meanwhile, the RMS can be reduced from the 0.317m to about 0.078m. The study proves the necessity of avoiding the aero-optical effect caused by ambient airflow. And it provides reference data and ideas for the optical and structural design of the beam expanding system.
2019, 48(S1): 6-14.
doi: 10.3788/IRLA201948.S106002
Laser ablation driven is one of the most promising active debris removal technologies. However, the rotation state of the target has a very complicated impact on the effect of laser ablation, which is one of the problems to be solved. In this paper, the laser driving impulse under the continuous irradiation for rotating plate target was analyzed by theoretical calculation, and the effect of pulse frequency and target rotation speed on it was also discussed. And with the surface triangulation and three-dimensional reconstruction calculation method, the magnitude and direction of laser driving impulse under the continuous irradiation for rotating typical shape target, such as cylinder, cuboid and cone, and irregular shape target were analyzed under different pulse frequency and different rotational angular velocity. The results show that the rotation of the target will make the driving effect of continuous pulse laser change periodically with the increase of pulse number; Its magnitude and periodic variation are affected by the rotation speed, pulse frequency and the shape of itself; By the rational selection of laser irradiation strategy, the influence of rotation on the impulse direction of laser pulse continuous irradiation can be minimized or eliminated.
2019, 48(S1): 15-20.
doi: 10.3788/IRLA201948.S106003
The temperature stability of the vapor cell plays an important role in improving the performance of the nuclear magnetic resonance gyroscope. It's meaningful to explore an approach for temperature stabilization of the vapor cell based on the light intensity of nuclear magnetic resonance gyroscope's probe laser. The negative correlation between the light intensity of the probe laser and the temperature of the vapor cell was analyzed theoretically. Then the concrete corresponding fitting curve about temperature and the light intensity was obtained experimentally. Furthermore, a LabView program for the feedback control of the temperature was designed, which achieved the temperature stabilization of the vapor cell. Finally, the experimental results validated the proposed approach in stabilizing the temperature of the vapor cell, which had advantages of high sensitivity and accuracy. The achieved long-term temperature drift is within 0.02℃/h.
2019, 48(S1): 21-26.
doi: 10.3788/IRLA201948.S106004
A high integration density front-end readout circuit(ROIC) was presented and designed in allusion to the kind of light laser detection and ranging(LiDAR) using avalanche photodiode(APD) detector. The front-end readout circuit consisted of high-gain broadband transimpedance amplifier (TIA), fixed gain voltage amplifier, high-speed real-time comparator, low voltage differential signaling (LVDS)output interface et al. TIA adopted resistance feedback structure. The output voltage signal of TIA connected to next stage through the way of pseudo-difference signaling, therefore obtaining better anti-interference ability. Fixed gain voltage amplifier was a non-inverting amplifier with resistance feedback network. Then a decompensated open-loop amplifier was used for the comparator in the chip. The ROIC can connect with FPGA directly profiting from the LVDS, again improving the integration density of the chip. The circuit was designed with chrt 0.18 m process. The area of chip was about 0.9 mm1.9 mm. The voltage of the power supply to the chip was 3.3 V. Through the test, the gain of TIA can achieve 83.6 dB, the bandwidth can reach 120 MHz. At the same time, the whole readout circuit can make an immediate response for input pulse signal with 5 ns pulse width. The LVDS which was designed as the output of whole readout circuit can meet the request of FPGA's interface.
2019, 48(S1): 27-34.
doi: 10.3788/IRLA201948.S106005
For stainless steel-carbon steel sector laminated plates, the laser concentric circular scanning method was used to bend the plates. The geometrical characteristics measurement of deformed sample were measured by laser scanner. The bending angle of each position of the laser scanning lines and the deformation characteristics of the curved surface on both sides of the scanning line were analyzed. The effects of laser processing parameters and sheet geometry parameters on laser arc scanning bending of sector laminates were studied. The results show that deformation zone of the scanning line after laser circular scanning is three-dimensional curve in space and the bending angles at the scanning line are different. The angle in central line is the smallest and increases gradually to the left and right sides of the plate, reaching the maximum at the edge of the plate. The angle is basically symmetrical along the center line of the plate; The surface is obviously deformed by a curved surface and the area from the scanning line to the outer circular line of the sector plate is inwardly recessed, and the area from the scanning line to the inner circular line of the sector plate is convex outward. The research results provide a basis for in-depth understanding of the three-dimensional deformation mechanism of laser circular scanning.
A comprehensive study of coherent coupling of low-amplitude spatial solitons that co-propagate in biased photorefractive crystals with both the linear and quadratic electro-optic effects was presented. Our results were shown that coherently coupled bright-bright and dark-dark spatial soliton pairs in the low-amplitude regime could be formed under appropriate conditions. The evolution equations, analytic solutions and the expressions of soliton pair widths of these low-amplitude coherently coupled spatial soliton pairs were obtained. It was proven that the existence, property and propagation of these soliton pairs due to co-effects of both the linear and quadratic electro-optic effects was greatly influenced by the photorefractive effects which could be enhanced, weakened or even counteracted because of the interaction of these two electro-optic effects. Moreover, the effects of three physical factors, i.e., the initial phase difference between two incident coherent beams, the intensity ratio and various external bias field on the existence conditions, properties of these low-amplitude coherently coupled soliton pairs have been discussed in detail. Finally, the self-deflection of low-amplitude bright-bright soliton pairs had also been investigated by means of perturbation procedure.
2019, 48(S1): 43-49.
doi: 10.3788/IRLA201948.S106007
Atmospheric aerosol, a main pollutant source, mainly exists in planetary boundary layer, and the precise detection of its vertical distribution, especially in the near ground, has an important application value. Backscattering lidar is a powerful tool for aerosol extinction coefficient profile detection, but no signals or only weak signals could be received in near distance because of the blind zones and transition regions. The above problems were resolved by combining CCD detection with backscattering lidar, and the aerosol extinction to backscattering coefficient (lidar ratio) was retrieved accurately with the combined measurement of Raman scattering channel. In order to validate CCD detection, two different CCD lidars with different CCD position distance and focal length were designed respectively for comparison. The relative difference of aerosol extinction coefficients from two CCD lidars was less than 3% under about 1.2 km height, which indicates that the detection results are in good agreement. Case study shows that aerosol extinction coefficient near the ground is inhomogeneous with height, and sometimes increases with time and sometimes decreases.
2019, 48(S1): 50-55.
doi: 10.3788/IRLA201948.S105001
By combining a large mode area(LMA) Yb-doped double cladding fiber(YDCF) amplifier with a solid state seed laser, an fiber amplifier, whose single pulse power was about 1 mJ and narrow linewidth was about 0.1 mJ, was reported. Different from the traditional one-stage fiber amplifer with solid state laser seed source, a two-stage large diameter fiber amplifer was used in the YDCF amplification system. The two-stage fiber amplifer was much simpler in the aspect of coupling the spatial seed light into the fiber. A variety of methods were used to suppress nonlinear effects during the amplification process. Obvious nonlinear effects such as SBS, SRS, were not observed in the output, with the SNR exceeding 30 dB. After YDCF amplification system, the output average power was amplified to 10.07 W. Compared to the power of seed, which was about 0.38 W, the output was increased by 14.23 dB. At the pulse repetition rate of 10 kHz, the pulse energy is about 1 mJ, with the pulse width of 50 ns. The beam quality M2 of the output laser is 3.72. The pulsed fiber amplifier with narrow linewidth and high pulse energy will be very useful in many practical applications, such as laser remote sensing, laser measurement and nonlinear frequency conversion and so on.
2019, 48(S1): 56-63.
doi: 10.3788/IRLA201948.S105002
Based on the three-level rate equation, a simulation model of the end-pumped K vapor laser threshold was established, and the threshold characteristics of diode pumped K vapor laser was analyzed. The influences of operation parameters on the threshold pumped power intensity were investigated, which was based on this model. The result shows that cell's temperature and length both govern the distribution of populations of K, thus combining to impact on the threshold pumped power intensity, and there exists optimal temperature and length. The threshold power intensity linearly increases with pump linewidth. The buffer gas pressure impacts on the threshold intensity by changing the cell's absorption efficiency of the pumped power. High window transmittance and less than 70% output coupling can make threshold keep in a lower level. The study for various parameters of components will provide reference for the design and optimization of the systems, and diode pumped potassium vapor laser output.
The accelerated aging test of 60 W(CW mode) 808 nm indium-packaged conductively cooled single bar high power semiconductor laser with constant current under three different temperatures was analyzed by Weibull and Log-normal distributions models, respectively. The characteristic lifetime and statistical average lifetime of the device under all the tempertures including room temperature were calculated in Weibull distribution analysis, and it is found that for early failure test, the shape parameter is less than 1, and the calculation error of mathematical average lifetime is larger, which is not as good as statistical average lifetime. In Log-normal distribution analysis, the medium lifetime and statistical average lifetime under all the tempertures are calculated. It is found that for early failure test, the logarithmic standard deviation is larger and creates larger error of statistical average lifetime. It means that Log-normal distribution mode is not suitable for lifetime estimation of early failure device. Finally failure analysis of accelerated lifetime devices is carried out.
2019, 48(S1): 72-77.
doi: 10.3788/IRLA201948.S117001
The structure of the payload adapter was becoming more and more complex to meet the needs of the new spacecraft. In order to offset the large deviation of the center of mass of a reentry spacecraft and realize the self-leveling of separation design, a payload adapter with irregular shape was designed according to the structural characteristics of a reentry spacecraft. Based on the analysis of the characteristics of riveting technology and additive manufacturing technology, two different process schemes of riveting and additive manufacturing were compared and analyzed. According to the actual manufacturing precision measurement needs of the payload adapter with irregular shape, laser tracking measurement technology was selected as the precision measurement method. Through the application case analysis of axis measurement after the installation of a certain type of upper-stage engine nozzle, it can be seen that the measurement and data processing method based on laser tracker and least square method could be applied to the payload adapter with irregular shape. And the obtained accuracy data could be used as the basis for the separation of spring selection in the subsequent separation design.
2019, 48(S1): 78-82.
doi: 10.3788/IRLA201948.S117002
The low light level camera (LLLC) can acquire images of Visible/Near Infrared (VIS/NIR) targets in large dynamic range which are from daylight to starlight conditions. Accurate radiometric calibration for the LLLC was a key part of determining the performance of the camera, and it's very important to the quantitive application of images. The output radiance of the uniform light source which is used to calibrate the LLLC should be in the range from 110-9 W/(cm2sr) to 310-2 W/(cm2sr). For realizing high-precision radiometric calibration, a uniform light source which had constant spectrum in each output level was designed. A three-integrating-sphere transfer design was adopted and the difficulty of constant spectrum for each output level of the light source over multiple orders of magnitude was overcame. The design of the uniform low light level source for radiometric calibration was introduced. Furthermore, the accuracy of spectral radiance measurement for such a large dynamic range light source was also a challenge. The spectral radiance of each output level of the light source was obtained by transfer measuring method. The result of radiometric calibration for large dynamic range LLLC was given. The uncertainty of radiometric calibration for the LLLC achieved 18% (k=2).
2019, 48(S1): 83-88.
doi: 10.3788/IRLA201948.S117003
Based on aerosol data measured at sea from August 2004 to December 2016, the variation of aerosol particle number concentration and particle size distribution dependent on meteorological conditions was studied. Aerosol data were measured in the offshore sea of Maoming, Guangdong as well as the Pacific Ocean and the Indian Ocean. There were two parts included in the data:(1) the particle number of atmospheric aerosol measured by the Optical Particle Counter (OPC); (2) it was measured that atmospheric temperature, relative humidity, air pressure, wind speed and other meteorological parameters by Forain Weather System etc.. The variation of particle size distribution on different meteorological conditions was analyzed, i.e. the variation of particle size distribution was simulated under different relative humidity and wind speed following by the value of theoretical analog was compared with that of actual measured. The results show that, on the one hand, it is realistic to retrieve the influence of relative humidity on particle distribution by using the model of r(RH)/r=(1-RH)-1/3.9. On the other hand, it is reasonable to utilize the model of lgN=aU+b to retrieve the effect of the wind speed on particle size distribution. There is an important guiding significance for the establishment of ocean atmospheric aerosol model.
2019, 48(S1): 89-96.
doi: 10.3788/IRLA201948.S117004
Rotary inertia, damping coefficient and stiffness are closely related to the inherent characteristics of rotary inertial stability platform(ISP). The genetic algorithm(GA) is used to identify these three parameters. Based on the theoretical analysis, the model of ISP was established, and the whole process of parameter tuning was designed based on GA. The Matlab/Simulink was used to verify the parameter tuning accuracy of GA. The results show small deviations exist between the parameters of the tuned parameters and the set value, and the accuracy is close to that of the parameter tuning at the stage. A series of experiments were carried out to validate the parameter tuning accuracy of GA. The experimental results show that the method can identify rotary inertia, damping coefficient and stiffness of rotary inertial stable platform with high accuracy and the effectiveness of parameters tuning method presented in this paper are validated.
2019, 48(S1): 97-103.
doi: 10.3788/IRLA201948.S117005
Micro-impulse measuring system is the essential experimental support for pulsed micro-thruster development. An universal design method of micro-impulse measuring system based on pivots was put forward. Firstly, based on the second-order vibration system of micro-impulse measurement model, the basic design conditions were brought forward:the impulse measuring range and the corresponding error range, the measuring error range, the displacement sensor range and the corresponding error range. Secondly, according to the relationship between the impulse and the response, the torsional angle measuring method based on the displacement sensor and the impulse instantaneous impacting model, the constraint conditions of the system parameters, such as the measuring arm, the force applied arm, the torsional spring and the moment of inertia, were analyzed. Lastly, the design steps were given according to the relationship between the basic design conditions and the system parameters. The design method is appropriate for the impulse measuring system design for any pulsed micro-thruster, and has good universality and practicability.
2019, 48(S1): 104-113.
doi: 10.3788/IRLA201948.S117006
In order to realize stereo vision localization for mobile robot with high efficiency and low cost in the automated factory, a stereo vision localization method for mobile robot based on auxiliary target was proposed. Firstly, background subtraction based on Gaussian mixture model and morphological methods were used to detect motion areas of mobile robot from video images. Secondly, feature points in motion areas of mobile robot were extracted by the FAST algorithm. On this basis, by analyzing three-channel color characteristics of neighborhood pixels on each feature point, four vertices of the square auxiliary target fixed on the mobile robot were screened from extracted feature points. Finally, the 3D coordinate for localization of mobile robot was calculated with intrinsic and extrinsic parameters of binocular cameras calibrated. Experiment results show the feasibility and validity of the proposed method, which has the advantage of small algorithm complexity and high real-time.
2019, 48(S1): 114-119.
doi: 10.3788/IRLA201948.S117007
A CO concentration analysis system for natural gas was developed based on the diffuse absorption band of CO gas molecules at 1.56 m, combined with wavelength modulation and harmonic detection techniques. A long light path gas absorption cell was used to analyze CO concentration. The system was mainly composed of laser driving module (voltage-controlled constant current source and temperature control circuit) gas chamber of gas absorption cell and phase-locked amplifying circuit and other signal processing modules. A hybrid simulated gas station developed by the laboratory was used to simulate the natural gas background with different standard concentrations of CO gas. The experimental results show that the minimum detection limit of the system is up to 5.6 ppm; the relative error of CO gas with 0.05% concentration is less than 2; and the relative error is less than 1.8% for standard CO gas with 10% concentration. When the range of CO concentration is 0-100 ppm, the detection sensitivity is 0.09 mV/ppm. Compared with the CO detection system of the quantum cascade laser, the system has the advantages of high performance-to-price ratio, suitable for complex oil and gas development, and has great application value in the field of petroleum, chemical and natural gas.
2019, 48(S1): 120-125.
doi: 10.3788/IRLA201947.S117008
In order to solve the problem of orbit transfer of the nano-satellite under the action of micro-thrust of laser micro-thruster, a simplified semi-major axis calculation method for in-plane orbit transfer under the tangential thrust was proposed by using perturbation equation. The influence of the main perturbation factors such as the non-spherical perturbation, the atmospheric perturbation and solar pressure perturbation on the method was analyzed. And the orbital changes of the direct integration of the motion equation under various perturbations were compared with the results from the simplified method. The validity and application conditions of the simplified method was verified. The simulation results show that the orbit maneuverability for nano-satellites can be obtained by simplified calculation method under the tangential thrust of the order of 100N at orbital altitude above 300 km. What is more, for nano-satellite mission design stage, the solar pressure perturbation can be ignored, the atmospheric drag perturbation can be ignored above orbital altitude of 500 km, and the influence characteristics of non-spherical perturbation are similar to those of other satellites.
2019, 48(S1): 126-134.
doi: 10.3788/IRLA201948.S117009
Satellite laser altimetry can quickly and efficiently obtain the 3D coordinate data of ground points with high precision elevation, but the laser was inevitably affected by clouds in atmospheric transmission. Firstly, echo waveforms were fitted according to the echo energy data recorded in the atmospheric transmission process by the geoscience laser altimeter system(GLAS). Secondly, the differential zero-crossing method and Fernald method were used to realize cloud detection and cloud optical depth inversion respectively. Finally, moderate-resolution imaging spectroradiometer(MODIS) data and aerosol robotic network(AERONET) ground station data from Beijing region were employed to perform a validation analysis. The results show that the method presented in this paper has a high credibility in the optical depth inversion of the cloud by laser altimetry satellite. In the actual situation, the cloud optical depth inversion error is less than 0.1, and when the cloud optical depth is less than 1, the relative error is far less than 0.01. The relevant conclusions are of reference value for the quality control of the laser altimetry data of domestic satellites.
2019, 48(S1): 135-141.
doi: 10.3788/IRLA201948.S117010
In order to satisfy the miniaturization, high accuracy and high reliability of spaceborne reflection photoelectric encoder, the signal processing system was designed. Firstly, the overall design of the signal process system spaceborne reflection photoelectric encoder was represented. Then, methods of processing precise code and coarse code were given, and the data processing system was integrated into main system which used FPGA, the size was decreased, at the same time the electric circuit was cold backup to improve the reliability. Finally, 23 surfaces polyhedron and autocollimation were used to test the accuracy. The experiment results show that the resolution is 0.3(22 bit), the primary precision was =2.22(3=6.65), the standby precision is =2.69(3=8.07), by using this signal processing system. By applying to practical projects, the processing system had satisfied the technique reqirement of the spaceborne equipment.
2019, 48(S1): 142-146.
doi: 10.3788/IRLA201948.S117011
Micro-thrust measurement device based on torsion pendulum structure is a common method for micro-thrust measurement of space micro-thruster. Aiming at the calibration problem in micro-thrust measurement, the electromagnetic force constant characteristic based on voice coil motor was studied. The composition and function of the voice coil motor and its calibration application in micro-thrust were introduced. The distribution of magnetic field in voice coil motor and the variation of electromagnetic force under the control factors of coil current, relative distance between coil and magnet were analyzed. An experimental system of constant force characteristics of micro-electromagnetic force was built. Based on the weighing method of high precision electronic balance, the precise electromagnetic force was obtained. With the criterion of electromagnetic force error less than 5%, the stable force output of voice coil motor was obtained, which will lay the foundation for the micro-thrust calibration of torsion pendulum.
2019, 48(S1): 147-151.
doi: 10.3788/IRLA201948.S117012
Optical positioning technology has been widely used in surgical navigation, target tracking and virtual reality systems, in order to improve the accuracy of positioning, many research work has been done on signal measurement and localization algorithms. Using this system, the quality of the light source used for optical positioning was improved by screening near-infrared LED, and the good conditions were created for accurate positioning. The screening detection system consisted of an optical performance detecting section and a high and low temperature testing section. By controlling the rotation angles of the pitch axis and the rolling axis in the turntable, the radiation intensity of the light-emitting elements could be continuously measured by photodetector, the radiation data of near-infrared LED at different rotating faces and different longitudinal angles was obtained, and the half power angle value could be calculated. According to the two important indicators of luminous intensity and half power angle, first, the extreme value data is removed from the selected group; and then two near-infrared LEDs with relative deviation within 5% were selected; and finally the high-low temperature impact test was performed. The selected near-infrared LEDs have stable performance and good luminous consistency, and can be used in groups.
2019, 48(S1): 152-157.
doi: 10.3788/IRLA201948.S121001
The transfer matrix method was used to study and design new optical filters and optical switches with high performance and quality, the modulation of optical transmission characteristics of photonic crystal (AB)5ACn(BABAB)CnA(BA)5 by symmetrical double defects were also studied. The result showed that symmetric double defect one-dimensional photonic crystal (AB)5ACn(BABAB)CnA(BA)5 can achieve the function with high transmission, high quality optical filtering and optical switchings. Besides, with the increase of defect period n and incident angle , the blue shift phenomenon occured when the dual-filter channel moved towards the short wave direction, and the distance between the two channels became shorter, but the speed of blue shift of the two channels was different from that of the two channels. With the increase of defect physical thickness dC and refractive index nC, the photonic crystal dual-filter channel moved towards long-wave direction, resulting in red shift phenomenon, and the distance between the two filter channels increased, the redshift speed of the two filter channels was different from that of the distance between the two channels. With the increase of defect period n, physical thickness dC, refractive index nC and incident angle , the transmittance of the two-channel filter remained unchanged at 100%. The optical transmission characteristics of symmetrical double-defect photonic crystals can guide the research and design of high transmittance, high performance and high quality dual-channel optical filters and high sensitivity optical switches.
2019, 48(S1): 163-173.
doi: 10.3788/IRLA201948.S128001
Typical denoising algorithm were unable to effectively remove the mixed noise of stripe and random noise in infrared images. To solve this problem, an improved NL-means filter was proposed. Firstly, the problem in NL-means algorithm dealing with mixed noise was analyzed, and an experiment was performed to analyze the characteristic of the mixed noise in image patches of infrared images. Based on the experiment results, the mixed noise was modelled using colored Gaussian model, and the ordinary patch similarity index was improved using Mahalanobis distance instead of Euclidean distance, so that it adapts to the local with different complexity in the image. Both simulated and real data experiments show that the algorithm can effectively remove the stripe and random mixed noise compared with traditional image denoising algorithms.
2019, 48(S1): 174-180.
doi: 10.3788/IRLA201948.S128002
The infrared search system has the advantages of not emitting electromagnetic wave, strong anti-electromagnetic interference ability and high precision of target indication, and has a good application prospect in the field of low, slow and small target detection. At present at home and abroad, the target detection algorithm of infrared search system usually extracts the suspected target by using the current image and the background image registration and difference, which is often necessary to save the panoramic background images in the large storage space, and the engineering application of high precision real-time image registration algorithm is also difficult. For the above questions, a infrared low, slow and small target detection method was designed for the infrared search system. Through the processes of morphological filtering, extracting suspected targets with edge detection method, eliminating background interference with target neighborhood eigenvalue statistical method and correlating target information based on multi-frame image, it can effectively eliminate the interference of ground objects, clouds and birds, while accurately detecting the UAV's target in the image. Experimental results show that this method has higher target detection probability and lower false alarm rate than the traditional LCM algorithm. Moreover, it does not involve image difference, and has the advantages of low demand for hardware resources and good real-time performance, etc., and has high engineering application value.
2019, 48(S1): 181-192.
doi: 10.3788/IRLA201948.S128003
Hyperspectral image sparse super-resolution algorithm based on spectral similarity was proposed to improve low spatial resolution of hyperspectral images. The super resolution algorithm, based on the criterion of maximum likelihood estimation and Gaussian mixture sparse representation, assigned various weights to different coding residuals to improve spatial resolution of reconstructed images and the robustness to noise. Based on spectral similarity, the super-resolution model which added sparsity constraints using pixel spectral similarity was proposed to ensure the accuracy of the spectrum images. The experiments have been run to prove that this model achieves a better result than Bicubic, Yang and Pan algorithms in both visual effect and objective measures. Additionally, various parameters in the reconstruction were analyzed in order to provide better image detection and classification.
2019, 48(S1): 193-197.
doi: 10.3788/IRLA201948.S128004
Usually the ability of the space optical camera is degraded by many factors during operation on orbit for the space object observation. The result is induced by variation of some prior parameters such as platform motion, attitude variation, jitter and drift angle during operation on orbit. So it is not satisfying to improve the image quality, only by using the parameters measured on the ground test such as the point response function of the infrared CCD camera. The simulation for the space object observation of the on-board imaging system and the enhancement is proposed here, combining with the information between adjacent spatial and temporal frames. The dynamic model is formulated, representing the characteristic of point response function during multiple exposure times. Furthermore, the enhancement algorithm is proposed based on the correlated information between two adjacent spatial and temporal frames. The norm optimization method is used in the frequency domain. The dynamic point response function of the space object observation system is simulated in the experiment. And the detecting spectrum range is mid-Infrared. The processed result is clear and sharp by the proposed method. The experimental result shows that the proposed method is better than the conventional methods.
2019, 48(S1): 198-204.
doi: 10.3788/IRLA201948.S118001
In order to reduce the range of movement of multi-node laser communication antennas, improve the motion control accuracy of two-dimensional tip-tilt mirror, avoid changing of mirror surface shape caused by the difference material performance between the mirror and the support, a integrated lightweight tip-tilt mirror with a supporting structure was proposed. Integrated design of tip-tilt mirror and support structure was conducted using material of high volume fraction SiC/Al. The thermal and mechanics stability of the mirror surface shape was improved. It can be mounted directly on the elevation axle seat, and the distance between the tip-tilt mirror rotation axis and the surface was shortened to 20 mm. The result of finite element analysis shows that the eigenfrequency of the tip-tilt mirror was of 1 337 Hz. The peak valley value(PV) of tip-tilt mirror surface shape error was better than 0.121, and root mean square value(RMS) was better than 0.031 in the range of (205)℃. Using ZYGO interference to test the mirror surface shape error, test results show that the peak-valley value of tip-tilt mirror surface shape error is better than 0.163 and root mean square value is better than 0.029 in the ambience of (205)℃ Parameter requirement of laser communication antenna for tip-tilt mirror surface shape error /25(RMS) is satisfied.
2019, 48(S1): 205-210.
doi: 10.3788/IRLA201948.S118002
Surface shape accuracy under gravity is an important aspect of space-based mirror performance. A 3 m aperture space-based mirror was optimized based on the parametric model of mirror structure and support point distribution, taking the surface shape RMS under the action of gravity as the object function. Firstly, the number and location of the support points were determined by using the classical theoretical formula, and the structure of the mirror was designed preliminarily. Secondly, according to the lightweight characteristics of the mirror and the kinematics design of the support system, the parameterized model of the mirror structure and the support points' distribution was established. Finally, the process integration and process automation of mirror component optimization were realized by using Isight software, and the relationship between the shape accuracy under gravity and various parameters was studied. The results show that the RMS value of the optimized mirror is 86.7 nm, which is 66.6% less than that of the preliminary design 259.4 nm, and meets the requirements of the project. The proposed optimization method combines with the kinematic model of the support system, and provides a comprehensive and efficient new approach for the optimization of large aperture mirrors with similar lightweight structure and support schemes.
2019, 48(S1): 211-216.
doi: 10.3788/IRLA201948.S125001
Terahertz(THz) waves occupy a very important position in the electromagnetic spectrum. THz technology is recognized as a major cross-cutting frontier in the international scientific and technology community. Photonic generation of THz signal using a recirculating frequency-shifting loop(RFSL) was proposed and experimentally demonstrated. The frequency of optical source was shifted by the RFSL and beats with each other in a high-speed photodetector to generate a THz signal. In the RFSL, the single sideband(SSB) modulator driven by a radio frequency(RF) signal was a key component for frequency-shifting. The frequency multiplication factor(FMF) of the THz signal was controlled by the lap number circulating in the loop. The frequency of the THz signal increased with the improvement of FMF and equals to the frequency multiplication factor multiplied by the frequency of RF signal. Experimentally, tunable signals from 5 GHz to 20 GHz were generated and the FMF was successfully tuned from 1 to 25. The stability of the power and center frequency was detected when the frequency of the signal was 20 GHz. 0.25 THz signal was finally generated by this system.
