2018 Vol. 47, No. 12
column
- Invited paper
- Laser technology and application
- Laser radar technology
- Infrared technology and application
- Photoelectric measurement
- Optical design and simulation
- Photoelectric device and microsystem
- Optical communication and optical sensing
- Laser-matter-interaction
- Physical optics
- Ocean optics
- Structure and control
- Spectrum detection and analysis
- Information acquisition and identification
2018, 47(12): 1202001.
doi: 10.3788/IRLA201847.1202001
Superconducting nanowire single photon detector (SNSPD) is an optical detector with quantum-limit sensitivity. The detection mechanism is based on the Cooper-pair breaking by the photon energy, which results in a phase transition from superconducting state to non-superconducting state. SNSPDs surpass the semiconducting counterparts with high detection efficiency, low dark count rate, small timing jitter, short dead time, broad spectrum sensitivity as well as free-running etc. SNSPDs with high performance have been applied in various fields, such as, quantum information, laser communication, light detection and ranging. The progress of SNSPD research and development, application as well as commercialization at home and abroad in the past few years was summarized. An outlook of SNSPDs' RD as well as applications was also provided.
2018, 47(12): 1206001.
doi: 10.3788/IRLA201847.1206001
The laser and water-jet coupling technology is the key to realize water-jet guided laser machining. In order to improve the coupling accuracy, a new method was put forward based on off-axis optical system. The system was mainly composed of two convex lens, one for adjusting the axial position of laser beam waist, another lens for adjusting the radial position. The method can effectively improve the resolution of the coupling device. The theoretical analysis of the method was carried out, and an experimental apparatus was designed according to the analysis. The experimental results show that this method increases the radial resolution of coupling device by 5 times, which is consistent with the design. This method has been applied successfully to couple the laser into the nozzle of 100 m diameter, and it is also an innovative application of off-axis optical systems.
2018, 47(12): 1206002.
doi: 10.3788/IRLA201847.1206002
In order to investigate the effects of cryogenic laser peening(CLP) on the surface mechanical properties of 2024-T351 aluminum alloy, the Nd:YAG nanosecond pulsed laser was used to carry out the laser peening on 2024-T351 aluminum alloy at room temperature(25℃) and cryogenic temperature(-100℃), respectively. The micro-hardness, residual stress and microstructure of the samples were tested and analyzed, and the strengthening mechanism of CLP was discussed by the laser induced microstructure at room temperature and cryogenic temperature. The results show that, the dislocation density of CLP-treated samples is higher and the grain size on the surface is smaller than that of LPed after dynamic recrystallization due to the effect of cryogenic temperature on the sliding and annihilation of the dislocation. The surface micro-hardness and residual compressive stress of CLP-treated samples are respectively increased by about 20.3% and 21.6%, compared with LP samples, and the surface mechanical properties of 2024-T351 aluminum alloy are improved.
2018, 47(12): 1206003.
doi: 10.3788/IRLA201847.1206003
Laser cleaning technology, which is environment-friendly, has a wide range of application prospects in remanufacturing, micro-mechanical system (MEMS) and ultra-precision machining. Laser paint removing of aircraft surface is one of the important branches of the technology of laser cleaning. A high repetition frequency CO2 laser, with 10.6 m wavelength, was used to remove paint, which was double composite paint layer with thickness of 90 m, from aircraft surface (LY12 aluminum plate). It is shown that totally removed paint stripping and undamaged surface can be reached with selecting appropriate laser power density, scanning distance, and scanning time, the double composite paint layer on aircraft surface can be removed totally, the effect of paint removing on the tensile strength, yield strength, Vickers hardness and roughness of the substrate is studied by the method of experimental contrast. It is found that the mechanical properties of the aircraft surface did not change after the treatment of laser paint removing. Aircraft laser paint removing has more predominance than traditional methods, such as environmental protection without contact, high efficiency, parameters controlling, and low maintenance cost and so on, it develops new directions for applications in other fields.
2018, 47(12): 1206004.
doi: 10.3788/IRLA201847.1206004
The forward looking laser fuze could detect target range persistently, use range information to control the point-of-burst. The deviation of point-of-burst control is the key indicator that affecting the operational performance of air defense missile. Therefore, it is necessity to analyze the precision of point-of-burst control based on laser fuze. Under the assumption that guidance integrated fuzing(GIF) and uniform motion in the intersection stage, the global observability of point-of-burst was estimated based on sequential ranging. Then the Cramer-Rao lower bound(CRLB) of point-of-burst control precision was obtained when the ranging data met estimation errors of zero-mean additive Gauassian distribution. The system parameters such as miss-distance, initiation angle and spatial sampling rate which all influenced the control precision of point-of-burst were analyzed through numeric calculation. It provided reference for the design of high resolution laser ranging fuze.
2018, 47(12): 1206005.
doi: 10.3788/IRLA201847.1206005
In order to study the thermal load management mechanism of Yb3+:LuLiF4 crystal in anti-Stokes fluorescence process, laser cooling experiment based on standard pressure (1.0105 Pa) and high vacuum(2.510-3 Pa) states were carried out. The 5 mol% doped sample was supported by two optical fibers, and was placed in chamber with different vacuum states. The sample was excited via a 1 020 nm, 3 W laser. A temperature drop from room temperature of the sample was about △T12 K under standard pressure, and △T26 K under high vacuum. As for standard pressure state, thermal convection load of air was about 11.23 mW, thermal conduction load of the fibers was about 0.03 mW, thermal radiation load of the chamber was about 4.8 mW. As for high vacuum state, convection load of air was about 0.03 mW, conduction load of the fibers was about 0.07 mW, radiation load of the chamber was about 10.4 mW. As experimental results show, with the decrease of the pressure of the chamber from -105 Pa to -103 Pa, convection load of air is almost negligible, radiation load of the chamber becomes the most important thermal load of the refrigeration sample.
2018, 47(12): 1206006.
doi: 10.3788/IRLA201847.1206006
It is discovered that the jump point of the constant fraction discrimination(CFD) method moves forward when the laser receiver is saturated. In order to guarantee the range precision of laser fuze in short range, an error compensation algorithm based on the echo power equation was proposed for results correction. Firstly, based on a linear model to describe the pulse signal, the analytic expression of the saturation drift error was derived, and the relationship between drift error and echo signal slope was analyzed. Then, according to echo power equation, the compensation model of saturation drift error was established, in the case of the laser incidence on a specific target with a small angle. The error compensation expression was calibrated by experiment. Finally, a modified ranging formula was obtained. And the error compensation effect was tested by experiment. The results show that when the signal is saturated, the ranging deviates from the actual distance, and the deviation can be up to 1.4 m; due to the use of error compensation method, ranging deviation can be maintained between 0.5 m. Thus, this work can provide a theoretical reference for the design of miniaturized high precision laser proximity fuze.
2018, 47(12): 1206007.
doi: 10.3788/IRLA201847.1206007
The typical pulse from a TE CO2 laser consists of a 100 ns sharp spike followed by a long tail region spanning about 3-5 s. A simple pinhole plasma shutter was employed for eliminating the long tail part of the pulse due to strong laser absorption and scattering. Moreover, it remained the sharp spike of the pulse, thus the pulse width was modified. The shaped laser pulse waveforms at different pinhole positions were measured. The relationships between the laser pulse width, laser energy and defocus length were obtained, the pulse width of the CO2 laser from 110 ns to 50 ns was varied using the method. Further study indicates that the life of the pinhole plasma shutter is mainly determined by the laser pulse energy, repetition frequency, and shaped pulse width. It is shown that this plasma shutter will be used as a tool for short CO2 laser pulse shaping in the search for EUV source and lidar development.
2018, 47(12): 1206008.
doi: 10.3788/IRLA201847.1206008
In laser bending forming,the warping deformation influences forming accuracy of laminated plate. Therefore, the research of warping deformation in laser reciprocating scanning process has practical significance. Based on ANSYS software, a finite element model (FEM) was built. By simulating temperature field, stress field distribution and the free end deformation of the laminated plate, the mechanisms of warping deformation in single-pass reciprocating scanning process were analyzed. The results show that with the increase of reciprocating scanning number, a large variation of temperature makes heat energy equally distribute at both ends of scanning line, and thermal stress increases due to the cumulative effect of heat in the middle area. After each laser scanning, the residual stress on the bottom surface has an accelerating effect on warping deformation of the next scanning in laser action zone, which makes chordal height increase from 0.217 mm to 0.363 mm after scanning one to six times. However, as scanning number increases, the reduction in the promotion effect slightly decreases the growth of chordal height, and its maximum value is 0.058 mm. The max error of temperature field between the experiment and simulation is 9.85%, the max error of Z-direction displacement on warping line is 4.33% and the error of chordal height is 2.16%, which lays a solid foundation of calculation for better bending quality of the laminated plate.
2018, 47(12): 1206009.
doi: 10.3788/IRLA201847.1206009
It is hard to fabricate parts of Micro/Nano-Electro-Mechanical Systems (MEMS/NEMS). To solve this problem, the method of two-photon photopolymerization of femtosecond laser which had subdiffraction-limited spatial resolution was researched. Micro/nano fabrication system of Ti-sapphire femtosecond laser was set up. Process experiments of femtosecond laser two-photon photopolymerization were carried out using the material of liquid polymer. The experimental results indicate that the size of single solidification point reduces and the fabrication resolution improves with the reduction of laser power. The surface roughness value of the fabricated parts decreases, and the fabrication efficiency reduces with the scanning step reducing. 3D micro/nano structures composed of micro walls and nano wires was designed with CAD software and fabricated with two-photon photopolymerization of femtosecond laser. Nano wire whose diameter was smaller than 100 nm was fabricated after optimizing the process parameters. It is verified that two-photon photopolymerization of femtosecond laser provides an efficient method for micro/nano device.
2018, 47(12): 1206010.
doi: 10.3788/IRLA201847.1206010
The laser imaging radar based on Geiger APD array detection has the advantages of high sensitivity, high frame frequency, wide field, solid, small volume, and has become the development trend of laser imaging radar. At present, the APD array has fewer pixels and fewer device arrays, which can not meet the requirements of high resolution laser imaging. In order to solve this problem, one-to-one correspondence between laser dot array and APD array pixels was proposed. The imaging resolution was improved by splicing technique, and the laser imaging field was improved by micro scanning technique. By building an experimental system, the outdoor experiment was finished which had good imaging effects. The existing APD detector(3232) was used to improve the system spatial resolution by four times(6464), and the ability of laser 3D imaging was also improved.
2018, 47(12): 1206011.
doi: 10.3788/IRLA201847.1206011
Laser induced breakdown spectroscopy (LIBS) was employed to investigate the soil. LIBS analyses were performed with Nd:YAG laser operating at 1 064 nm, 5.82 ns pulse duration. The spectral lines of Ca Ⅱ 393.37 nm and Ca Ⅱ 396.85 nm were selected as the analytical lines for optimizing the experimental parameters (ICCD delay, laser energy, ICCD gate width, repetition rate and cumulative number of spectrum) which had influence on spectral line. The experimental conditions were determined as follows. The ICCD delay was 1 s, the laser energy was 50 mJ, the ICCD gate width was 3.5 s, the repetition rate was 1 Hz and the cumulative number of spectrum was 100 times. Under the optimal experimental conditions, the results of the electron temperatures Te and electron densities Ne were 11 604 K and 5.1551016 cm-3, respectively. The local thermal equilibrium condition of the plasma was satisfied. The results are useful for the analysis and detection of elements in soil.
2018, 47(12): 1230001.
doi: 10.3788/IRLA201847.1230001
With high accuracy, high spatial-temporal resolution, large scale coverage, coherent Doppler lidar has been widely applied in the detection of wind shear, aircraft vortex, wind power generation, atmosphere turbulence and so on. For lidar signal processing, the key issue is how to extract weak Doppler frequency shift in the weak backscatter signal. Based on the atmospheric slices model, the simulated echo signal of coherent Doppler lidar was processed by different time-frequency methods. Simulation results show that the adaptive optimal-kernel time frequency representation outperforms the others, having the advantages of lower computation cost, suppressing cross terms efficiently and higher resolution in both time and frequency domains. Then the adaptive optimal-kernel time frequency representation was applied to the field experiment data derived from a 1.5m Coherent Doppler lidar in Hefei, Anhui Province in March, 2017. The retrieved wind velocity results were compared with that derived from the fast Fourier transform algorithm. Experimental results show that the range resolution is 1.2 meter within 3 kilometers, and maintains the continuity of wind speed retrieved form weak signal using a 50-points window in the far field over 3 kilometers. Furthermore it can track the wind details better and enhance the detection range to 6 kilometers as the temporal resolution is set to 1 second.
2018, 47(12): 1230002.
doi: 10.3788/IRLA201847.1230002
Based on the CALIPSO satellite observations from June 2006 to December 2016, the aerosol spatiotemporal distribution characteristics above the East China Seas (the Bohai Sea, the Yellow Sea and the East China Sea) were analyzed. The results indicate that:(1) Aerosols in the three seas are mainly Clean Marine, Dust and Polluted Dust, and the sum of the three percentages is nearly 90%. The predominant aerosol type is different in different seas; (2) Aerosols above each sea tend to exponentially decay as the height increases. The aerosol type changes significantly in the space below 4 km, but there exists only Dust, Polluted Dust and Smoke above 4 km; (3) Temporal distribution characteristics show that almost all aerosol types vary with months and seasons. In spring, the three seas are Dust aerosols accounted for the largest proportion. In summer, Clean Marine aerosols obviously have the greatest impact for the East China Sea. In autumn and winter, the Bohai Sea and the Yellow Sea are mainly composed of Dust aerosol, while the East China Sea is Clean Marine aerosol as main component.
2018, 47(12): 1230003.
doi: 10.3788/IRLA201847.1230003
Using a tunable fiber laser of 1 550 nm wavelength, a high resolution imaging differential synthetic aperture ladar(DSAL) was set up in the laboratory. DSAL imaging experiments were carried out using a cooperative target at distance of 1.85 m. The phase history data (PHD) of the target returns were reconstructed and high resolution synthetic aperture images were generated by straightforwardly following standard DSAL image formation theory. High resolution DSAL images at various azimuth moving conditions were given in detail. Experimental data show that using the reconstructed PHD by DSAL technique, much better focused images can be produced, which demonstrates that the DSAL technique can robustly remove the common phase errors in the PHD. Moreover, DSAL images with various azimuth moving conditions show that even if the azimuth speed is 30% longer or shorter than its ideal value, the DSAL images are all well or at least acceptably focused, which means that a DSAL system is possibly well adaptive to the variation of its azimuth speed.
2018, 47(12): 1230004.
doi: 10.3788/IRLA201847.1230004
The calibration of water vapor mixing ratio is an important issue for Raman lidar. A dual wavelength lidar was developed and tested for the self-calibration of water vapor mixing ratio based on the two YAG laser, which emitted laser pulses at the wavelengths of 532.1 nm and 659.7 nm. From the analysis of the lidar measurements, it indicates that the capability of lidar satisfies with the requirements of water vapor mixing ratio self-calibration completely. In the altitude range, in which the measured aerosol liar scattering ratio was about 1.01, the calibration constant of nitrogen mixing ratio was determined to be 0.5450.031 from the lidar measurements, and the relative uncertainty was about 5.7%. The determination of the nitrogen mixing ratio calibration constant was the key step in the water vapor mixing ratio self-calibration, which lays a foundation for the self-calibration could and the water vapor mixing ratio.
2018, 47(12): 1230005.
doi: 10.3788/IRLA201847.1230005
A new sidelobe-suppression algorithm was proposed for the synthetic aperture ladar(SAL) with high sidelobe data. The theory of compressed sensing (CS) indicates that the sidelobe of the sparse signal can be lowered while reconstructing the signal, but the image signal of SAL is not sparse. Therefore, a sidelobe suppressing algorithm based on the modified spatial variant apodization (SVA) and SAL image reconstructed by the CS was proposed to deal with the high-sidelobe problem in real-time data imaging. SAL image signal would be converted to be sparse by the modified SVA first and the sparse signal would be reconstructed by the CS. The sidelobe of the SAL simulation data and the real high-sidelobe SAL image data were all suppressed respectively. The simulation result shows that in the premise of no broadening mainlobe, the sidelobe of the SAL image signal can be effectively suppressed by this algorithm.
2018, 47(12): 1230006.
doi: 10.3788/IRLA201847.1230006
The power spectral density(PSD) of the wind velocity disturbance was calculated by processing the measured echo signals by using Gaussian fitting estimation algorithm and maximum likelihood (ML)discrete spectral peak(DSP) estimation algorithm respectively. According to Kolmogorov turbulence theory, PSD has the relationship of -5/3 slope of frequency. It could be compared by different PSD under different distance gates. Wind velocity error in the high frequency region was used as the parameter of wind velocity estimation for comparing performance, and the error under different distances was analyzed and compared. The correlation of the relationship between wind velocity and time series was analyzed by using the autocorrelation coefficient. The results show that the wind velocity error of Gaussian fitting estimation algorithm is less than that of the corresponding ML DSP estimation algorithm in the low detection area, and the difference between the two wind speed errors does not exceed 0.05 m/s. In the area with higher distance, the difference of wind velocity error between the two algorithms increases from 0.06 m/s at 820 m to 0.16 m/s at 1 200 m. In the time-dependent analysis of the wind velocity, the autocorrelation coefficient of Gaussian fitting estimation algorithm between wind velocity and time is significantly larger than that of the corresponding ML DSP estimation algorithm, which shows that the wind velocity data processed by Gaussian fitting estimation algorithm is more stable.
2018, 47(12): 1230007.
doi: 10.3788/IRLA201847.1230007
3 vibrational absorption band of water vapor lies in the 935 nm spectral region. Differential absorption lidar has much higher measurement sensitivity in this region. Unfortunately, this spectral region is already at the edge of the gain bandwidth of Ti:Sapphire lasers and outside gain bandwidth of Cr:Alexandrite laser. Spontaneous fluorescence radiation of tunable dye laser is higher, which makes their spectral purity declinable. So optical parametric frequency convertor can be used as the transmitter for water-vapor differential absorption lidar(DIAL). The dynamically-stable ring resonator contains dual 70.7 cut, walk-off-compensated KTP nonlinear crystals, which is pumped with an injection seeded, frequency-doubled 532 nm Nd:YAG laser with repetition frequency of 10 Hz pulse. The resonator length of OPO was actively locked by injecting the distributed feedback semiconductor lasers of 935 nm and using ramp-hold-fire technique. The average output power of the transmitter was 4.5 W, the pulse length was 6 ns, the conversion efficiency of light (532 nm) to light (935 nm) was more than 17%, and the short-range and long-range frequency stability of light frequency was 30 MHz(RMS). The beam quality M2 was about 7.8, and the spectral purity can reach 99.9%. It will be one of the candidate light sources for remote sensing of atmospheric water vapor profiles.
2018, 47(12): 1230008.
doi: 10.3788/IRLA201847.1230008
The future high spectral resolution lidar(HSRL) system employs a narrow spectral filter to separate the particulate(cloud/aerosol) and molecular scattering components in the lidar return signals, which improves the quality of the retrieved cloud/aerosol optical properties. A simulation method of HSRL return signal based on HSRL detection principle was presented. The principle was that the CALIPSO cloud/aerosol extinction coefficient product and numerical weather forecast data were used to simulate the spaceborne HSRL 532 nm return signal. The performance of two typical spectral filters, i.e., Fabry-Prot interferometric(FPI) and iodine absorption filters, were analyzed using the simulated spaceborne HSRL return signals when they used as spaceborne HSRL molecular channel filter. The sensitivity analysis of three typical HSRL echo profiles(clear sky, cirrus cloud, aerosol, two-layer thick cloud) shows that the performance of iodine absorption filter was obviously better than that of FPI filter. The iodine absorption filter can maintain negligible relative deviation (4.010-3%), which was caused by the backward scattering effect of particles with low optical thickness(1.0). However, an FPI filter would still be a good choice for spaceborne HSRL systems if its particulate backscattering transmittance can be maintained below a level of 10-3.
2018, 47(12): 1230009.
doi: 10.3788/IRLA201847.1230009
Aerosol plays an important role in atmospheric optics, atmospheric radiation, atmospheric chemistry, atmospheric pollution and cloud microphysics, which has been an important factor of atmospheric monitoring. To better study temporal and spatial variation of optical characteristics of atmospheric aerosol, a scanning aerosol lidar employing a pulsed laser with single laser energy of 60 J at 532 nm was developed by Institute of Oceanographic Instrumentation, Qilu University of Technology,Shandong Academy of Sciences. The structure, technical parameters, detection principle and modes were introduced; some experiments were performed and analyzed. Through the measurements in Wheat Island marine environment monitoring station, the horizontal visibility under different weather conditions was analyzed. It was proved that the developed lidar can provide detection modes of time height indication(THI), range height indication(RHI) and plane position indication(PPI). The temporal and spatial variation of aerosol and cloud properties were analyzed through the data of different detection modes and extinction coefficient of aerosol in different moments retrieved by the Fernald method. The observational results show that the lidar can effectively acquire horizontal visibility, the distribution of aerosol in different directions, the temporal and spatial variation of aerosol, cloud and the structure of boundary layer.
2018, 47(12): 1204001.
doi: 10.3788/IRLA201847.1204001
The drawbacks of traditional temporal high pass filter were ghost artifacts and fixed pattern noise can't be removed completely. A non-uniformity correction algorithm that combines weighted guided filter and improved temporal high pass filter was proposed. Firstly, weighted guided filter was used to separate spatial high frequent components from infrared images accurately. Then, the change amplitude of every pixel value was calculated. Finally, different time constants were applied to motion regions and static regions to conduct non-uniformity correction. Two real infrared sequences were adopted in experiments, and space low-pass and temporal high-pass(SLTH) as well as bilateral filter based temporal high-pass filter(BFTH) were used to compare with the proposed algorithm. The experimental results show that the proposed algorithm is superior to the other two algorithms in subjective visual effect and objective evaluation inder. The proposed algorithm can reduce non-uniformity without causing ghost artifacts and achieves a better effect of non-uniformity correction.
2018, 47(12): 1204002.
doi: 10.3788/IRLA201847.1204002
Aerodynamically heated high temperature dome will produce strong infrared radiation. In some serious cases when the probe reaches saturation, the detecting precision of the seeker for target can be severely affected. In order to reduce the aerodynamic thermal radiation of the dome, a mathematical model of aerodynamic thermal radiation was developed. The aerodynamic heat and the aerodynamic thermal radiation of the hemispherical dome with different thickness were simulated numerically by software of finite element analysis and the mathematical model of aerodynamic thermal radiation. The influence of the thickness of hemispherical dome on the aerodynamic thermal response and aerodynamic heat radiation was analyzed and obtained. Research indicates that in the same flight conditions and in 10 s, when the thickness of hemispherical dome increases from 3 mm to 8 mm, the stagnation point temperature of the dome reduces by 16.41%; the thermal deformation of the dome reduces by 54.2%; the maximum irradiance of receiving surface of the detector decreases by 84.43%. Therefore increasing the thickness of the dome can not only reduce the temperature of the dome, but also effectively reduce the thermal deformation of the dome and the interference radiation illumination received on the detector.
2018, 47(12): 1204003.
doi: 10.3788/IRLA201847.1204003
Infrared radiance characteristic of cirrus atmosphere is the main clutter sources for advanced space-based electro-optical detecting systems. Based on bulk scattering parameters of cirrus particles in 2.7 m and 4.3 m wavebands, cirrus atmosphere radiance transfer model was constructed. With cirrus and atmosphere parameters measured by MODIS, the infrared radiation images of cirrus atmosphere were calculated. The statistical results of all pixels show that, in the 2.7 m band, the average radiance is 1.832e-23.024e-2 W/(m2sr), and the average radiance of cirrus pixels is 433 times larger than that of the clear-sky pixels; For 4.3 m in-band radiance of all pixels, the average value is 3.027e-22.99e-3 W/(m2sr), the maximum value is 2.37 times as large as the minimum.
2018, 47(12): 1204004.
doi: 10.3788/IRLA201847.1204004
Smokescreen is effective to counter infrared reconnoiter and guide. In order to assess and evaluate the ability of smokescreen to interfere IR imaging quantificationally, study was carried out both in theory and in experiment. Firstly, based on discrimination distance rule, the equation to calculate the view range of IR imaging under the interference of smokescreen was built from the aspect of radiation contrast, which made the analysis and evaluation of interference effect of smokescreen available from assessing the variation of view range of IR imaging before and after the interference. Secondly, transmissivity of smokescreen to different wavebands was measured in experiment. And then human body was selected as the target to observe. Normalized mutual information was selected as criterion based on correlativity rule and direct observation was used to analyze the interference effect of smokescreen on IR imaging in experiment. The results show that under the action of smokescreen, the apparent contrast between the target and background has dropped to less than 4% of their inherent contrast when the IR imaging system can't satisfy the demand of recognition. The corresponding transmissivity of smokescreen was 55%, and the theoretical calculation was consistent with the experimental analysis.
2018, 47(12): 1204005.
doi: 10.3788/IRLA201847.1204005
The short pulse signal amplification of a microchannel plate was studied by the transmission line method. The distortion of a single pulse signal and the change of the gain of the channel were discussed in detail. When the signal saturation parameter was more than 1, charges extracted by the pulse front edge can decrease the gain of the pulse trailing edge, resulting in the decrease in the gain of the pulse back edge. In addition, the mutual interference between multiple pulses was analyzed. If the next pulse arrived before the electron charge extracted by the previous pulse was fully replenished, the amplification of the latter pulse would also be affected. The effect of signal frequency on the gain of a microchannel plate was studied. When the total charges of a single pulse were constant, increasing the signal frequency could decrease the gain of microchannel plate. And the effect of signal frequency on the gain of the microchannel was not significant for signals with a same average current. The correctness of the above analysis was verified by the irradiation experiment of pulse laser on the image intensifier.
2018, 47(12): 1217001.
doi: 10.3788/IRLA201847.1217001
Based on digital micro-mirror device(DMD), a novel method for measuring high power laser far-field focal spot with high dynamic range was proposed. The region of focal spot was divided into two segments with different intensity range through DMD, and then captured by two CCD respectively. Image fusion technique was used to put two results together and the intensity distribution of high dynamic range focal spot was acquired. Based on the digital control of DMD, focal spot with different forms can be measured efficiently. The principle of focal spot division using DMD and the approach to obtain DMD control signal template were analyzed and the procedures of image calibration and registration for focal spot reconstruction were explained. The feasibility of the new method was verified by experiment. The results show that a dynamic range of 3 000:1 is achieved through the proposed method.
2018, 47(12): 1217002.
doi: 10.3788/IRLA201847.1217002
Combining laser heterodyne with linear frequency modulated technology, based on the measurement method of magnetostrictive coefficient, a novel method of linear frequency modulated multi-beam laser heterodyne measurement for magnetostrictive coefficient was proposed, which converted the measurement of magnetostrictive coefficient into the length variation. Based on linear frequency modulated technology, the information of length variation was loaded into the frequency difference of the multi-beam laser heterodyne signal, and many value of length variation could be acquired simultaneously after the multi-beam laser heterodyne signal was demodulated. Processing these values by weighted-average, length variation could be obtained accurately, and eventually the accuracy of magnetostrictive coefficient was improved. The magnetostrictive coefficient of the sample under different currents was simulated by Matlab. The results indicate that compared with traditional technique,the relative measurement error of this method is less than 0.09% and the accuracy is improved more than one order of magnitude.
2018, 47(12): 1217003.
doi: 10.3788/IRLA201847.1217003
Aiming at the design problem of the three-axis photoelectric tracking system for space target acquisition, firstly, the error source that affected the three-axis photoelectric tracking system to capture the space target was analyzed, and the main error was estimated, that was, track prediction error and three-axis pointing error. Then the error propagation relationship from the main error to the field of uncertain (FOU) was established, the uncertain area was calculated by using the transfer relation, and the search scanning mode was designed according to the size, shape and distribution type of the uncertain area. Taking an example of the shape of the field of uncertain as an ellipse and obeying the two-dimensional normal distribution, the design of the search mode was the branch spiral scan. Finally, the numerical simulation was also carried out to verify the correctness of the mode. By simulation calculation, the average acquisition time of the target was 10.52 s in the case of the capture probability of 98%. This mode provides a theoretical basis for the acquisition of space targets by three-axis photoelectric tracking system.
2018, 47(12): 1217004.
doi: 10.3788/IRLA201847.1217004
The scattering characteristics and the affecting factors of rough metal surface were analyzed based on the Kirchhoff approximation theory. Rough aluminum (Al) plates with different roughness were manufactured and their scattering characteristics were measured by two systems:a single-frequency system built with a far-infrared (IR) laser and a wide-band Fourier Transform IR spectroscopy (FTIR) system. Good consistency was found from the comparison of theoretical and experimental results. It is proved that the peak scattering coefficient has negative correlation with roughness and frequency, and positive correlation with incident angle. Additionally, the applicability of Kirchhoff approximation theory in the terahertz range was given by analyzing two limiting cases for near-smooth and high-roughness samples. The conclusions lie the foundation for theoretical calculation of complicated targets and will promote the development of the theories and techniques of terahertz radar.
2018, 47(12): 1217005.
doi: 10.3788/IRLA201847.1217005
In order to solve the problem that Kalman filter(KF) used in continuous, non-linear inertial navigation system(INS) suffered low accuracy in estimating model error, model predictive filter(MPF) directly processing continuous, non-linear system was adopted to provide one-step prediction for KF. Combining the advantages of the two filter algorithm, the accuracy of navigation could be further improved. Based on data tested by fiber-optic gyro(FOG) INS and star sensor(SS) data provided by computer, a simulation was executed for the presented combined filters, which proved the feasibility and superiority of the combined filtering algorithm in this paper.
2018, 47(12): 1217006.
doi: 10.3788/IRLA201847.1217006
In flight, the installation matrix of star tracker changed with the orbital period affected by the space thermal environment. In order to calibrate the variation of the installation matrices between star trackers caused by the structural distortion of the satellite, a real time on-orbit installation matrix calibration method based on quaternion adaptive Kalman filter was proposed. The algorithm was based on the combination of fading memory filter and simplified Sage_Husa adaptive filter. The algorithm adjusted the weight of the current measurement by adjusting the fading factor adaptively, which could restrain the filter divergence caused by the inaccurate model parameters. The results of simulation experiments and on-board data verification show that the q-AKF algorithm not only could restrain the divergence problem caused by the inaccurate model parameters, but also could track the real values of the installation matrix stably, when the attitude maneuver rates ranged from 0 to 5 ()/s. It is better in adaptability and robustness.
2018, 47(12): 1217007.
doi: 10.3788/IRLA201847.1217007
Natural birefringent elements such as wave plates and crystals are widely used in various optical systems. During the processing and coating process, residual stress will be introduced into the common optical components, causing birefringence. The birefringence has influences on performances of whole optical systems, which needs to be measured precisely. The birefringence measurement system was constructed based on the laser feedback effect, utilizing the linear relationship between light intensity modulation curve and birefringence in polarization flipping phenomenon. The long-term stable single longitudinal mode functioning of the laser could be fulfilled by utilizing frequency stabilization technique, which improved the anti-disturbance capability of the laser and the stability of the system. The experimental results show that the measurement accuracy of the system is within 0.24, and standard derivation of multi-measurement is within 0.18. The system can work on-line with good reliability and high stability. The system has potentials to be applied to on-line measurement of micro-stress, such as stresses in aircraft canopy, automotive glass, etc.
2018, 47(12): 1217008.
doi: 10.3788/IRLA201847.1217008
In order to reduce the measurement error because of the jolting of the vehicle, a novel two dimensional laser Doppler velocimeter (2-D LDV) was presented. And an idea of building an integrated navigation using 2-D LDV together with strapdown inertial navigation system (SINS) was proposed. The basic principle of 2-D LDV was expounded and the specific structure of the system using 2-D LDV together with SINS was discussed in detail. The result of theory and experiment show that the 2-D LDV reduces the measurement error because of the jolting of the vehicle, which has greatly improved the positional accuracy of the navigation system. The position error has been decreased from 936 m with pure SINS to 17.2 m with the 1-D LDV/SINS integrated system to 7.1 m with the 2-D LDV/SINS integrated system for the total distance of 29.67 km. 2-D LDV is more suitable for the vehicle integrated navigation system relative to the 1-D LDV.
2018, 47(12): 1218001.
doi: 10.3788/IRLA201847.1218001
With the increasing development of space technology, space optical system with the characteristics of high-performance, miniaturization has become a new hotspot research in space optical fields. Off-axis three-mirror optical system has the advantage of high quality image, large field of view and high level of lightweight etc., which can better suit the application of miniaturized and low-cost space optical system and has broad application prospects. Based on the Gaussian optics and three-mirror aberration theory, the off-axis three-mirror with freeform surface of tertiary mirror was designed. The focal length was 1 550 mm, field of view was 3.60.45, relative aperture was 1:6.2, degrees of freedom and image quality were increased efficiently by the introduction of freeform surface. The design results show that system has a better performance in effective field of view, modulation transfer function value is above 0.43@111 lp/mm, wave-front error maximum value is 0.049 (=632.8 nm), RMS wave-front error value is 0.034 , maximum grid distortion value is 0.9%, and the imaging quality is complete symmetrical about the tangential plane. The total length of the optical system is less than f'/3.1, the height is less than f'/4.1, and is easily implemented because of the relatively loose tolerance about processing and assembling. The obtained results have a certain reference value for miniaturized space optical system.
2018, 47(12): 1218002.
doi: 10.3788/IRLA201847.1218002
In order to meet the requirement of miniaturization, high image quality and large field of view of monitor lens, based on the monocentric structure lens and the development of curved sensor, a curved surface image monitoring lens optical system was designed. The FOV of the monitoring optical system is 140, the focal length is 7.88 mm, the F-number is 1.5, the total length is 15.12 mm, and the monitoring lens is up to 11-megapixel. The final design shows that the MTF value is closed to the diffraction limit in the central field of view and the 0.7 field of view, and is greater than 0.59 at the full field of view. The RMS radius of all fields of view are less than 0.6m. Compared with the existing monitoring lens optical system, this design achieves excellent image quality in a large field of view with a miniaturization structure.
2018, 47(12): 1218003.
doi: 10.3788/IRLA201847.1218003
A double wavelength combination and long focal length optical system was designed to combine and focus two direct high power laser diodes stacks with different wavelengths for laser material processing. First of all, the two LD stacks were collimated by fast and slow axis collimator respectively. Second, the two LD stacks were combined by double wavelength combine mirror. Then, the invert Kepler telescope system principle was applied to expand and collimate the laser beam in the slow axis direction. Finally, the fast and slow axis laser beams were focused at the same time. The focus optical system was analyzed by beam parameter product theory, and the focal depth was also be calculated by Rayleigh length formula. The whole optical path was simulated by ZEMAX software, and the simulation results were shown after ray tracing. Based on the theoretical analysis and ZEMAX simulation, the corresponding experiment were performed. After the combination and focusing, the focused spot size was 2.0 mm4.0 mm, and focal length was 300 mm. The final output power was 5 000 W and power density could reach to 104 W/cm2. The influence factors of this optical system were discussed finally. The focused spot can be applied to material processing, such as laser cladding and surface treatment.
Space remote sensing camera in the launch process and its in-orbit operation, due to environment change of atmospheric pressure, temperature, mechanics, results in focal plane defocus. In order to meet the requirements of imaging quality, the focal plane must be corrected before putting it into use. For meeting the features and imaging quality requirements of lightweight and miniaturization space camera, the focusing mechanism was designed, the motion displacement was in the range of 3 mm, and the weight was only 3.25 kg. The self-locking property of the worm drive mechanism was used to prevent the movement of focal plane in the external forces. Micro-precision linear rolling guideway was selected to ensure the linearity accuracy of CMOS target plane. At the same time, photoelectric encoder (16 bit) was used to real-time feedback the positioning information of target plane, forming a closed-loop control to ensure its positioning accuracy. And, the theoretical calculations, dynamic analysis and experimental verification, accuracy testing and analysis, calibration test of focal plane were worked out. Experimental results indicate that the first natural frequency of focusing mechanism is 182.7 Hz, it can effectively avoid the resonance phenomenon. And the linearity accuracy of CMOS target plane is better than 20, the positioning accuracy is better than 4.2 m, meeting the focusing accuracy. Simultaneously, calibration experiment of focal plane verifies the designed effectiveness of the focusing mechanism, meeting the imaging quality of space remote sensing camera.
2018, 47(12): 1218005.
doi: 10.3788/IRLA201847.1218005
With the increase of the aperture of the telescope, the inertia of the primary mirror increases sharply. Both of the temperature difference with optical surface and ambient air and turbulence fluctuation at thermal boundary layer result in heavy mirror seeing, directly influence the optical quality. A method based on computational fluid dynamics and optical path difference integrated calculation was proposed to evaluate the optical quality due to turbulence fluctuation at thermal boundary layer. To verify this method, the thermal boundary temperature distribution of a 3.0 m aperture primary mirror was simulated and calculated in different temperature warmer optical surface in natural and forced convection, respectively. Then, the temperature field was transformed to be refractive index field by corresponding equations. The optical performance of thermal boundary layer was calculated by optical path difference integration at the refractive index field. The results can quantitatively describe the effect on optical quality from the thermal boundary layer, which has made up for the deficiency of the existing seeing test. Meanwhile, it is verified that the existing astronomical observation requires the temperature difference between the primary mirror and the ambient air less than 2 K. The primary mirror thermal control system makes the optical path difference in forced convection decrease by an order of magnitude than that in the natural convection, which significantly improves the primary mirror seeing. Furthermore, it is indicated that the thermal control at optical surface is of great significant to improve the image quality.
2018, 47(12): 1218006.
doi: 10.3788/IRLA201847.1218006
The broad-area laser diode is widely used as a pump source in all-solid-state lasers,while the beam of semiconductor laser diode have to be shaped because of large divergence angle and the asymmetry of the narrow rectangular cross section in fast-axis and slow-axis directions. The output laser spot of area-broad diode laser with bright area:1 m(fast axis)200 m(slow axis) was rectangular and the mode characteristics of multiple filaments in the direction parallel to the p-n junction was analyzed. The far-field optical intensity distributions was simulated based on ZEMAX ray tracing software that operated in a non-sequential mode by setting appropriate filament size,spacing and multi-longitudinal mode. The simulation result was consistent with the real optical intensity distributions. Then a compact optical system of beam shaping was presented which consisted of a cylindrical lens and self-focused lens. The cylindrical lens was responsible for collimating the beam along its fast-axis, while the self-focused lens made the spot size become smaller. Finally, the image size was 0.15 mm0.17 mm and beam divergence angle was 3.32.4 in fast-axis and slow-axis directions, respectively, at 1.8 mm after self-focused lens. In the end, the comparison between the simulated intensity distribution and the experimental intensity distribution was performed step by step after placing optical element. It is shown that the method of simulating rectangular spots based on the broad area laser diode is feasible by introducing the filament structure.
2018, 47(12): 1218007.
doi: 10.3788/IRLA201847.1218007
An imaging spectrometer in the short infrared waveband of 1.0-2.5 m was obtained for the precision agriculture observation by air. The scientific performances parameters of the imaging spectrometer were analyzed for the requests of the precision agriculture. The perfect astigmatism corrected conditions were obtained based on the advanced Dyson imaging spectrometer. The enough axial and lateral spaces among each parts of the system guaranteed the arrangement of mechanisms of the slit, the detector and the optical elements. An imaging spectrometer with high optical performances as F number 1.5, the field of view 28, the slit length 25 mm, the spectral resolution 12.7 nm and the spatial resolution 1 mrad was designed. The aberrations were totally corrected and the tolerances of the system were loose. The research will be helpful for application of precision agriculture remote sensing.
2018, 47(12): 1220001.
doi: 10.3788/IRLA201847.1220001
Effects of heat transfer on grid lines of triple-junction solar cell irradiated by 1 070 nm CW laser were studied through the damage on triple-junction solar cell irradiated by laser with electroluminescence test. Three-dimensional model based on germanium solar cell was constructed with finite element analysis software COMSOL to simulate temperature distribution on triple-junction solar cell irradiated by CW laser. The results indicate that the top-cell of triple-junction solar cell is slightly damaged at the laser power density 72.5 W/cm2 and continuous irradiation time 41 s and the damaged region is firstly distributed along the grid line. The temperature of germanium solar cell in the simulation model has increased to 1 318 K and the grid lines which has high heat conduction rate result in the anisotropic heat transfer direction. The experimental results are well explained by the simulation model.
2018, 47(12): 1220002.
doi: 10.3788/IRLA201847.1220002
Currently, optoelectronic integration (OEI) has been new trend and hot topic in the fields of optoelectronics technology and information engineering. Especially, light source integration and technology compatibility have hindered the development and application of OEI. In this work, a simple structure of electrically-pumped excitonic laser diode was rationally designed and fabricated, which could be directly integrated on Si substrate. An Au/MgO/ZnO metal-insulator-semiconductor(MIS) heterojunction device was constructed based on the island-like polycrystalline ZnO film. Ascribed to the large natural lattice mismatch between Si wafer and ZnO epitaxy layer, the heteroepitaxy growth induced highly-disordered polycrystalline island-like nanostructure on the surface of ZnO film. Thence, the active region (nearby ZnO/MgO heterojunction interface) yielded a strong scatter media due to the spatial variation of refractive index. It greatly enhanced optical scattering and favored a low-threshold random lasing. The simple device structure design and fabrication technology provide a feasible way towards the bottom-up ZnO based optoelectronic integration.
2018, 47(12): 1220003.
doi: 10.3788/IRLA201847.1220003
In order to realize the integration of semiconductor laser diodes and detectors on a single chip, the research on the epitaxial material growth and structural process was carried out. A 1.3m InGaAsP/InP semiconductor laser diode chip with integrated monitoring photo diode (MPD) was fabricated by introducing an isolation region using an etching process. The photoelectric performance test of the chip shows that the laser diode has a low threshold current (17.62 mA) and high slope efficiency (0.13 mW/mA); the output power can reach 11 mW. In addition, under a reverse bias of -0.7 V, the detector region has a good linear response to the optical signal and the photocurrent of the MPD exceeds 0.3 mA, and the dark current can be as low as 25 nA with a reverse bias of -1.7 V.
2018, 47(12): 1222001.
doi: 10.3788/IRLA201847.1222001
Optical fiber communication technology has occupied the main position of the current communication transmission. But the single mode optical fiber (SMF) communication system based on wavelength-division-multiplexing (WDM) technology is now facing severe channel capacity crisis. Therefore, mode-division-multiplexing (MDM) technology based on the multimode or few mode fiber (FMF) has got the attention of many researchers. Mode Converter (MC) is one of the most important components in MDM technology, and long period fiber grating (LPFG) is a perfect all-fiber mode converter. The LPFG is used to convert LP01 mode to LP11 mode, and the multimode fiber is also used to eliminate inter-mode interference phonemenon in this mode converter. By using this mode converter, the converted mode has higher purity and better stability. The mode conversion efficiency reached 99.5% and there is no inter-mode interference phenomenon between these two modes. This MC device has good sensing characteristics, and this device has good linear sensitivity of strain, it can reach to 2.83 nm/N and 5.66 dB/N. So it can be concluded that this novel structure has excellent performance and will play an important role in the future application of optical fiber MDM and sensing field.
2018, 47(12): 1222002.
doi: 10.3788/IRLA201847.1222002
Based on the log-normal model in the turbulence channel, ultraviolet Non-Line-of-Sight (NLOS) diversity reception system was established. Using on-off keying(OOK) modulation, the bit error rate(BER) performances among three linear combining technologies as maximal ratio combining(MRC), equal gain combining(EGC) and selection combining(SC) for different scintillation indices and different receiving antennas were analyzed. The simulation results show that the BER performance of the three merge methods has been significantly improved compared with the case of no diversity. In the case of the same number of receiving antennas, the performance of the system by MRC is the best, followed by EGC, and SC is poor. The BER performance of different receiving antennas has been compared and analyzed, three linear combining technologies have strong ability to improve the performance with the increase of receiving antennas. In weak turbulence channel, the diversity reception technology can reduce the influence of fading and increase diversity gain.
2018, 47(12): 1222003.
doi: 10.3788/IRLA201847.1222003
The broad-band fiber-optic /4 waveplate is a special birefringent fiber with a slowly varying spin rate. When the spin rate gradually increases, it could transform the linearly polarized light into the circularly polarized light, covering a broad frequency range. Based on the loop model, the influence of the broad-band fiber-optic /4 waveplate on the scale factor stability of the all-fiber optic current sensor was analyzed. The eigen-modes of the fast-spun end and the coupling coefficient between the two orthogonal eigen-modes, along with the temperature characteristics, were measured using the trajectories on the Poincare sphere. Experimental results show that when the spin rate meets certain conditions, the influence of the broad-band fiber-optic /4 waveplate on the scale factor stability induced by the temperature variation is less than 0.2%, much weaker than that of the narrow-band fiber-optic /4 waveplate. The temperature stability of the all-fiber optic current sensor could be improved by using broad-band fiber-optic /4 waveplate.
2018, 47(12): 1243001.
doi: 10.3788/IRLA201847.1243001
The impulse coupling characteristics of space debris irradiated by pulsed laser with big spot was studied. The impulse coupling characteristics of planar debris under big and small spot irradiation were studied conservatively. The influence rules of shape and spot size under big spot irradiation on impulse coupling characteristics were studied. The rationality of theoretical research was verified by the experimental results. The results demonstrate that the impulse coupling coefficient with big spot radiation is higher than that of small spot radiation under the same laser power density. Impulse coupling coefficient under big spot irradiation is mainly affected by laser power density. The influence of spot size on impulse coupling coefficient is small. The theoretical calculation results of impulse coupling coefficient under big spot irradiation are closer to the experimental results. The above experimental results have certain guiding significance for the theoretical study of laser irradiated non-planar space debris.
2018, 47(12): 1243002.
doi: 10.3788/IRLA201847.1243002
The change of temperature in satellite have a direct influence on the performance of electrical devices. Aiming at studying the performance of electrical devices due to temperature distribution of radiant plate, the mechanism of temperature dissipation of the radiant plate was analyzed based on its characteristics. The research on thermal effect of laser irradiation in a simplified model of radiant plate was done by using the finite element analysis software. The transient temperature distribution under pulsed laser radiation was got by numerical simulation of the surface temperature field. The pulsed laser was used as the radiation source to irradiate the radiant plate, based on analysis and study of the simulation results, it was founded that the temperature of the electronic device would rise by 64.5 K when there was no heat dissipation around the electrical devices. When the heat pipe radiator was in the maximum working performance, the thermal effect of pulsed laser irradiation would seriously affect the heat dissipation performance of the heat pipe,the abnormal work of the heat pipe would increase the temperature of the electronic device and affected the normal operation of the electronic devices. It lays a theoretical foundation for the influence of the temperature on the performance of electronic devices.
2018, 47(12): 1243003.
doi: 10.3788/IRLA201847.1243003
In the high power laser system, surface impurities and nodule defects are the key factors causing laser-induced damage of thin film components. The influences and variations of surface impurities and nodule defects on the laser-induced damage of thin film components for different irradiation time and power density were analyzed by establishing the thermal analysis model of thin film components irradiated by continuous high power lasers. The results indicate that, when the surface impurities are irradiated by continuous high power lasers, and their size localizes within a certain range, the maximum temperature of the film components increases with the increasing of impurity size, and the large and shallow nodule defect seeds have a more obvious influence on the temperature rise of the film. With the increasing of the power density and the irradiation time, the range of the impurity size in which the surface impurities cause the thermal melting damage of the thin film components increases. Simultaneously, the range of the seed depth and size of the nodule defects causing the thermal melting damage of the thin film components is broaden.
2018, 47(12): 1207001.
doi: 10.3788/IRLA201847.1207001
In order to transform a Gaussian beam with uniform polarization into a vector beam with tunable polarization distribution, an optical method was proposed to generate vector beam and control the polarization distribution, based on the polarization characteristics of the S-wave plate and double retarders. Combined with the Stokes-Mueller matrix algorithm, a mathematical model of the polarization control of vector beam was established. And the polarization states distribution of the output beams were calculated, when a linear polarized Gaussian beam passed through the S-wave plate and the double retarders (including two situations:double quarter-wave plates and double half-wave plates). The relationship between the angle of the double retarders and the polarization distribution regular pattern of the output vector beam were discussed. The experimental results agree well with the numerical simulation results, which show that the method can achieve the complex polarization control for a scalar coherent beam, and the correctness of the theoretical analysis is verified.
2018, 47(12): 1207002.
doi: 10.3788/IRLA201847.1207002
A new type of composite vortex beam was generated by the coaxial superposition of two high-order radial Laguerre-Gaussian beams with the same radial indices and opposite topological charges. The intensity distribution characteristic and space propagating property of composite vortex beams were studied theoretically and experimentally. The results show that the composite vortex beam, which is superimposed by the high-order radial Laguerre-Gaussian beam, has a multi-layer bright petal; When the beam waist radius are same, with the increase of propagation distance, the intensity distribution of the beam spreads but does not rotate; When the waist radius are different, the intensity distribution rotates, and the phenomenon of rotating tail appears. The rotating direction and trailing direction depend on the number of topological charges and the size of the waist radius. The results provide an experimental basis for understanding the generation of composite vortex beam and further extending its application scope.
2018, 47(12): 1212001.
doi: 10.3788/IRLA201847.1212001
Complex oceanic environment(OE) is a typical scene in space photoelectric detection. Ocean surface albedo(OSA) from visible to far-infrared is of great importance to study of ocean atmospheric transfer and background radiative properties. However, the OSA in China Sea areas was less studied at present. This study built a fast parameterized OSA application model on the basis of statistical analysis of multiple-satellite measured long-time OE parameters. The new model took chlorophyll concentration of sea water, aerosol optical depth, ocean surface wind speed and solar illuminating angles into account. The fast parameterized application model of sea surface albedo was established, and the spectral curves of 0.4-14 micron sea surface albedo in the South China Sea, the East China Sea, the Yellow Sea and Bohai were obtained, and spatiotemporal features of OSAs were analyzed. These OSA spectrum provides fundamental data support for space photoelectric engineering applications above seas.
2018, 47(12): 1237001.
doi: 10.3788/IRLA201847.1237001
In order to improve the performance of perturbation rejection and the accuracy of tracking for the large telescope, the control system of the telescope needs to have a good dynamic performance, which is due to the closed-loop bandwidth. Firstly, the factors that affect the close-loop bandwith and the dynamics of the telescope control system were analyzed, which were based on the two-mass spring-mass model of the telescope structure, and then two methods including structural filter and acceleration feedback methods which could improve the closed-loop bandwith of the control system, were introduced. Secondly, the application of the structural filter and acceleration feedback methods in the telescope control system was analyzed in detail. Lastly, the related problems that the structural filter was used in the telescope control system were analyzed and the effectiveness of acceleration-feedback control for improving the closed-loop bandwidth was introduced. The experimental results demonstrate that compared with the structural filter method, the acceleration-feedback provides a better technology to improving the closed-loop bandwidth of control system for the large telescopes.
2018, 47(12): 1223001.
doi: 10.3788/IRLA201847.1223001
The algorithm was proposed based on the empirical mode decomposition and regression analysis to extract and identify the characteristic information of spatial heterodyne spectroscopy. The spectrum which was obtained by pre-processing the original probe data was decomposed into several intrinsic mode function components by empirical mode decomposition and the each order IMF's Pearson correlation coefficient was calculated with the original spectral signal. According to the correlation coefficient classification criteria, the demarcation point of the background and target information reconstruction will be determined. Then the Pearson correlation coefficient between the reconstructed background and the measured background was calculated to determine the empirical mode decomposition results. At the same time, the signal-dominated components were de-noised respectively by the wavelet soft threshold and then the pure target characteristic signal was reconstructed. By using multiple linear regression analysis to process the target characteristic information and the original interference spectral information, the optimal coefficients of time-domain filtering will be obtained. The filter will be constructed to extract the target. Finally, the signal of extracted target will be identified by Pearson correlation coefficients. The experimental results show that the background and the target can be separated by the empirical mode decomposition. In the case of unknown background signal, the empirical mode decomposition and regression analysis can be used to extract the characteristic spectrum of potassium resonance.
2018, 47(12): 1226001.
doi: 10.3788/IRLA201847.1226001
Aiming at the problem of low registration accuracy of traditional laser scan matching method under multi-obstacle environment, a matching method based on graph theory was proposed. In this method, concave and convex points were extracted from the data points, then the corresponding line segments were extracted and the attribute graph model was constructed. The point set registration problem was transformed into an attribute graph matching problem. The registration parameters were determined by comparing the observed graph model with the reference model. Compared with the traditional matching algorithm based on line segments, the proposed algorithm introduces more geometric attributes between line segments, which have better robustness in multi-obstacle environment or dynamic multi-obstacle environment. Compared with the traditional matching method based on points or feature points, the proposed algorithm constructs the attribute graph model based on the more specific feature points, say convex points and concave points. In this way, the proposed algorithm not only improves the operation efficiency, but also avoids the local minima problem in multi-obstacle environment and dynamic multi-obstacle environment.
2018, 47(12): 1226002.
doi: 10.3788/IRLA201847.1226002
In recent years, polarization correlated imaging has been widely studied by researchers. It has great practical value in the field of target detection and feature extraction. A full Stokes polarization correlated imaging system can obtain multiple polarized images of the target. Using these images, the intrinsic polarization information of the target can be analyzed from different views. However, there is a strong complementarity and redundancy between these images. Therefore, HSL-RGB image fusion technology was applied to this system. The number of polarized images acquired by the system was effectively merged to comprehensively describe the target structure and improve the target detection and recognition efficiency. The experimental results confirm that the fusion technique is effective in improving the recognition and detection performance of polarization correlated imaging system.
2018, 47(12): 1226003.
doi: 10.3788/IRLA201847.1226003
Cells use force as a mechanical signal to sense and respond to their microenvironment. To this end, PDMS micropost arrays has been widely used in cell traction force measurement, which allows calculating magnitude and direction of cell force from the deflection of the micropost. However, the inherent transparency of PDMS leads to the complexity of image processing algorithm when retrieving the top surfaces centroids of the deflected microposts. A method of modifying the top surfaces of PDMS microposts using magnetic beads was proposed to attain opaque top surface of the micropost, enabling a higher contrast between the top surface and the substrate of the micropost array. Magnetic beads were brought into the molds by applying a magnetic field and casted in the PDMS microposts during soft-lithography process. The modified micropost arrays with opaque top surfaces were imaged using an inverted microscope as disk-shaped patterns top surface. The centroids of disk-shaped patterns in the microscopic image were calculated using regionprops function, while Hough transform was required to process the ring-shaped patterns of the conventional transparent microposts made with pure PDMS. The experimental results show that the contrast between the top surface and the substrate is significantly improved, hence precluding the need of using Hough transform, reducing the algorithm complexity in image processing, and improving the precision of micropost positioning.
2018, 47(12): 1226004.
doi: 10.3788/IRLA201847.1226004
Aiming at the problem of tracking failure caused by object occlusion and out of view in object tracking, a two-step correlation filter for object tracking algorithm was proposed to advance the robustness of the object tracking via correlation filter. Firstly, according to the characteristics of different cell size of histogram of oriented gradient (HOG) feature, a two-step correlation filter object tracking framework was presented, which can improve the tracking accuracy and simultaneously ensure the tracking speed. Then, fusing multiple object features and obtaining more characteristic representation comprehensively were to promote the robustness of object tracking. Finally, an object template adaptive updating strategy was proposed based on the object tracking confidence index, which was to solve the problem that the object template was contaminated when the target was occluded. The experiment was validated on the OTB100 standard object tracking dataset. The results of comparison with other tracking algorithms show that the tracking accuracy is improved by 6.0% and the tracking success rate is increased by 5.5% in comparison with the optimal tracking algorithm, and the average tracking speed is 27.4 fps, which ensures the real-time performance of object tracking. In the application of actual object tracking, the algorithm can still track the target stably and accurately in the case of severe occlusion.
