2017 Vol. 46, No. 3
column
- Invited paper
- Space debris detection
- Infrared technology and application
- Laser technology
- Laser technology and application
- Optical communication and optical sensing
- Photoelectric navigation and control
- Advanced optical materials
- Photoelectric device and microsystem
- Optical design and simulation
- Laser radar technology
- Photoelectric measurement
- Spectrum detection and analysis
2017, 46(3): 302001.
doi: 10.3788/IRLA201746.0302001
The coupling effect in three dimensional measurements using optical microscopy refers to the phenomenon that the accuracy of the measurement height of a groove or step sample that suffers a principle error caused by the influence of the relatively small transverse period of the sample. Based on the convolution irrelevance principle and the limited energy lost principle, two models depicting the coupling effects in measurements of the thin step samples and the deep groove samples were established respectively, thus the coupling relationship between the geometric parameters of the sample and the measurement capability of the optical instrument were revealed. Compared with the existing W/3 reading rule, this criterion can more objectively reflect the different influences of samples with different structures on the actual measurement capability of the optical instrument, and indicate the assessment portions for height measurements without accuracy loss, also is able to predict the generation of principle error in height assessment if the structure is too tight or deep, thus provides a new reading and evaluation criterion for the three dimensional measurement of a groove or step sample.
2017, 46(3): 329001.
doi: 10.3788/IRLA201746.0329001
High precise measurement of space debris is an important way to improve the precise surveillance and collision prediction for space debris. As one of space debris measuring technology based on the ground-based electro-optic telescopes, laser ranging is the most accurate. According to characteristic of laser ranging to space debris and aiming at the international technical development, through the development of high power laser system and the breakthrough of high efficiency laser signal detection, the space debris laser ranging system with the aperture of 60 cm telescope was set up as the pioneer in the development of laser measurement to space debris in China. The routine laser measurement of space debris were implemented with the measured distance from 500 km to 2 600 km, cross section from less than 0.5 m2 to more than 10 m2. According to the laser ranging link equation of space debris, combining with the statistic of laser echoes, and considering the sunlight arcs of space debris orbit when passing through the ground station, the detection simulation model of ground-based laser ranging system were constructed. The evaluation of detected ability of space debris laser ranging system with 60 cm aperture telescope was also performed with the capability of measuring debris at the distance of 1 000 km and diameter of more than 50 cm which accorded with the actual measurement results. The simulation models of laser ranging to space debris will lay the foundation for the ground-based laser ranging system with high efficient running and development of observation equipment and evaluation of detection efficiency in future.
2017, 46(3): 329002.
doi: 10.3788/IRLA201746.0329002
Impulse coupling effect of short pulsed laser ablation the target has great application in the fields of laser ablation micro-thruster and laser orbital debris removal. High precision impulse measurement is the necessary method in studying the impulse coupling effect. The torsion pendulum with laser interferometer method was put forward and the measurement system was constructed. In light of the problems of vertical axis vibration and existing error angle in the initial state of torsion pendulum, the high frequency vibration will lead to the non uniform spacing in laser interference fringes, besides, the initial angle will lead to the bright stripe advancing, these two factors will lead to the low measuring accuracy. An impulse experimental data analysis method was put forward based on ordinary least squares techniques, which can remove the high frequency noise effectively. The method can solve the problem of low measuring accuracy and improve the micro impulse method.
2017, 46(3): 329003.
doi: 10.3788/IRLA201746.0329003
The growing number of space debris threatens the flight safety of manned space station and satellites. In 2011, NASA proposed to use a continuous ground-based laser station irradiation to change orbit of space debris. The photon pressure is slight but durable, and accumulates to a considerable orbit change. The orbit change will avoid the possible collision. This method does not bring the space debris back into the atmosphere, but to prevent the collision. For the method, the spacecraft is no need to maneuver for space debris collision avoidance, and the mild photon pressure just need median power laser generator. Thus, the method gets widespread concern in recent years. However, the head-on irradiation control law in this method is simple, but not the best. It is necessary to design the optimal control law. Through the establishment of two point boundary value model to maximize the distance between two objects for control objectives, and then solving the optimality conditions, the optimal control problem is solved. The simulation shows that the modified control law has been optimized to improve the performance of collision avoidance, and the degree is very significant, concerning to the initial orbit of the space debris to avoid collision, it is usually 25% to 125%.
2017, 46(3): 329004.
doi: 10.3788/IRLA201746.0329004
Two typical materials of small scale space debris in LEO were selected. On this basis, corresponding laser ablation impulse coupling models were established respectively. The velocity variation of the space debris irradiated by high-power pulsed laser was analyzed, and the orbit transfer of the small scale space debris irradiated by laser was modeled and investigated. The variations of the orbital parameters of the space debris orbit under the irradiation of laser with assumed power were simulated and analyzed, and the influence rules of the spinning angular velocity and laser with different power on debris removal efficiency were analyzed and discussed. The simulation results show that the space-based laser of assumed power can complete the mission of removing two typical materials of debris successfully by irradiating in one cycle of flight, which provides necessary theoretical basis for the application of space debris removal by using space-based laser.
2017, 46(3): 329005.
doi: 10.3788/IRLA201746.0329005
In-orbital spacecraft has been in great danger because of centimeter space debris. Nowadays a research topic that high energy laser irradiates orbital debris to make it into the atmosphere burned down has been more and more hot. In order to take care of centimeter space debris near space station, a space-based system with high energy laser had been appeared, with a method of calculation of multiple pulses laser orbital-dropping. The simulation result shows that the possibility of removing space debris with space-based laser is that space debris is in a certain condition named cleaning window. The selection of cleaning window is the key of orbital-dropping of debris. Under the existing conditions, such as laser power and platform parameters, multiple pulse laser orbital-dropping of debris is feasible. The result of multiple pulses laser orbital-dropping shows that debris orbital parameters have a big change in eccentricity and a small change in inclination, causing a big range in perigee and a small range in apogee. After insuring range of orbital-dropping, the result of single pulse velocity increment is nearly close of multiple pulses. Because the orbital-dropping has a great difference, there cannot be calculated of orbital-dropping by a single pulse to approximate multiple pulses. Based on above discussion, the modeling and simulation of detection and removing centimeter space debris with space-based laser system can be finished.
2017, 46(3): 304001.
doi: 10.3788/IRLA201746.0304001
The skin infrared (IR) characteristics of a Unmanned Aerial Vehicle (UAV) is the most important basis for the detection and recognition of the UAV. And the aerodynamic heating of an UAVskin, the heat transfer by solar radiation and earth radiation are the key factors that are contribute to the skin IR characteristic of the UAV. The skin IR characteristics calculation model of an UAV was built based on the environment infrared radiation and that of the UAV in this work. The one-dimensional heat conduction difference equation of the UAV skin was found out by a forward-difference method. And then, based on which, the IR radiation intensity distribution of the UAV in a certain plane was calculated by importing the skin emissivity of an UAV. Finally, it is concluded that the IR radiation intensity of an UAV at 8-14 m band is far greater than that at 3-5 m band. And at the same band, the radiation intensity of the top skin is higher than that of the bottom skin.
2017, 46(3): 304002.
doi: 10.3788/IRLA201746.0304002
Aiming at the lack of target texture information in infrared target tracking, strong coupling between the target and the background, and the case of occlusion causing that the characteristic information cannot be extended, the anti-occlusion algorithm for infrared target tracking with salient feature space was proposed. Firstly, by analyzing the characteristics of the infrared target, the salient feature space was generated by using multi-scale saliency, contrast and information entropy, and the regions were clustered with the super-pixel feature distance and spatial distance to highlight the infrared target area. By quantifying the different regions of the infrared image, the saliency map was generated. Based on the saliency map and the original image, a plurality of target candidate regions was generated as the tracking algorithms input. Finally, the spatial distribution field matrices of the infrared target were matched by way of the global candidate regions. At the same time, the occlusion detection mechanism on account of the change of the salience regions and the inter-frame variation curve of feature similarity was established. Experimental results on different IR test sets show that the proposed infrared target algorithm can achieve better tracking performance under the occlusion condition, which effectively enhances the robustness of the tracking algorithm.
2017, 46(3): 304003.
doi: 10.3788/IRLA201746.0304003
The noise model and characteristics of the infrared detector in low temperature background were analyzed and experimentally researched. Detector noise calculation model and method of four parameters method were used in this paper. The experimental platform was set up for test the performance of the infrared detector under different low temperature. Results of the relationship of the low-frequency temporal noise, high frequency temporal noise, low frequency spatial noise, high frequency spatial noise respectively with temperature and integration time were obtained. Within a certain temperature range, experiments prove that low frequency temporal noise shows a strong correlation with temperature, low frequency spatial noise exhibited obvious nonlinear response of detector, high frequency noise is dependent on integration time significantly.
2017, 46(3): 305001.
doi: 10.3788/IRLA201746.0305001
For the limitation of single-wavelength laser interference in military electro-optical countermeasure, the composite output program of dual-wavelength laser was proposed, providing an efficient way for universalization of military electro-optical countermeasure equipment. With the theory of steady state and rate equation, the composite output model in both continuous and pulsed output conditions were established. The result of numerical simulation shows that there exists optimal KTP length in both continuous and pulsed conditions. While the best fundamental-wavelength(FW) transmissivity only exists in continuous condition. Through the experiment, the relationship between FW transmissivity and output ratio of composite laser was verified. The effect of repetition rate on output ratio is then explored in experiment.
2017, 46(3): 305002.
doi: 10.3788/IRLA201746.0305002
Dye-doped cholesteric liquid crystal laser was designed and manufactured, and the output characteristic of the device was measured and analyzed. The cholesteric liquid crystal laser device of planar alignment state texture was prepared by doping laser dye DCM and chiral compound S-811 into nematic liquid crystal TEB30A. By using doubled frequency 532 nm Nd:YAG pulsed laser as pumping source to pump the device, the band edge lasing emission was obtained at 607 nm and 680 nm. The line-width was less than 0.5 nm. Then the energy threshold characteristic of the laser and the energy distribution of the lasing spot were measured and analyzed. In the liquid crystal device, photonic density of states is greatest at the edge of the photonic band gap, threshold is lower and laser radiation is obtained easily.
2017, 46(3): 305003.
doi: 10.3788/IRLA201746.0305003
New coupler Q switch rate equations were obtained by taking account that the intracavity photo density and the initial population-inversion density are both ellipse Gaussian distributed. The space dependent rate equations were solved numerically. The key parameters like maximum energy, optimized reflectivity, and optimized small signal transparency were determined under the ellipse Gaussian distribution approximation, and a group of general curves were generated for the first time. The optimal calculations for a diode laser near end pumped passively Nd:YVO4 laser was presented to demonstrate the use of the curves and related formulas, the maximal pulse energy of 1.5 J, peak power 81 W, and pulse width 18.4 ns can be obtained when small signal transparency T0 is 75% and reflectivity 91.8% after calculation. The pulse energy of 1.25 J, peak power 76.4 W and pulse width 16.3 ns was obtained by using a saturable absorber with 73.4% small signal transparency and a 87% reflector in experiments. Experiments agree with theoretical results well.
2017, 46(3): 305004.
doi: 10.3788/IRLA201746.0305004
1.5 m LD pumped erbium ytterbium co-doped phosphate glass passively Q-switched microlaser was currently laser ranging military hotspots, and to achieve high laser pulse energy was particularly important. Experimental study of miniaturized laser was using of 940 nm diode laser as the pump source, Er3+/Yb3+ co-doped phosphate glass as the gain medium, Co2+: MgAl2O4 as a Q-switched laser crystal miniaturization. In order to obtain LD-pumped erbium ytterbium co-doped phosphate glass microlaser passively Q the best energy output condition, factors of the LD-pumped erbium ytterbium co-doped phosphate glass passively Q-switched laser output pulse energy were analyzed. A lot of experiments were done on pump laser output power conditions, the length of the gain medium, the output mirror transmission and other parameter. Eventually stable laser output was obtained with wavelength of 1.535 m, single pulse energy of 13 J, pulse of 6 ns, repetition rate of 10 Hz, beam quality of 1.2.
2017, 46(3): 305005.
doi: 10.3788/IRLA201746.0305005
Single frequency fiber laser is the most promising optical source in fibre optic communication, which plays an important role in fibre optic sensor, laser radar and laser range finde. Generally, the performance of the single frequency fiber laser was evaluated by the phase noise. The oscilloscope and dynamic signal analyzer method were adopted to design phase noise of single frequency fiber laser. Using power spectrum and the integral sources of different pump power, seed source power and wavelength of the fiber laser phase noise were analyzed qualitatively, the results show that, the greater pump power can get the low frequency phase noise. For the different seed source powers, phase noise is in the proportion of basic test frequency at the same level. For testing seeds of different wavelengths which is different proportions of high frequency phase noise, the biggest percentage of seed wavelength is 1 560.48 nm.
2017, 46(3): 306001.
doi: 10.3788/IRLA201746.0306001
APD arrays provide an efficient method for photon detection probability improvement. However, the noise detection probability increases as well as the echo detection probability. Properly choosing the unit number of APD arrays means a lot for signal-to-noise ratio (SNR) improvement. In this article, according to the photon detection probability in the Geiger-mode, the SNR model with the unit number N was established based on the distribution of echoes and noise within the range gate. Effects of number of echoes, noise rate, location of echoes and fill factor were discussed. Analytical results show that larger number of echoes, higher fill factor and more precise orbit prediction help increase the SNR with APD arrays. 4-unit APD arrays are enough for laser ranging with echo number smaller than 0.1 and noise number within the range gate smaller than 1, while when there are large number of echoes and noise, 25-unit APD arrays will achieve a better SNR. The established SNR model for APD arrays will help for proper unit number selection to achieve the best SNR.
2017, 46(3): 306002.
doi: 10.3788/IRLA201746.0306002
In order to verify the reliability of the velocity measurement by microwave modulated laser technologies, a system of microwave modulated laser velocity measurement was developed. In the system, laser as carrier was intensity-modulated by microwave signal, transmitted the signal intensity was directly detected by the receiver on a movement platform. After the signal processing, the Doppler frequency shift data was obtained, from which the relative velocity was obtained. Meanwhile, the average velocity as the third party data was calculated by measurements of the movement distance and time, which was used to compare with velocities calculated by Doppler shift. The theoretical analysis and verification experiment are presented and the results show that the velocities calculated by Doppler shift are in good agreement with the third party velocities with a mean deviation of 2.0%.
2017, 46(3): 306003.
doi: 10.3788/IRLA201746.0306003
The precise measurement of the birefringence in the liquid crystals has significant meaning for practical applications. The working principles of the liquid crystals were analyzed. The laser anisotropy external cavity feedback system was built based on the laser feedback effect. The anisotropy of the liquid crystals under different voltages was measured. The measurement results show that the accuracy of the laser anisotropy external cavity feedback system is within 0.3°; By imposing different voltage from 0 to 24 V, the birefringence changes from 2.74×10-1 to 2.39×10-3, corresponding to the large range phase retardation of 460° to 5°. With the voltage in the range of 0.7 V to 2 V, the relationship between the voltage and the birefringence is linear and its linearity is better than 95.5%. The liquid crystals can provide stable phase retardation, the short-term repeatability is better than 0.52° and the long-term repeatability is better than 4.5°.
2017, 46(3): 306004.
doi: 10.3788/IRLA201746.0306004
In order to overcome the difficulties of the large aperture laser system, combining the output energy of multiple laser beams with small aperture at the target surface was a feasible scheme. To meet the target surface requirements for the uniformity and symmetry of the irradiation, the synchronous control precision of multi-pulse was analyzed in detail. The results show that multi-pulse irradiation affects the synchronization of the energy distribution center in far-field directly. While one single beam pulse delay is greater than or equal to 2 times of the pulse width, the peak value of the light intensity on the target surface will fall down to 75%. If the control errors of two pulses are occurred with the same degree peak value of light intensity will fall down to 50%. Otherwise, when the control error of the pulse width is twice as large as the ideal pulse width, the peak value of the intensity on the target surface will drop to 87.5%.
2017, 46(3): 322001.
doi: 10.3788/IRLA201746.0322001
The Rayleigh Brillouin Optical Time Domain Analysis system has the advantages of single source, single ended operation and non destruction. In order to solve the contradiction between the system signal-to-noise ratio and the spatial resolution, the coding technique was applied to the Rayleigh Brillouin Optical Time Domain Analysis system and a simplex code Rayleigh Brillouin Optical Time Domain Analysis sensing system based on the Avalanche Photo Diode detector was presented. The Rayleigh Brillouin Optical Time Domain Analysis system applied coding technology can improve the signal to noise ratio while maintaining the same spatial resolution. In the system, the random shot noise power was related to signal power, and the thermal noise power that was irrelevant to signal power mainly depended on the performance of the Avalanche Photo Diode detector. By analyzing the variance of current volatility which was relevant to two kinds of noise and Simplex code encoding and decoding rules, the mean square error of coding system was obtained, then the signal-to-noise ratio and coding gain formula were deduced. With the increase of coding length, the coding gain was also increased, then stabilized at a stable value, so the system had the optimal coding length. Finally, the optimal coding length formula was deduced. By using MATLAB it is verified that as the coding length increases, the coding gain tends to a stable value of 6.69 dB when the first-order Rayleigh scattering light power is 0.5 mW in the Rayleigh Brillouin Optical Time Domain Analysis system based on Simplex code, and the optimal code length was 63 bit.
2017, 46(3): 322002.
doi: 10.3788/IRLA201746.0322002
A two-channel fiber optic sensor based on surface plasmon resonance was developed. The effects of two materials of Au and Cu on the performances of the fiber optic sensor modulated by incident wavelength were analyzed. The thickness of metal was optimized, and the optimized thickness of the metal dAu=47 nm and dCu=53 nm was chosen to carry out numerical simulation. And the results show that, the sensitivity of the channel of Au is higher than the sensitivity of the channel of Cu, on the other hand, the detection precision of the channel of Cu is four times higher than the detection precision of the channel of Au. The sensing channel of Au is suitable for the detection of the lower refractive index of sensing medium, and the sensing channel of Cu is suitable for the detection of higher refractive index of sensing medium. The proposed sensor has expanded the detection range, compared with the single channel sensor. The detection accuracy of the two-channel SPR fiber sensor is higher than that of the single channel sensor. The measuring sensitivities of two-channel SPR fiber sensor and conventional single channel sensor are the same.
2017, 46(3): 322003.
In order to realize long propagation length, a two-layer dielectric-loaded surface plasmon polaritions(TDL-SPPs) waveguide was proposed． The mode field distributions and propagation properties of the TDL-SPPs waveguide were studied by using finite element method(FEM). The waveguide sensitivity was also studied. The results show that the propagation length of the proposed TDL-SPPs waveguide is 2.4 times as much as that of the conventional dielectric-loaded surface plasmon polaritons(DL-SPPs) waveguide. The TDL-SPPs microring resonator based highly sensitive biosensor was demonstrated. The results show that the sensitivity is more than 411 nm/RIU and the detection limit is less than 1.210-5 RIU. The design and research on the biosensor based on TDL-SPP microring resonator is a valuable exploration in biosensing application with high sensitivity.
2017, 46(3): 322004.
doi: 10.3788/IRLA201746.0322004
When a partially coherent beam is transmitted in turbulent atmosphere channel, the optical intensity scintillation effect caused by atmospheric turbulence can be effectively suppressed, and accordingly performance of communication link is improved. According to Gamma-Gamma atmospheric channel model and characteristics of partially coherent beams, the analytic expressions of average bit error rate(BER), outage probability and average channel capacity were obtained for partially coherent optical communication system. Based on these results, the influence of spatial coherence length and communication distance on performance of communication link was analyzed. Numerical results show that as the spatial coherence length of a partially coherent beam decreases, the system BER and outage probability decrease gradually under the same atmospheric turbulence conditions and transmission distance, and the outage probability is lower than 10-6 and system BER is 10-5, when average signal-to-noise ratio (SNR) is 30 dB; Meanwhile, as the spatial coherence length of the partially coherent beam decreases, average channel capacity of the system increases, and the average channel capacity is up to 3.8 b/sHz-1 when SNR is 12 dB. The analytical results provide a theoretical basis for the realization of the communication of partially coherent light in the turbulent atmosphere.
In order to study the effect of seeker disturbance rejection rate on performance of optimal guidance law, based on guidance law with terminal impact angle(GLTIA) and extended guidance law with terminal impact angle(EGLIA), the regularization of strapdown seeker disturbance rejection rate on the stability of guidance system was studied. Using adjoint method the miss distance of GLTIA and EGLIA were analyzed. The results show that the stable domain of guidance system is larger when strapdown seeker parasitic loop is negative feedback than positive feedback, the stability will reduce when the value of disturbance rejection rate gets bigger. Though EGLIA has more excellent guidance performance than GLTIA, but the influence of a parasitic loop of seeker disturbance rejection rate will be more serious, the sufferable value of seeker disturbance rejection rate for EGLIA is about 2.5%, and the GLTIA is about 3.5%. In the practical application, if the guidance law would work with advanced performance, the value of seeker disturbance rejection rate should be much stricter to reduce the effect of parasitic loop.
2017, 46(3): 331002.
doi: 10.3788/IRLA201746.0331002
Disturbance rejection rate (DRR) not only affected output accuracy of the seeker but also worsened the performance of missile guidance system. The main factors which caused the problem of DRR with semi-strapdown imaging seeker were scale error and disturbance torque. Firstly, a model of guidance system which contained disturbance rejection rate parasitic loop (DRRPL) was established. The relationship between DRR caused by different factors and the stabilization of guidance system was analyzed on basis of the model. Then, an online rejection method based on strong tracking unscented kalman filter (STUKF) was proposed to solve the problem above. The nonlinear filter model considering DRRPL was built by working principle of semi-strapdown seeker, the STUKF algorithm was adopted to estimate DRR and real line of sight rate. Finally, a math simulation was put forward. The result indicates that the guidance accuracy is improved after the compensation of DRR, and the compensation method had good anti-interference and robustness. The above theoretical analysis can provide guidance for online identification and compensation of semi-strapdown seeker disturbance rejection rate.
2017, 46(3): 321001.
doi: 10.3788/IRLA201746.0321001
An evaluation method of real photonic crystal fibers(PCFs) based on compressed sensing with Contourlet transform was proposed for evaluating optical properties of PCFs. Integrated with the total variation denoising method, only 48% cross-section data of PCFs can be used to reconstruct the whole cross-section of PCF, and the edge features of air holes in multi-scale and multi-direction were also effectively preserved. The classical images, a large mode area PCF and a polarization maintaining PCF product were used to verify the effectiveness of the proposed method. Experimental results demonstrated that the cross-section images of real PCFs can be effectively rebuilt by 48% cross-section data. To the best of our knowledge, it is the first time to apply the compressed sensing with the Contourlet transform to reconstruct the cross-section images of PCFs for evaluating the optical properties of real PCFs.
2017, 46(3): 321002.
doi: 10.3788/IRLA201746.0321002
The relationship between the emissivity of millimeter wave stealthy coat, the real temperature of target surface and some typical environment emissivity was calculated; based on that, the emissivity value range expression of three color millimeter wave stealthy coat was deduced with the typical environment emissivity. The relationship between the color block emissivity value ranges with the real temperature of target surface was discussed in three different cases. The result shows that in the 300-400 K, the main color emissivity value should be similar to the environmental emissivity(for the ground, g=0.935), the harmonize emissivity value changes monotonically with the target surface real temperature; they have the same value range, and decrease with the increase of the target surface real temperature. The conclusion plays a guiding role in designing the millimeter wave stealthy coat.
2017, 46(3): 321003.
doi: 10.3788/IRLA201746.0321003
A distributed acoustic sensing (DAS) scheme was presented. Rayleigh backscattered light which contained acoustic signal induced phase changes along the sensing fiber was fed into a Michelson interferometer, the phase changes were demodulated by the Phase Generated Carrier technology. A piezoelectric simulation experiment of acoustic vibration was designed. The DAS system realized 10 m location resolution of the acoustic source, and the flat frequency response through the experiment.
2017, 46(3): 321004.
doi: 10.3788/IRLA201746.0321004
The nonlinear absorption properties of borate glass doped with CdS0.2Se0.8 nanocrystal (RG665) were investigated using Z-scan and pump-probe techniques with femtosecond pulses. It was found that RG665 showed strong nonlinear absorption under 130 fs laser pulses at 800 nm wavelength. By theoretically analyzing the experimental results, the nonlinear absorption of RG665 included two parts: two-photon absorption and the excited state absorption induced by two-photon absorption at 800 nm wavelength. The two-photon absorption coefficient was obtained to be about 0.05 cm/GW, the excited state absorption cross section was e=310-23 m2, and the electron lifetime on the low energy state and bottom in conduction band was 13 ps and 210 ps respectively. The research results certify that the borate glass doped with CdS0.2Se0.8 nanocrystal is a good kind of nonlinear optical material.
2017, 46(3): 321005.
doi: 10.3788/IRLA201746.0321005
KDP crystal is the chief choice of frequency multiplier in high power laser system. Laser pretreatment is usually used to improve the damage probability of KDP element, the pretreatment process is more time-consuming, and it is of great significance to the engineering application to improve the pretreatment efficiency. KDP damage performance preconditioned by different laser pretreatment protocols was investigated, every protocol had three key parameters: laser radiation fluence, irradiated laser shots, and energy steps. By analyzing the condition parameters and the resultant damage performance, effect of every parameter on damage performance was discovered, and it is found that the same pretreatment performance can be achieved by using different energy steps, and laser pretreatment protocol was optimized by using variable energy steps instead of fixing one. Experimental results show that the variable energy steps protocol achieves total laser shots savings of 33%. The results would be benefit for KDP elements pretreatment process.
2017, 46(3): 320001.
doi: 10.3788/IRLA201746.0320001
Grating shaft of a double grating spectrometer is an important part which is used to fix and drive gratings, deformation and vibration of which both have effects on final measurement result. According to operating principle and working condition of the double grating spectrometer, centroid adjustment, light weight, avoid resonance and the decrease of the random vibration were chosen to be main goals in the optimization. First, three-dimension model of concave gratings, grating shaft and its fixture were built in UG. Then, they were imported into ANSYS Workbench, modal analysis and random vibration analysis were done. Finally, multipurpose optimization was done according to the result in last step. After the multipurpose optimization, centroid of the rotating parts was adjusted to the rotating axis. Its mass reduced from 0.606 30 kg to 0.539 43 kg. Its second natural frequency increased from 184.83 Hz to 187.77 Hz, and the maximal random vibration deformation on Z axis of concave gratings reduced from 33.394 m to 27.147 m. Centroid adjustment of structure could be realized directly by common finite element analysis software, the author achieved this goal when building three-dimensional models, and guaranteed that centroid of the rotating parts moved only on their rotating axis in optimization, so that centroid adjustment and light weight can be realized at the same time, which can be widely used in many other projects.
2017, 46(3): 320002.
Affected by the factor of atmospheric turbulence and spatial optical coupling efficiency in the satellite-ground coherent optical, its extraordinarily difficult to achieve high data rate and high detection sensitivity of communication. In view of the difficulty of spatial optical coupling in the satellite-ground coherent optical communication link, the method to improve the detection sensitivity by using large area balance detector was proposed. Based on the analysis of the balance detection technologys principle and structure, the balance detector with a diameter of 100 m and a working speed of 5 Gbps was designed, and the simulation test platform of the spatial coherent optical communication was built. Under the communication rate of 5 Gbps, the direct detection sensitivity of the detector is -18.6 dBm, the coherent detection sensitivity is -43.89 dBm, and the common mode rejection ratio is above 38.5 dB. The test results verify the feasibility of the spatial coupling balance detector for coherent optical communication.
2017, 46(3): 318001.
doi: 10.3788/IRLA201746.0318001
With unique working principle and spectral characteristic, the long wave infrared (LWIR) interferometric spectral imaging is a popular technology with wide application in many fields. In order to miniaturize and light the instrument, a new method of LWIR spectral imaging system based on a variable gap Fabry-Perot (F-P) interferometer was researched. With the system working principle analyzed, theoretically, it was researched that how to make certain the primary parameters, such as, the reflectivity of the two interferometric cavity surface and the wedge angle of interferometric cavity. A prototype was developed and good experimental results of blackbody and polypropylene film were obtained. The research shows that besides high throughput and high spectral resolution, the advantage of miniaturization is also simultaneously achieved in this method.
2017, 46(3): 318002.
doi: 10.3788/IRLA201746.0318002
A partial field optical system baffle was designed and optimized. Partial field was non-symmetry along one direction, so a large number light tracing was needed to design the centric, which made it difficult to design. A method of footprint diagram was used to get the coordinate of special light in the space, the size of effective field and the part of baffle blocking light. The part blocking light was removed and a duck mouth shaped baffle was got, which can decrease the difficulty of design. By optimizing the design, length of final designed baffle was half of the former one, and reduced the size along Y direction, which can reduce more stray light to enter the later optical system directly. Baffle was modeled and simulated by Solidworks and TracePro software, the PST is about 10-9 when the off-axis angle is 30, which is less than 5.5910-7, the requirement of the system. The result of the simulation shows that using method of footprint diagram to design inner baffle of a partial field optical system is feasible.
2017, 46(3): 330001.
doi: 10.3788/IRLA201746.0330001
When lidar is used to detect atmospheric visibility, if cloud, fog, smoke, dust or the hard target exist in the detection path, the atmospheric extinction coefficient will change significantly in the local area, then the lidar return signals occur mutate against the original attenuation trend along with distance. Affected by it, using existing algorithm directly will cause the accuracy of visibility inversion low or wrong inversion. A combination visibility inversion algorithm including breakpoint location, extinction coefficient boundary value determination, extinction coefficient iterative inversion was proposed. Firstly, the breakpoint signal was found and located; Secondly, breakpoint was excluded by using slope method to acquire extinction coefficient boundary value; Finally, atmospheric extinction coefficient and visibility based on Fernald algorithm were inverted. According to the simulation experiments of two kinds of typical atmospheric extinction model, the accuracy of visibility inversion is improved, the more accurate global visibility is obtained. The validity of the proposed algorithm is also been verified by using real return signals of the lidar visibility meter developed by ourselves.
2017, 46(3): 330002.
doi: 10.3788/IRLA201746.0330002
Aiming at airborne multi-pulse laser radar target echo waveform irradiated by the nanosecond pulse width laser, the geometric section ratio feature is proposed, which is insensitive to target attitude and can be used for target detection and tracking combined with target motion state information. And then, the feature extraction algorithm is given. Firstly, by analyzing the relationship between target waveform and target features based on the laser target waveform model, it is pointed out that geometric section ratio of laser target is an attitude insensitive feature. Next, for the separation of target waveform from noises without distortion, the improved Donoho threshold de-noising algorithm is given in wavelet domain using discrete wavelet transform, the target waveform sequence length is obtained with wavelet reconstruction signal, the peaks of target waveform are detected through first order and second order difference equations, and then laser target scattering center and geometric section ratio can be extracted. Finally, the performance of the proposed algorithm is verified through simulation experiment. In the test with airborne multi-pulse laser target simulator, the laser target multi-frame matching detection experiment is developed, using the features which are extracted by the algorithms proposed in this paper and combining with the target motion state information.The multi-pulsed laser target detection become more reliable.
2017, 46(3): 317001.
doi: 10.3788/IRLA201746.0317001
Eddy current thermography technique was adopted to detect micro cracks near surface of ferromagnetic materials. The method of parallel excitation and heat conduction was put forward to detect micro cracks near surface. The process of heating in cracks using eddy current thermography was simulated by numerical calculation. The temperature distribution around the crack and the influence on the detection results were analyzed. The parallel excitation was adopted for the detection test. The surface temperature distribution curve of the specimen was extracted, and the slope curve was got by differential. Finally, the detection and recognition on cracks were realized. The results show that the parallel excitation method of eddy current thermography can have an efficient detection on micro cracks near surface of ferromagnetic materials, and appropriate excitation time can contribute to the rise of the temperature contrast and the enhancement of the testing effect. All the above researches lay a foundation for the detection and quantitative identification of micro cracks near surface.
2017, 46(3): 317002.
doi: 10.3788/IRLA201746.0317002
In order to meet the real-time demand in on-machine inspection of machining center and calibrate the parameters of line structured-light plane with high efficiency, low-cost and high precision, a calibration method of light plane was proposed based on the planar target with concentric circles. Through moving freely the planar target at several arbitrary positions in the field of the cameras view, 3D coordinates of points on the line structured-light plane could be calculated by the calibration method integrated with the model of perspective-three-points (P3P) and the principle of cross-ratio invariance, then the equation of the line structured-light plane was fitted by least square method(LSM). Experiments showed the methods validity and feasibility by the analysis of calibration and inspection accuracy. It concludes that the method is suitable for the machining and inspecting field calibration with advantages in its simple algorithm and the flexible calibration process.
2017, 46(3): 317003.
doi: 10.3788/IRLA201746.0317003
The measurement method based on laser-aided machine vision has been widely used in 3D shape measurement for large-scale components and parts at present. To solve the problem of the inaccurate extraction for components boundaries, a high-precision method of 3D shape measurement for large-scale parts was proposed in this paper. Firstly, an adaptive light stripe locating method based on time flow was proposed according to the sequence of acquiring images, by which the region of the light stripe can be located in real time. Next, a boundary detection method based on light stripe mutations was presented to acquire the row or column coordinates of the object boundaries in the light stripe. Then the coordinates of the boundaries can be determined precisely combined with the extraction results of light stripe centers. And the effective light stripe centers for measurement within the two determined boundary feature points can be retained. At last, the extracted light stripe centers were matched and reconstructed to accomplish 3D shape measurement. Experiment results show that the measurement accuracy of this method reaches 0.06 mm and precise boundary information of objects can be acquired. The cost of computation is also reduced greatly. Thus, the proposed method can satisfy the measurement requirements of high precision and rapid speed.
2017, 46(3): 317004.
doi: 10.3788/IRLA201746.0317004
A fiber grating acceleration sensor based on flexure hinge structure was designed. The structure theory analysis was carried out and the finite element model was built to simulate and analyze the acceleration sensing characteristic of the sensor. A fiber Bragg grating(FBG) acceleration detection system with temperature self-compensation was designed based on F-P filter, which achieved zero temperature self-compensation by adding a feedback circuit to control F-P filter. The characteristics of the system were tested on the built system. The results indicate that the system has excellent response to impulse excitation signal and continuous acceleration excitation signal. Natural frequency of the system is 380.0 Hz, while the dynamic range reaching 65.6 dB. The frequency response range of the system is 10.0 -240.0 Hz, in which the acceleration sensitivity is 236 pm/g. Since the sensitivity in the interference direction is only 3.5% of the sensitivity in the working direction，the acceleration sensor is designed with strong lateral immunity.
2017, 46(3): 323001.
doi: 10.3788/IRLA201746.0323001
Underwater multispectral imaging is a promising technique for high-fidelity underwater color reproduction and mapping of kelp, sea grass, corals, etc. However, as light propagates through water, light is severely absorbed and scattered by water, causing image dim, hazy and distorted in its spectrum and color. In this paper, calibration of water attenuation coefficient based on underwater images and restoration of underwater multispectral images are discussed. Multispectral images of an underwater object are captured at different underwater distances. Technique has been proposed to calibrate the water attenuation coefficient based on underwater images of different distances and restore the raw images. Analysis was also conducted to search for the least number of distances for coefficient calibration and restoration. By comparing the restored underwater images with the images captured in air, its found that the technique proposed in this paper provides accurate restoration of underwater spectral images, with a relative residual error of 5.87% in average for all test images.
