2016 Vol. 45, No. 12
column
- Infrared technology and application
- Laser technology
- Teraherta technology and application
- Terahertz technology and application
- Atmospheric optics
- Photoelectric devices and microsystem
- Advanced optical material
- Advanced optical materials
- Micro-nano optics
- Biophotonics
- Structure and control
- Photoelectric navigation and control
- Photoelectric measurement
- Optical design and simulation
- Spectrum detection and analysis
2016, 45(12): 1204001.
doi: 10.3788/IRLA201645.1204001
Study of the sub-surface damage induced by chemical-mechanical polishing method has been carried out for HgCdTe material. The optical characterization was performed for the surface after repeated step removal by wet etching using spectroscopic ellipsometry. It was found that the depth of sub-surface damage layer was about 15-20 times of the diameter of the abrasive particles. Through the comparison of the minority carrier lifetime and performance of the ultimate photoconductive detectors, it was considered that an obvious improvement could be achieved by a complete removal of this sub-surface damage layer.
As to the complexity and low analysis efficiency of defect identification inverse problem solution by manual programming model, with the conjugate gradient algorithm, a method for the secondary development of the universal finite element numerical computation software Ansys was put forward in this paper, which is successfully applied to the diagnosis of the irregular inner-wall surface defect by infrared inspection. And a new concept of relative sensitivity was introduced here in order to assess the influence of inspection state to the quantitative identification of defect boundary shape. Through analyzing the relative sensitivity, it was found that the inspectability of the irregular inner-wall surface defect was different in the different inspection states, and the inspection carried out at the time with maximum inspection surface temperature difference was more desirable than that in the steady heat transfer state. Both of the feasibility of the infrared diagnosis with Ansys secondary development and the validity of the relative sensitivity assessment were verified by the numerical experiment.
2016, 45(12): 1204003.
doi: 10.3788/IRLA201645.1204003
A SNR-C model to quantitatively predict the leak gas detection capability of thermal imager was proposed. Using this model, methane gas concentration of cooled thermal imager GasFindIRTM at SNR=1 was predicted, which was consistent with the measured results. The indoor testing setup was designed and built, SNR-C curves of uncooled thermal imager Photon320 to detect ethylene were tested at different temperatures of blackbody, namely 298, 303, 308, 313 and 318 K. Through analysis, measurement and prediction concentration at SNR5 were relatively close in all of five blackbody temperatures, and respectively prediction concentration are 3146, 987, 570, 394 and 298 ppm. And this variation trend was consistent with the measured concentration. Therefore, the SNR-C model put forward in this article was able to predict the gas detection capability of thermal imager. While the testing setup can quantitatively measure the relationship between SNR and gas concentration, which can be applied to test the indoor performance of gas leak detection of thermal imager.
2016, 45(12): 1204004.
doi: 10.3788/IRLA201645.1204004
The calibration data are meaningful in measurement of infrared radiometric characteristics for target and its background. They also play an important role in IR imaging guiding simulation test application. The field radiometric calibration methods for infrared detecting system with fixed focal length are analyzed at first. Three kinds of methods were briefly introduced and compared, and the applicability of different methods was pointed out. In order to compare the characteristic change of three methods, short distance radiometric calibration, a certain distance radiometric calibration and radiometric calibration using of extended area blackbody and collimator were used in this research. And then the experiments by different radiometric calibration methods were investigated. The short distance radiometric calibration results show that it isn't suitable for infrared reconnaissance and warning detecting system. The certain distance radiometric calibration results show that it needs further calculation of environment radiation, path radiation and path transmission. Then, the environmental parameters is loaded in MODTRAN soft ware to predict environment radiation, path radiation and path transmission. But it's difficult to obtain very accurate calculating results. To measure the target radiation characteristics, radiometric calibration using of extended area blackbody and collimator is necessary. The research is useful for technical innovation of the out-field radiometric calibration of infrared detecting system. It also can be applied to system design of target characteristics measuring system.
2016, 45(12): 1204005.
doi: 10.3788/IRLA201645.1204005
Selecting a fine atmospheric site is very important for ground-based infrared astronomy. The sky background radiance and atmospheric transmittance are important factors for selecting site. Combined observations of solar spectral extinction and forward angular scattering were presented with ground-based FTIR on Yangbajing, Tibet. The direct solar irradiance and atmospheric background radiance were showed on 8-14 m band. According to the atmospheric parameters, the direct solar radiance, atmospheric spectral transmittance and background radiance of selecting sites were compared by CART on long-wave infrared band. These will be useful to select a site for ground-based infrared solar telescope.
2016, 45(12): 1205001.
doi: 10.3788/IRLA201645.1205001
By introducing the proton implantation(PI) process in the photonic crystal(PhC) vertical-cavity surface-emitting lasers(VCSEL) fabrication to confine the injection current in the devices can make the mesa process become pure plane technology. It reduced the fabrication difficult of the photonic crystal structure, simplified the fabrication processes, and improved the L-I-V characteristics uniformity of the devices. In the PI-PhC-VCSEL, the photonic crystal structure can control light beam and mode characteristics of the devices, when the current injection hole diameter is less than the center defect diameter of the photonic crystal. This effect in the PI-PhC-VCSEL can be used to optimize the threshold current and enhance the performance of the devices; it also can be used to realize high output power low threshold current single fundamental mode PI-PhC-VCSELs. A device with threshold current of 2.1 mA, output power larger than 1 mW, the divergence angle less than 7 was designed and produced. The device can operate with single fundamental mode with the injection current less than 12.5 mA and the effect of the photonic crystal in the PI-VCSEL has been demonstrated.
2016, 45(12): 1205002.
doi: 10.3788/IRLA201645.1205002
A ring cavity Tm-doped fiber laser system was built based on a 1 550 nm fiber laser. And, its spectral chacteristics were investigated. With 1 550 nm pump, the spontaneous emission of the 1.6 m long Tm-doped fiber covered a spectral range from 1 800-1900 nm with a 3 dB bandwidth bigger than 60 nm. Inserting an isolator into the ring cavity, narrow linewidth output was obtained with a 3 dB linewidth smaller than 0.2 nm centering at around 1 900 nm. Further adding a tunable FP filter, tunable, narrow linewidth laser output was attained. The laser spectrum was tunable from 1 840-1 900 nm with a broad tunable range reaching 60 nm while maintaining a 3 dB linewidth of only 0.07 nm. In addition, a telecommunication FP filter at the 1 550 nm waveband was also exploited in this ring cavity laser system for wavelength tuning. And, a narrow linewidth, broadband tunable laser output in two seperated spectral ranges was also recorded. Together with the 2 000 nm FP laser system, this laser demonstrates a wide tunable range from 1 820-1 915 nm which is consistent with the spontaneous emission spectrum of the Tm-doped fiber.
2016, 45(12): 1205003.
doi: 10.3788/IRLA201645.1205003
In order to realize the high repetition rate operation in Q-switching with good beam quality. A diode-pumped acousto-optic(AO) Q-switched master oscillator power amplifier (MOPA) all-solid-state laser with high repetition rate and high power was demonstrated by using a master oscillator power amplifier with two-pass amplification configuration. The structure and relevant parameters of the master oscillator power amplifier(MOPA) were optimized, the research of the high power MOPA system was completed. Through arranging the optical components in the resonator reasonably to improve beam quality, the focusing lens and aperture were used to achieve the laser mode matching. The maximum average power of the MOPA system is 51.3 W. Short pulses of 18.62 ns with beam quality MX2=1.882、MY2=1.971 at 50 kHz. And the corresponding total optical-to-optical efficiency is 23.75%. With the help of gain guiding effect, the quality of the beam which emitted from master oscillator power amplifier(MOPA) laser system can be improved.
2016, 45(12): 1205004.
doi: 10.3788/IRLA201645.1205004
As the working temperature can affect emitting wavelength of distributed feedback(DFB) laser and reduce measurement sensitivity of magnetic field of Spin-Exchange-Relaxation-Free(SERF) atomic magnetometer, a DFB lasers' temperature controller with high-precision and high stability was designed and developed by using digital proportional-integral-differential(PID) control technology, which is based on TMS320LF2812 core controller. In terms of hardware design, the temperature controller consists of temperature control forward pathway and temperature acquisition backward pathway to form a complete closed-loop temperature control structure. In consideration of software design, the three parameters P, I and D are determined by using Ziegler-Nichols engineering setting method. Using the aforementioned temperature controller, a temperature controlling test was performed on a DFB laser with a center wavelength at 852 nm. Experimental results indicate that, the control scale is 5-60℃, the accuracy is 0.02℃, and the control procedure is 20 s. Meanwhile, the stability of working temperature is better than 7.910-4(RMS) during long term(220 min) running, which provides performance guarantee for SERF atomic magnetometer in practical application.
2016, 45(12): 1206001.
doi: 10.3788/IRLA201645.1206001
A dilation framing camera based on the gated microchannel plate (MCP) technology and the time-dilation technology was reported. In the camera, the photo-cathode (PC) was applied with a high voltage fast step pulse with gradient of 2.1 V/ps. The electron pulse generated at the PC was accelerated by a time varying electric field between the PC and the anode mesh, which leads to an energy dispersion of the electron signal. The electrons generated early in time obtain a larger energy. Therefore, the initial electrons transit the drift space between the mesh and the MCP at a higher velocity than those coming later. While the electrons travel through the 50 cm drift space to the MCP, the temporal shape of the electron signal was dilated or temporally magnified due to the time-dilation system. Then, the dilated electron pulse was detected by the gated MCP framing camera. Therefore, the temporal resolution of the framing camera was improved. The camera has three transmission photo-cathodes coated with 80 nm Au. The width of each PC is 8 mm. Both the PC and the MCP were applied with pulse, therefore the laser pulse, the PC pulse, and the MCP pulse should be synchronized accurately. The synchronized process was analyzed. While the PC was applied with dc bias only, the measured temporal resolution of the camera without time-dilation was about 78 ps. While the high voltage fast step pulse was applied on the PC, the temporal resolution was improved to 12 ps. The relationship between the temporal resolution and the synchronized point was also provided.
2016, 45(12): 1206002.
doi: 10.3788/IRLA201645.1206002
In order to study the melting characteristics of polymethylmethacrylate(PMMA) by CO2 laser irradiation, according to the heat conduction and energy conservation principle,the theoretical model of PMMA melting was established by low-power CO2 laser radiation. The laser parameters threshold of PMMA melting was calculated and the relationship between sample temperature change and laser parameters was analyzed. By the use of digital microscopy systems, SEM and XRD instruments, the melt morphology and tissue features of PMMA sample were discussed. The results show that laser power density 31.8 to 47.7 W/cm2 could make PMMA melt and does not occur thermal decomposition, and the experimental results is consistent with the theoretical calculations of laser melting threshold, which provides reference for CO2 laser melting mechanism and molding technology of PMMA.
2016, 45(12): 1206003.
doi: 10.3788/IRLA201645.1206003
The laser molten pool width detection technology of the closed-loop control system in metal parts laser forming process was researched. A method of applying Kalman filtering for molten pool width detection in laser forming process was presented. The vision sensing system collected the images of the molten pool in laser forming process. The molten pool width calculated by image processing was used as a parameter to establish a state equation and a measurement equation. A Kalman filter recursively computed the solution over least squares approaches to equations which were established based on an estimation of the width and the displacement in width. The Kalman filter optimized the estimation of the molten pool width at the next sampling time and reduced the measurement errors caused by the process and sensor noises. Experiment results show that measurement average errors decrease from 0.028 mm to 0.009 3 mm. Experiments demonstrate the effectiveness and great improvement of precision by using the proposed algorithm in the molten pool width detection.
2016, 45(12): 1206004.
doi: 10.3788/IRLA201645.1206004
The thermal management technique of multi-layer Cr4+:YAG medium was presented for mitigating the deleterious impact of thermal effects in a cryogenic helium gas cooled Yb:YAG multislab amplifier with Cr4+:YAG interlayers operating at a high repetition rate, by means of optimizing the architectures of Cr4+:YAG interlayers and claddings in the laser slabs. The distributions of temperature, stress, depolarization losses and optical path difference in four amplifier architectures with different Cr4+:YAG parameters were numerically calculated by a three-dimensional finite element analysis and the Jones matrices method. Based on these results of the propsed modelling, it was showed that the properly designed two-layer and three-layer Cr4+:YAG could decrease the heat deposition of the Cr4+:YAG around the gain media, and hence result in a very small transverse temperature gradient (1.5 K) in the first slab. When the laser beam traveled through the whole amplifier, the average thermal-stress induced depolarization losses and optical path difference for the laser amplifier head were reduced to 0.5% and 0.8, respectively. Furthermore, the negative impact of thermal effects on the output beam quality can be vanished by properly designing the number, widths, and absorption coefficients of the multi-layer Cr4+:YAG medium, which are beneficial for the engineering/design of the next generation of high energy, high power lasers.
2016, 45(12): 1206005.
doi: 10.3788/IRLA201645.1206005
Five coherent hole-burning can be simultaneously observed in the absorption spectra of four-level N-style atoms vapors. In this system they adopt a saturated laser co-propagates and two coupling lasers counter-propagate with a probe laser, and the saturated laser can not be in the destructive Doppler state with the probe light. The positions of the coherent hole-burning can be explained by Dressed-state theory. The middle narrow deep hole-burning is induced by the superposition of two coherent hole-burnings. The depth of the coherent hole-burning can be changed by adjusting the reference parameters and the Rabi frequency of the saturated laser. The positions of the coherent hole-burning can be changed by modulating the Rabi frequency of the probe light. By numerical simulation it is found that Rabi frequency of the saturated light plays an important role in slowing the propagating speed. These results may be useful in optical quantum memory and optical quantum information.
2016, 45(12): 1206006.
doi: 10.3788/IRLA201645.1206006
In the last ten years, the laser active imaging technology on Geiger-mode focal plane APD has becoming the research hotspot on the international, because of its advantages on the detection sensitive, spatial resolution, and range resolution. Considering the characteristic of atmospheric transmission, the InGaAs or HgCdTe APD arrays has been selected firstly. Based on the InGaAs 3232 APD arrays by domestic developing, the experimental platform of 1 570 nm laser active imaging was established. The target images from 3.9 km were captured on the condition of the frame 1 kHz, pulse energy 2 mJ, and the clear target surface structure range images from 720 m were collected. Through this field experiment, it is proved that the performance of Gm-APD arrays is good, and the platform can demonstrate the function of laser active imaging in the field. The experiments state that 1 570 nm focal plane APD laser radar can provide the well imaging performance, and it can remote sensing detection of the far distance target, laying the good research foundation for the future practical applications.
2016, 45(12): 1206007.
doi: 10.3788/IRLA201645.1206007
Detecting silicon damage evolution induced by laser irradiation on the focal plane was researched through the change of cat's eye echo. With the time increase of laser irradiation, the echo images started to shake and new texture appeared, which indicate the silicon was damaged. The area of echo images corresponding to the silicon damage expanded unceasingly. The facular structure in the damaged echo image became complicated and the facular area became smaller. The damaged echo image was dynamic stability under the laser irradiation at last. According to the change of echo images, the silicon damage morphology were analyzed. The phenomena of surface oxidation, small scale damage and the expanding of damaged area were observed. The corresponding relationship between the echo image texture feature and the silicon damage morphology was analyzed preliminarly. The correlation and angular second moment would be decreased if the roughness of the damage morphology increased.
2016, 45(12): 1206008.
doi: 10.3788/IRLA201645.1206008
The advantage and disadvantage of different scannerless three-dimensional laser imaging systems was compared, the intensity modulation scannerless three-dimensional laser imaging technology based on multi-channel receiver was proposed. The technology has the advantage of fast imaging, high precision, high reliability, long distance. The high power pulse laser as the illumination source, two ICCD received the echo from dual channel sub optical system at the same time, the distance information was analyzed through the ICCD intensity information. The technology principle and approach was introduced. The principle sample machine was designed, and on which the imaging experiment was carried out. The experiment result shows that the imaging range is 5.1 km, range resolution is 0.25 m when range is 30 m.
2016, 45(12): 1206009.
doi: 10.3788/IRLA201645.1206009
It has very important application value to investigate the damage performance of K9 glass irradiated by ultraviolet excimer laser. In this paper, the experiment research on damage in K9 glass irradiated by 248 nm KrF excimer laser was carried out, the sample damage threshold and damage morphology were analyzed by means of metallurgical microscope and scanning electron microscope. The comparison of laser induced damage performance between KrF excimer laser and pulse CO2 laser were investigated. The experimental results indicate that the damage mechanism of K9 glass irradiated by KrF excimer laser and pulse CO2 laser mainly follow the thermal-mechanical coupling mechanism. However, there is apparent difference in damage threshold and damage time. For example, the damage threshold is lower and the damage time is shorter for KrF excimer laser. This can be explained by the difference in wavelength and photon energy between the KrF excimer laser and pulse CO2 laser. The research presented in this paper is helpful for further exploring the ultraviolet excimer laser damage mechanism of optical materials.
2016, 45(12): 1206010.
doi: 10.3788/IRLA201645.1206010
In inertial confinement fusion laser driver, ultraviolet laser damage of fused silica lens is an important limiting factor for lifting load capability of the laser driver. Considering the above reason, a new configuration of frequency tripling is proposed to solve this problem. The frequency tripling crystal is placed on the back of the focusing lens, thus the sum frequency generation of the fundamental frequency light and doubling frequency light occurs in the beam convergence path. Incident angle of the convergent beam is up to 36.35 mrad, thus the frequency tripling crystal must have a large acceptance angle for phase matching condition. LBO crystal which also has high damage threshold is employed as the frequency tripling crystal. Theoretical analysis indicates that three tiled LBO crystals with different cutting angles will meet the requirement of phase matching and principle experiments also supported this scheme. By employing this configuration, the fused silica lens will only be irradiated by fundamental frequency light and doubling frequency light and its damage threshold will be improved, thus the load capability of the laser driver will be lifted. At the same time, the limitation of growth size with LBO crystal will be broke through.
2016, 45(12): 1206011.
doi: 10.3788/IRLA201645.1206011
The Raman wavelength conversion was studied and numerically demonstrated which was based on the theory of forward transient stimulated Raman scattering in photonic crystal fiber, which has high nonlinear coefficient. Design scheme and implemented method of the theoretical model of all optical wavelength conversion are presented. The simulation was calculated by OptiSystem with 4 continuous probing signals. The simulation results show that the all-optical wavelength converter can convert 4 probing light in the same time, and the output signal light patterns and input pumping signal light pattern have the same waveform. Furthermore, the simulated eye diagram has a clear line and good opening degree. The feasibility is verified by the scheme.
2016, 45(12): 1206012.
doi: 10.3788/IRLA201645.1206012
The fidelity of laser target simulator is mainly used to evaluate the degree of approximation between the target simulator's output laser and the laser irradiator's output laser during its transmission and being reflected by the target surface in actual battlefield. The effectiveness of fidelity depends on the applicability and actual operability of the evaluation scheme. An effective evaluation scheme for studying the fidelity of the laser target simulator was proposed, and the quantized fidelity of every specific indicator was also defined. Firstly, the laser energy transport model of target laser in real battlefield and the control model of light spot in the hardware-in-the-loop simulator were calculated. Then, according to the two models, the fidelity evaluation content of the characteristic of laser pulse and laser spot in the laser target simulator was studied with emphasis. And finally, by calculating the weight of the specific index, the whole fidelity of laser target simulator was obtained. The fidelity evaluation scheme can be applied to the design and performance evaluation of the laser target simulator, so it can reduce the cost and time by doing the test of the laser target simulation in the hardware-in-the-loop simulation system, which means a lot in designing modern weapon system.
2016, 45(12): 1206013.
doi: 10.3788/IRLA201645.1206013
Ultrafast carrier dynamics in Al2O3/SiO2 high reflectors was investigated by UV femtosecond laser. It was identified by laser spectroscopy that, the carrier dynamics contributed from the front few layers of Al2O3 played a dominating role in the initial laser-induced damage of the UV reflector. Time-resolved reflection decrease after the UV excitation was observed by pump-probe experiment, and the peak value of the variation of the reflectivity of the probe light changed from 417 nm to 402 nm in 2.3 ps. To interpret the laser induced carrier dynamics further, a specific theoretical model including multiphoton ionization(MPI), avalanche ionization(AI), and the mid-gap defect state was built to simulate the evolution process of the electron density in the conduction band, it pointed out that during the conduction band free electron relaxation process, the mid-gap defect state locating about one photon below the conduction band was formed because of the interaction between electrons and lattice. The initial electron density effect of the mid-gap defect state has important influence to the damage threshold of the Al2O3/SiO2 high reflectors. This model agrees very well with the experimental results.
2016, 45(12): 1206014.
doi: 10.3788/IRLA201645.1206014
High power pulse laser ablation impulse effect can be used in the field of laser orbital debris removal. The recoil impulse of the space debris by laser ablation depends on the plasma plume expansion progress, and it will be changed by the change of laser ablation direction. Hence, it was necessary to study the characteristics of the plasma plume by laser ablation. Aim at the difficulties of ultra high speed, instantaneous condition, strong self luminescence and the small scale of the flow field, the technologies of ns exposure and precise stitching of multiple photos are adopted. Besides, the technology of controlling signal simultaneously with the high speed camera and laser power source was used. All these can achieve the ns scale time resolution and mm scale space resolution in the flow field quantitative measurement, which can be used to obtain the plasma plume evolution information. The plasma plume evolution characteristics of typical space debris material was obtained through experiments, also, the results of plasma plume expansion progress in different laser incident angle. The experimental results can reveal the change rule of the recoil impulse by pulsed laser ablation.
2016, 45(12): 1225001.
doi: 10.3788/IRLA201645.1225001
Terahertz(THz) Microstrip Line(MSL) is the key to THz system on chip. The rationality of the design of THz MSL affects the sensitivity and accuracy of THz on-chip system directly. To make the on-chip system better, the THz MSL and the MSL band stop filter were simulated by using the software HFSS(High Frequency Structure Simulator) by reference the theoretical model. The transmission characteristics of THz MSL and the MSL band stop filter were researched by simulation. From the point of view of application, the sample, such as GaAs, was introduced into the simulation model to research the effect of GaAs sample on the filter characteristic of band stop filter for first time. Finally, a 358 GHz MSL band stop filter was designed, and the effect of GaAs sample on the center frequency of band stop filter was discovered by changing the size of the GaAs sample putting on the band stop filter. The results of this paper provide accurate theoretical data for the design and fabrication of THz MSL.
2016, 45(12): 1225002.
doi: 10.3788/IRLA201645.1225002
Terahertz modulator, filters and absorbers are the key parts of terahertz application, while the metal split ring is the common structure of these applications. Comparisons of terahertz absorbing properties, which were caused by different structures of subwavelength metal split ring resonator, were studied by simulation and experiment. Two split ring resonators which had different split gap types were fabricated. By using Finite Difference Time Domain(FDTD) simulation and Optical Pump Terahertz Probe (OPTP) experimental methods, the terahertz transmittance curves of TM mode and TE mode were investigated when the electromagnetic waves were perpendicular to the samples. The analysis found that in TM mode, the frequency of the absorption peak was inversely proportional to the value of the effective inductance and the effective capacitance. But in TE mode, the similar resonance frequency of the two SRRs were caused by the same length of dipole resonance. In addition, when optical excitation power changed, the experimental result indicates that one-gap SRR is more sensitive than two-gap SRR in TM mode. As the pump light power up to 5 mW, the resonance frequency transmittance of one-gap SRR raised 80% than the pump light condition at 0 mW. But, two-gap SRR only raised 43% when the light condition changed from 0 mW to 5 mW.
2016, 45(12): 1225003.
doi: 10.3788/IRLA201645.1225003
Metamaterial absorbers are typically comprised by subwavelength split-ring resonators(SRRs) periodically distributed on the surface of some dielectric boarding substrates. Their absorptive rates are largely determined by the properties of the top SRRs and the material properties of the substrates. The transmission characteristics of metamaterial absorbers in terahertz wave were studied and the effect of PI thickness, cell size, width of the split ring resonator, conductivity of the top silicon and the dielectric constant of the PI medium on the position of absorption peak and absorption rate were analyzed by using the finite integration time domain(FITD) method. The characteristics of metamaterial absorber were expected to provide important reference for the design of terahertz modulator, filters, absorbers and polarizers.
2016, 45(12): 1225004.
doi: 10.3788/IRLA201645.1225004
Based on the SPICE parameters model of ideal diode, a modified small-signal equivalent circuit model of terahertz planar Schottky diode was built according to the physical structure of the diode. On-wafer device-under-test (DUT) structure based on CPW de-embed method was designed according to the equivalent circuit model of the diode. The small-signal S parameters were measured in the frequency range of 0.1-50 GHz and 75-110 GHz. All the parameters of diode model such as capacitances, resistances and inductances were extracted via the test results. Comparison between DC I-V resistances, empirical formula capacitances and high frequency parameters was made. Both of the capacitances and resistances at high frequencies were different from low frequencies. The built small-signal equivalent circuit model of terahertz planar Schottky diode was validated by simulation and the results of model simulation agree well with the DUT S-parameters. Complete equivalent circuit model and the testing method can more accurately represent the working state of the device under high frequency compared with the ideal diode SPICE model and the parameters of the traditional extraction method. This robust method is suitable for Schottky diode model extraction, which is useful for further nonlinear circuit design and optimization in terahertz wave frequencies.
2016, 45(12): 1225005.
doi: 10.3788/IRLA201645.1225005
In terahertz frequencies, using refractive index matching coupling principle, a broadband polarization splitter based on orthogonal hollow core was designed. Compared with the traditional separation device, it has the following advantages:(1) the refractive index matching degree of dual-core is high, making the separation length of the corresponding polarization mode is very short; (2) the dual-core are filled with air, which can reduce the absorption loss to THz wave; (3) through the design, making the dual-core perpendicular, thus the refractive index curve of y polarization mode overlap with that of x polarization mode, greatly expanded the scope of bandwidth. Its working bandwidth reached 0.17 THz. In addition, because of its structure is simple and symmetry, the THz fiber is easy to fabricate, which has a high application value in the terahertz network.
2016, 45(12): 1211001.
doi: 10.3788/IRLA201645.1211001
The methods of power spectrum, Zernike polynomial and Fractal used to generate atmospheric phase screens with the non-Kolmogorov statistics were introduced. Based on the three methods, non-Kolmogorov turbulent phase screens were simulated. Phase structure functions were calculated and compared with the theoretical results. In addition, the accuracy and efficiency of different methods were also analyzed. It shows that phase screen created by FFT method has the drawback of lacking low frequency, by adding subharmonics the phase screen can be compensated which also leading to the decreasing of simulation efficiency; phase screen created by Zernike polynomial method has the drawback of lacking high frequency, by using much more orders of Zernike polynomials the phase screen can be compensated which also leading to the decreasing of simulation efficiency; phase screen created by Fractal method is relatively good at both low and high frequency and the simulation efficiency is also high. In addition, the number of subharmonics and the order of Zernike polynomials under same condition of accuracy are related to the power law of non-Kolmogorov turbulent spectrum. As the spectral power law increases, the number of subharmonics increase and the order of Zernike polynomials decrease, and phase screens created by fractal method are more accurate.
2016, 45(12): 1211002.
doi: 10.3788/IRLA201645.1211002
Compressible large-eddy simulations were carried out to study the aero-optical effects caused by the flow field of a transverse hemispherical/cylindrical structure at Mach numbers of Ma=0.5-0.7. Statistic results of density and optical path difference were calculated from the density field, and the laser characteristics in far field were computed based on the phase screen method. It is found that the root-mean-square of density distortion and the root-mean-square of optical path difference increase with free stream velocity and aperture size. The one hand, with Mach number varying from 0.5 to 0.7, the root-mean-square of density distortion gain 90 percent when the aperture diameter is fixed to 0.5m, and the root-mean-square of optical path difference gain 90 percent when the aperture diameter is fixed to 0.25 m. On the other hand, with the free stream velocity fixed to 0.6, the two parameters gain 4 times respectively when aperture diameter increases from 0.25 m to 0.75 m. The laser Strehl Ratio decreases with free stream velocity and aperture size. It decreases from 0.236 to 0.045 when Mach number varies from 0.5 to 0.7 with aperture diameter fixed to 0.25 m, and it reduces 90 percent when aperture diameter increases from 0.25 to 0.75 m at 0.6 Ma.
2016, 45(12): 1211003.
doi: 10.3788/IRLA201645.1211003
The content of water vapor in atmosphere is very little, but it is the most active molecule in atmosphere. The volume ratio of moisture to air was about 0.1%-4% and most part water vapor concentration in the troposphere. The influences of atmospheric attenuation become more serious along with the development of the optics-electron detecting technology. The water vapor in the atmosphere was the main factor and uncertain parameter to affect atmospheric attenuation. Infradred wavelengths was commonly used in photoelectric detection, but water vapor makes great effect on the radiation absorption due to its high concentration. Raman lidar has become the useful advantaged tools to measure water vapor. The system structure and specifications of Raman lidar developed by introduced. The measurement results show that this lidar can take measurements of water vapor over 8 km height at night and water vapor in boundary layer in day time as well as the tropospheric aerosol in day and night continuously. The obtained results are better consistent with radiosonde data in terms of the water vapor, which assures the reliability and availability of the Raman lidar for water vapor observation.
2016, 45(12): 1211004.
doi: 10.3788/IRLA201645.1211004
Scintillation caused by atmospheric turbulence impairs the performance of the atmospheric optical communication system. Bit error rate(BER) of an atmospheric optical communication system can be improved by using an adaptive detection threshold, which is difficult to implement in real time. As a sub-optimum method, optimizing the threshold to a constant value according to statistics of parameters was proposed. Assuming multiplicative Gaussian noise and lognormal scintillation, the optimum constant threshold of an atmospheric optical communication in turbulence channel was analyzed. The result of numerical analysis was compared with experimental data obtained in weak turbulence. Results of experiment and numerical analysis show that optimizing constant threshold is necessary and the performance degradation compared to adaptive thresholding is acceptable. Neglecting aperture-averaging effects, the dependence of the optimum constant threshold on log amplitude variance and average received signal power was analyzed and the influence of other parameters was proved to be negligible. Based on previous analysis, a non-linear model was proposed to estimate the optimum constant threshold in practice.
2016, 45(12): 1211005.
doi: 10.3788/IRLA201645.1211005
The mesospheric thermal structure and temperature variations have an important scientific significance in the research of dynamic and thermal process in the middle atmosphere. The middle atmosphere temperature over the Qinghai-Tibet Plateau was measured by the Middle Atmosphere Remote Mobile Observatory in Tibet(MARMOT) lidar, which was designed and built by the Institute of Atmospheric Physics(IAP). The measurement principle, the system configuration, and the specifications of the MARMOT lidar were introduced. The middle atmospheric temperatures in summer at Golmud were analyzed using the lidar data, and the initial results of middle atmospheric temperatures were obtained. By comparing with both the MSIS-00 model data and the TIMED/SABER satellite data, the results showed that the MARMOT lidar results have a good consistency with the MSIS-00 model and the TIMED/SABER satellite results in general. In the upper and lower mesosphere, the temperatures retrieved from lidar are higher than the MSIS-00 model results and the TIMED/SABER satellite results. In the mid-mesosphere, the lidar data and the satellite data are slightly lower than model results.
2016, 45(12): 1220001.
doi: 10.3788/IRLA201645.1220001
Itegrated high-power LED light source have been applied in many practical lighting engineering, but the illumination of the integrated light source is not very satisfactory. In order to solve the problem that integrated high-power LED light source cannot be applied directly in the field of illumination, a downlight reflector and a lens was designed by using the source-target map based on the energy conservation law in non-imaging optics. These two types of optical devices were simulated in Tracepro software, which obtained a good uniform round lighting spot. The simulation results show that the illumination uniformity is reduced with light emitting area increase. The illumination uniformity of the round lighting surface is above 95% when the source size is 1 mm1 mm. The illumination uniformity is decreased to 85% when the source size is increased to 10 mm10 mm. This research is conformed with the higher uniformity standards of indoor lighting design.
2016, 45(12): 1220002.
doi: 10.3788/IRLA201645.1220002
In order to overcome the drift of Mach-Zehnder(MZ) modulator operating point by the temperature, pressure and other factors, it is necessary to compensate the voltage shift of DC bias. The previous harmonic detection method based on small dither signal has the advantage of high bias point positioning accuracy. However, a certain noise will be introduced due to the additional small signal in the loop, which will affect the purity of the radio frequency signal. The power detection working point bias method is easily influenced by the power vibration of light source, which reduces the stability and positioning accuracy of the bias point. In this paper, a MZ modulator bias point control technique was proposed, combining the average power and the harmonic detection. The optimal operating point was determined by the harmonic detection, and the ratio of the optical power before and after the electro-optic modulator was used as the reference value in feedback control. It improves the positioning accuracy and the noise performance of the bias control. Meanwhile, it overcomes the influence of the disturbance of laser power. In this method, a scheme realizing the arbitrary adjustment of bias points by controlling the ratio of optical power was also proposed and large range flexible bias point control was realized. Experimental results show that the proposed scheme has the advantages of high positioning accuracy, good stability and wide bias point, which meets well with the requirements of the MZ modulator bias point control.
2016, 45(12): 1220003.
doi: 10.3788/IRLA201645.1220003
Based on the quick start-up of fiber optic gyro(FOG) requirement is increasing for the inertial navigation system and the modern weapons, the start-up wavelength drift of superluminescent light emitting diodes(SLD) was studied, which is the slowest start-up core device in FOG. The relationship between SLD output wavelength with drive current and temperature was analyzed and verified both in theory and experiment, it was obtained that the wavelength decreases about 0.15 nm/mA with the increase of drive current and increases about 0.5 nm/℃ linearly with the increase of the temperature; The start-up model of SLD wavelength change was established by the changing law of the driving current and the core temperature of SLD after starting-up, and it was inferred that the max wavelength change was 18 000 ppm by the measurement of SLD drive current and temperature; Finally, the wavelength compensation solution was proposed to realize the quick start-up of FOG.
2016, 45(12): 1221001.
doi: 10.3788/IRLA201645.1221001
Vanadium oxide films(V2O5) were deposited under 35 min by RF reactive magnetron sputtering at the substrates of single-crystal diamond. Its structure, thickness, surface morphology, electrical performances and optical performances were studied. The results indicated that the deposited film is polycrystalline V2O5 film on(001) preferred orientation, possessing great crystallization behavior and the surface topography. In term of electrical performance, the V2O5 films' temperature-resistance characteristics were tested under three thicknesses, and the electrical mutation is best when the thickness is 150 nm. The optical-switching properties of the films were tested, and process of phase transition and recovery would occur when the films were irradiated by high-energy laser. The optical closing times range from 1.6 ms to 2.5 ms, and the response times vary from 26 ms to 33 ms, which indicate that the films' response time increases with the increase of film thickness.
2016, 45(12): 1221002.
doi: 10.3788/IRLA201645.1221002
Power delivery characteristics of fibers for high power density pulse laser makes it difficult to apply laser-driven miniflyer system into practice. In order to investigate the power delivery characteristics of fibers, an optical fiber fixture was designed in the experimental set up, which was useful to alignment of the laser beam. The transmission efficiency and damage threshold of high-peak power density laser pulses with width of 6ns and wavelength of 1 064 nm via both silica fiber and AgI/Ag hollow fibers with core diameter of 600 m are demonstrated. It is found that, within 10 mm from the focal, the average transmission efficiency of the silica fiber is 76.2%, which were 61.8% of the hollow fiber. 2 mm before the focal, the damage threshold of silica fiber and AgI/Ag hollow fiber are 22.3 mJ and 29.4 mJ. By comparing the results that, AgI/Ag hollow fiber has a higher damage threshold, its transmission efficiency is about 15% lower than the silica fiber, its engineering potential still needs to be further developed.
2016, 45(12): 1221003.
doi: 10.3788/IRLA201645.1221003
The distribution of thermal strain and curvature radius of ZnTe/Si(211) and ZnTe/GaAs(211) heterostructure samples were analyzed by theoretical calculation and laser interferometer measurement at room temperature. The results showed that the strain profiles and curvature radius of ZnTe grew on asymmetry(211) surface, are asymmetric along in-plane direction along[1-1-1] and[01-1]. The laser interference measurement result of the ZnTe/GaAs(211) sample conformed to the theoretical calculation with the radius of curvature, which are the same order of magnitude and both are in negative direction, indicating the tensile strain. But for the ZnTe/Si(211) sample, the measurement result showed much difference. The plastic deformation was formed during the high temperature deoxidation process of Si substrate, which produced heterostructure bending with positive radius of curvature. The plastic deformation of Si substrate reduced the bending degree of ZnTe/Si(211) heterostructure, so the thermal mismatch strain was also reduced.
2016, 45(12): 1216001.
doi: 10.3788/IRLA201645.1216001
The selectivity of absorption spectrum by using surface plasmonics have attracted more and more research attentions. In this paper, the periodical surface plasmonic nanostructures were presented, which consist of metal nanostructures on metallic substrate, to enhance absorption rate of ultra-high temperature metal nanostructures. The characteristics of materials' absorption have been simulated and analyzed by changing different parameters in the range of wavelength 200-4000 nm. The simulation results indicate that there always appear absorption peaks and they reach over 93% at absorption spectrum with all different parameters. The dielectric material, period, depth and size of nanostructure are the main factors for the absorption spectrum. Further, the dielectric material and period of nanostructure also have obvious selectivity characteristics on the position of absorption peak. The study results can provide theoretical foundation for ultra-high temperature surface plasmonic materials absorption characteristics.
2016, 45(12): 1233001.
doi: 10.3788/IRLA201645.1233001
To sdudy the non-visual effect to human based on the analysis of pupil contraction under low illumination LED light, ten subjects were selected to conduct pupillary light reflex test under different conditions of six kinds LED light with different colors, five kinds of low illumination. All these tests were recorded by infrared video recorder and the pupil size was calculated by the program based on OpenCV. The result shows that steady pupil contraction rate and recovery pupil contraction rate will be larger as the migration from long wave to short wave light source under the same illumination. And the non-visual effect of blue light source is the most significant. Also, steady pupil contraction rate and recovery pupil contraction rate will be larger as the illumination increased under the same light source. And there is a linear relationship between these two pupil contraction rates under the illumination of 10-70 lx with the correlation coefficient of more than 0.95. Two pupil contraction rates have a linear relationship between circadian factor, which shows that the pupil contraction rate could well represent the degree of non-visual biological effect.
2016, 45(12): 1235001.
doi: 10.3788/IRLA201645.1235001
In order to meet the requirements of honeycomb sandwich plate of an optical small satellite on the weight and stiffness, and to reduce the dynamic response of components on honeycomb sandwich plate, the equivalent theory and dynamic analysis of honeycomb sandwich plate were studied. First of all, the equivalent theory of the hexagon honeycomb core and the face sheet with adhesive layer were introduced. Then, the finite element model of -Y honeycomb sandwich plate of an optical small satellite were established, and the optimization analysis of the honeycomb core parameter with the weight and dynamic stiffness as the goal was performed. Analyzing and comparing the weight and stiffness of different core, finally, the honeycomb core of 0.03 mm in thickness and 5 mm in length was chosen. And then, on the basis of modal analysis, sine vibration and random vibration analysis are performed on the honeycomb sandwich plate. Finally, the sine and random vibration test are carried out. The experimental results and analytic solution showed that the first natural frequency error is 1.9%; the sine acceleration response error is 4.5% and the random acceleration response RMS error is 3.7%. These indicated that the analysis model is established accurately, the equivalence of parameters is reasonable and the dynamic analysis is accurate, and thus could meet the dynamic response requirements of satellite integration and each single component on the honeycomb sandwich plate.
2016, 45(12): 1231001.
doi: 10.3788/IRLA201645.1231001
Considering the limitations of low and extended trajectory and short terminal trajectory on laser terminal guidance of range extend individual rocket, the target acquisition domain and target acquisition probability of the strapdown laser guidance seeker in the whole terminal trajectory were researched. A model of target acquisition domain for semi-active laser seeker in low and extended trajectory was established. The target acquisition domain and the minimum cone field of the seeker in the whole terminal trajectory were simulated under the condition of different rocket fire angles. The position in terminal trajectory and the minimum half field angle when target acquisition domain boundary changing from hyperbolic to ellipse were analyzed, and the optimum half field angle was 5.9. Considering the influence of trajectory disturbance, the target acquisition probability of the seeker at different positions in terminal trajectory were calculated, and the optimum initial detection point of missile seeker in terminal trajectory was established by means of Monte Carlo method. The limitations of low and extended trajectory and short terminal trajectory on laser terminal guidance of individual rocket were solved. The reference for guidance of the extended range rocket projectile was provided.
2016, 45(12): 1217001.
doi: 10.3788/IRLA201645.1217001
Based Doppler shifted effect and self-mixing effect, an all-fiber photonic Doppler velocimetry was developed to solve the problem when VISAR was used to measure high-acceleration flyers, the Doppler-shifted signals often lost. Used this system to measure the laser-driven flyer's velocity at different energies. The results showed that the PDV system have a high measuring success rate, high react speed, and the calculated results is good. Compared with VISAR and F-P interference velocimetries, the PDV have many advantages such as operation more simple, high measuring success rate, easy for carrying. This system was suitable to measure the velocities of small flyers and small scale detonation which had speeds between hundreds and thousands meters per second, also the usual detonation speed measurement.
2016, 45(12): 1217002.
doi: 10.3788/IRLA201645.1217002
Bowl plugs were mainly used for plugging auxiliary holes on the engines, the processing precisions were high,required diameter tolerance was micrometer. At present the bowl plugs mechanical errors were mainly manual detections, manual detections precisions were low and can not meet the requirements of modern production online detections. Therefore proposes a method of used binocular vision to detect bowl plugs machining errors, put the bowl plugs on a rotating mechanism for constant speed rotations, two parallel cameras acquire multi groups diameter end face images. Used the proposed end face impurity removal method calibration test results, through data processing to obtain bowl plugs diameters and tapers mechanical errors. Set up a binocular vision online detection system for bowl plugs machining errors. The test results show that this method can meet the bowl plugs detection requirements and achieve online detections.
2016, 45(12): 1217003.
doi: 10.3788/IRLA201645.1217003
Target detection, recognition and identification have no uniform international standards and industry standards in video surveillance currently. Comprehensively compared and analyzed the traditional CCTV DRI standards with Johnson criteria and proposed a target observation performance evaluation method with CCTV Johnson-DRI criteria for video surveillance. Applied equivalent number of line pairs instead of the target-screen ratio in traditional analog video surveillance DRI standards. The absolute quantitative evaluation criteria were more beneficial for evaluating the performance of digital video surveillance systems. Finally, the demonstrated DRI testing in laser night vision, and the experimental results show CCTV Johnson-DRI criteria were effective and equivalent to the traditional video surveillance DRI standards. It showed this method can be using for evaluating and designing system performance for target observation in daytime color video surveillance and LED/laser night vision systems.
2016, 45(12): 1217004.
doi: 10.3788/IRLA201645.1217004
As on-orbit missions of satellites are increasingly complicated, the demand for satellites' attitude determination accuracy is becoming higher. Star sensor is the most accurate attitude sensor on the satellite, so calibration of the star sensor is critical to further improvements of satellites' attitude determination. However, conventional on-orbit method which take advantage of inter-star cosine angle to solve the calibration problem of large field-of-view (FOV) star sensor was not sufficient due to the complexity of lens distortions. Motivated by this observation, a novel technique for the large FOV star sensor's calibration based on machine learning theory was presented. The technique used the created features to build complex distortion models. These created features were redundant, so Principal Components Analysis (PCA) was employed to reduce the useless features. Moreover, two methods were employed to judge the efficiency and the effectiveness of the calibration algorithms. The results show that machine-leaning based on-orbit calibration method can achieve remarkable improvement when the distortion of the large FOV star sensor is relatively huge. The calibration error is less than 0.8 under the working condition in the paper. Compared with current algorithms, this algorithm can achieve a higher accuracy and is more robust.
2016, 45(12): 1217005.
doi: 10.3788/IRLA201645.1217005
The geometrical errors resulting from imperfection of the fabrication and assembly of two-dimensional(2D) grating were investigated. Based on the Doppler frequency shift theory and the coordinate transformation method, the general error model versus non-orthogonal and misalignment angles of 2D gratings was established. Then the effects of these error angles were quantitatively studied, and the cosine and the cross-talk errors of both directions were simulated and analyzed. The results illustrated that the geometrical errors were independent from the diffraction orders, diffraction times and the optical subdivision multiple, just determined by the error angles and the 2D displacement. Meanwhile, the cosine errors could be induced by all the error angles, but the cross-talk errors were mainly influenced by the non-orthogonal and raw angles. Besides, the cross-talk errors were more serious than the cosine errors, which is the dominant component of the geometrical errors. A planar displacement measurement system with 2D cross-grating was constructed, and the theoretical analyses and the numerical simulation were verified with the 10 mm square displacement measurement.
2016, 45(12): 1217006.
doi: 10.3788/IRLA201645.1217006
Disturbance rejection rate(DRR) not only affects output accuracy of the seeker but also worsens the performance of missile guidance system. The main factor which causes the problem of DRR with laser gimbaled seeker is the disturbing torque. Aiming at the problem caused by DRR, a real time method for compensating disturbing torque based on Strong Tracking Unscented Kalman Filter(STUKF) was proposed. With the analysis of gimbaled seeker's operational principle and disturbing torque's mechanism, the nonlinear filter model for estimating the damping and spring torque was built. The STUKF algorithm was adopted to estimate the disturbing torque quickly and accurately, and the DRR was inhibited by the proposed method. Finally a math simulation and a hardware-in-loop simulation were put forward, the simulation results indicate that the accuracy of the seeker's output and stable performance of guidance system are improved after the disturbing torque is compensated.
2016, 45(12): 1217007.
doi: 10.3788/IRLA201645.1217007
In order to improve the accuracy of centroiding for high precision miniature star tracker, a method to calibrate the imaging sensor pixel displacement using heterodyne laser interferometry was proposed. And the star position error due to imaging sensor pixel displacement was studied by simulation. The simulation results show that the accuracy of star position can be enhanced from 0.008 pixel to 0.002 pixel by compensating pixel displacement when pixel displacement obeys uniformly distributed over the interval (-0.02, 0.02) pixel. When the additive Gaussian noise in the star image has a normal distribution with mean 0 and standard deviation 5.5, if pixel displacement obeys uniformly distributed over the interval (-0.02, 0.02) pixel, the accuracy of star position can be enhanced from 0.020 pixel to 0.018 pixel after compensation; if pixel displacement obeys uniformly distributed over the interval(-0.04, 0.04) pixel, the accuracy of star position can be enhanced from 0.026 pixel to 0.018 pixel after compensation, which are 31% better than the accuracy without compensation. Simulation results show that calibrating pixel displacement which can significantly improves the star position accuracy can be used as a new method to develop high precision miniature star tracker.
2016, 45(12): 1217008.
doi: 10.3788/IRLA201645.1217008
A multi-functional high-precision comprehensive diagnostic system for laser parameters was developed. The entire diagnostic system was composed of a fundamental frequency laser diagnostic module, a tripled frequency laser diagnostic module, an online optic damage inspection module, an opening frequency conversion unit and corresponding auxiliary units. Under the control of the system software, it can automatically perform accurate measurement, data collection, storage and processing on laser parameters such as near-field, far-field, energy, wavefront and pulse-waveform before and after the laser frequency conversion. This system provides accurate data for improving laser facility load capacity and researching relevant key unit technology.
2016, 45(12): 1217009.
doi: 10.3788/IRLA201645.1217009
Airborne LiDAR system is a multi-sensor integrated system, including laser scanner, global positioning system, inertial navigation system, and so on. One of the key point to obtain high positioning accuracy of laser point cloud is the airborne LiDAR calibration. And the installation angle error of laser scanner is one of the main factors which influence the measurement accuracy. Based on the working principle of airborne LiDAR system, a domestic medium range system Mars-LiDAR was developed. According to the error propagation law, the effects of measurement error and hardware installation error were analyzed. A method using different calibration field to separate installation angle errors between laser scanner and inertial navigation system was proposed. At the height of 3 000 m and 4 000 m, the high positioning accuracy was obtained, satisfying the specifications of data acquisition of airborne LiDAR. Finally the test data verified the utility, reliability and feasibility of the error calibration method by using practical engineering application.
2016, 45(12): 1217010.
doi: 10.3788/IRLA201645.1217010
The method full absorbing is the most commonly technique to measure total energy of high energy laser(HEL), which is one of important technical indexes for parameters test of HEL. In order to improve the ability of laser damage resistance, in comprehensive consideration of work mode and temperature field distribution of energy absorbing graphite, a novel HEL rotational calorimeter was designed. The calorimeter especially applicable to laser long-time irradiation has a series of advantages, such as low measurement uncertainty, uncomplicated configuration and environmental adaptability. Numerical simulation results through method of ray tracing show that laser energy loss is less than 0.3 percent. The software based on finite element method was used to analyze temperature field distribution and maximum of absorb material, rotate speed-dependent temperature, temperature curve at the different positions of temperature sensor. Simulation results indicate that the calorimeter can be applied to several ten million joule(MJ) energy of HEL successfully, and provides a novel technique way for measurement of higher laser energy.
2016, 45(12): 1218001.
doi: 10.3788/IRLA201645.1218001
To evaluate the performance of large telescope under different kinds of error source, the normalized Point Source Sensitivity (PSSn) was introduced, which is firstly studied by the group of Thirty Meter Telescope(TMT) team to balance all the deviation of the telescope and also budget the error. First and foremost, character of the normalized PSSn was studied specifying the advantage in the evaluation in all the frequency domain. Then, the PSSn was compared with the traditional metric(FWHM, Strehl ratio, MTF, etc.). And the multiplication property was discussed. Using of Zernike polynomials allowed linking PSSn to the static error faced by large telescope, and the dynamic one was linked to PSSn by MTF. Lastly, the method was applied to a large telescope. Under mechanical vibration, the PSSn of this telescope main mirror decreased from 0.996 to 0.991. It aimed to guide beginner in the field of large telescope in the error analysis field.
2016, 45(12): 1218002.
doi: 10.3788/IRLA201645.1218002
Multi conjugate adaptive optics (MCAO) has been widely used in the large ground-base astronomy telescope, since it can enlarge the field-of view(FOV) and reduce the effect of atmospheric anisoplanatism. Only considering the anisoplanatism, with the assistance of the multi-thread adaptive optics simulator (MAOS), the difference of a conventional adaptive optics(CAO) and a MCAO system at the wavelength of 0.6 m and 2 m was studied respectively, it is quite obviously that in the visible band there is a significant improvement of the MCAO system than the conventional AO system. The influence of the second deformable mirror(DM) conjugate height was also discussed which had a key influence on the performance in the visible band, while the first one conjugated at the entrance pupil, and a preliminary study of the effect of DM order in the single adaptive optics system was provided in the end.
2016, 45(12): 1218003.
doi: 10.3788/IRLA201645.1218003
The infrared scene simulator based on digital micro-mirror device(DMD) can test the performance of infrared imaging system by simulating the infrared radiation of the real object and environment in the indoor environment. A set of the infrared zoom projection system with dispersion prism was designed by ZEMAX optical software. The system can match the different viewing angle of the system and avoid overlapping between projection systems and illumination systems on the space. The system can work for the band of 8-12 m. The F number of the system is 2.7. A zoom optical compensation way was used in the system. And the system can realize the focal lengths of 50/100/150/200 mm through four zoom blocks. According to the principles and Gaussian optics formula of four-component system sub-group compensation, the optical parameters of the system were counted; the initial structure which was similar to the optical parameters was adopted and then optimized. The design results show that the image position is stable and the modulation transfer function(MTF) curve at 20 lp/mm of each focal length is closed to the diffraction limit during zoom process,which could conform to the requirements.
2016, 45(12): 1218004.
doi: 10.3788/IRLA201645.1218004
In order to meet the requirements of the surface error RMS value and stiffness of GEO(Geostationary Earth Orbit) laser communication primary mirror subassembly, the subassembly structure was optimized. Firstly, the optimal design of 9 group parameter combination of primary mirror was conducted by orthogonal optimization method, instead of total 81 group combination, avoiding repeating parameter optimization and heightening the efficiency of optimal design, in which the surface error RMS value on 1 g gravity and the one on 2℃ radial temperature difference were satisfied with /50(=632.8 nm) surface error demand, the RMS value under 5℃ uniform temperature rise can be improved. Secondly, the flexure support was optimized. The simulation result showed that the first order fundamental frequencies is 213 Hz, superior to 200 Hz fundamental frequency, the maximum surface error RMS values of 1 g gravity on three directions, 5℃ uniform temperature rise and 2℃ radial temperature difference is 10.78 nm, lower than surface error demand. The test demonstrated that the RMS value under 5℃ uniform temperature rise is 7.27 nm, less than design requirement. The optimal design provided technical support to process and alignment of primary mirror subassembly.
2016, 45(12): 1223001.
doi: 10.3788/IRLA201645.1223001
In order to explore the feasibility of accurate identification between crop and weed species using polarization spectroscopy, Field Imaging Spectral System (FISS) was utilized with a polaroid configuration to collect imagery data of corn and five kinds of weeds in the laboratory. Through comparisons and analysis of spectral response curves, characteristic difference and identification model accuracy between corn and weeds under four polarization angles, it was found that there was a consistency for spectral changing trends between corn and five kinds of weeds, and the spectral intensity of corn and weeds displayed highest in the no polarization status. Moreover, the selected sensitive bands under four polarization conditions to distinguish corn and weed species indicated that there were similar characteristics, as well as some differences. Finally, for overall accuracy of the identification models between corn and weeds, and the corresponding Kappa coefficients were all more than 90%. The accuracy was the highest, close to 100%, when data were measured at 0 polarization angle. Therefore, polarization technology can be used to identify corn and weeds on the leaf scale, providing an important data foundation for further application on a field scale.
