2017 Vol. 46, No. 2
column
- Invited paper
- Combustion field detection and analysis
- Laser technology and application
- Laser technology
- Infrared technology and application
- Information acquisition and identification
- Optical design and simulation
- Atmospheric optics
- Micro-nano optics
- Optical communication and optical sensing
- Photoelectric measurement
- Spectrum detection and analysis
- Photoelectrical device and materials
- Photoelectric devices and material
2017, 46(2): 201001.
doi: 10.3788/IRLA201746.0201001
Vortex beam is a new kind of beams with helical wavefront. It has an annular intensity distribution,and with orbital angular momentum(OAM) related to the helical wavefront. The OAM state of a vortex beam can be any integer, and vortex beams with different OAM states are mutually orthogonal, which indicates the potential of enlarging the capacity of optical communications. However, when a vortex beam propagates in free space, its wavefront will be distorted by the turbulence of the atmosphere. It is necessary to study how to compensate the wavefront distortion by using adaptive optics system. In this paper, some adaptive optics correction approaches were summarized. Moreover, schemes of correcting distorted vortex beams, which were proposed by our group, were introduced. One scheme was the pre-compensation method by using the GS algorithm and a Gaussian probe beam. The other one was a phase correction method by using a Zernike polynomials-based SPGD algorithm.
2017, 46(2): 201002.
doi: 10.3788/IRLA201746.0201002
Single molecule fitting-based super-resolution imaging methods achieve nanoscale image resolution but suffer from a long time resolution. The long acquisition time is limited by the low molecule density of fluorescent molecules that can be localized per imaging frame. In this paper, a fast compressed sensing method was proposed to use random sampling operator, together with the block compressed sensing reconstruction method, have a good performance of localization accuracy under high molecular density and reconstruction speed.
2017, 46(2): 239001.
doi: 10.3788/IRLA201746.0239001
Diagnosis of combustion field was mainly useful to structure designing and combustion state organization of the combustion chamber. Laser schlieren/shadow and difference interferometer were used to study the wave structures of combustion field. And combustion border and combustion violent region were diagnosed by the planar laser-induced fluorescence of OH groups (OH-PLIF) method to get a clear field of combustion wave lines and the combustion results displaying by PLIF. Combining laser shadow/difference interferometer and OH-PLIF, the relationship between the wave lines and combustion could be seen. To cut the image of light source similarly to traditional schlieren by adopting a new laser schlieren technology, which produced not obvious laser speckle and diffraction phenomenon. What's more, it was meaning to display the wave structure and diagnosis by PLIF at the same time. The work above can be a reference for the study of supersonic combustion fluid field.
2017, 46(2): 239002.
doi: 10.3788/IRLA201746.0239002
Cavity ring down spectroscopy(CRDS) is an absorption spectroscopy technique with high sensitivity, which is a very important quantitative concentration measurement approach in combustion spectral diagnosis. The principle analysis of CRDS was presented to apply to absolute concentrations of intermediate species in flames, and then an experimental setup of pulsed CRDS was established based on this principle. The absolute OH concentration was measured by using absorption on the P1(2) rotational line in the A2+-X2(0,0) band of OH on a plat flame at atmospheric pressure. Influence of several major factors on the measurement uncertainty was analyzed, such as laser line shape and linewidth, frequency stability of the laser, flame temperature, and cavity parameters. This uncertainty analysis provides several guidelines to improve the measurement accuracy of CRDS.
2017, 46(2): 239003.
doi: 10.3788/IRLA201746.0239003
Combustion driven chemical laser system has a number of key species in ground states such as DF molecules which can characterize the performance of the combustor of chemical lasers. Additives such as SF6, NH3 and H2O may be added into chemical lasers as collisional particles in order to control the relaxation processes of vibrational-rotational excited states of hydrogen fluoride molecules. There are also some key intermediate species such as NF(a) which could interact with vibrational-rotataional excited states of hydrogen fluoride molecules via near-resonant energy transfer processes. However, the absorption coefficients of these key species are generally very small. In order to obtain the absorption spectrum of the ground state of these key species, an off-axis cavity enhanced absorption spectroscopy apparatus was established. The apparatus consisted of the light source, the optical resonator and the photoelectric receiver, wherein the resonator was built within a vacuum chamber. In order to verify the performance of the device, the absorption spectra of trace amounts of ammonia and water vapor were measured. The results showed that the noise equivalent absorption coefficient of the device reached 1.610-8 cm-1. The experiment results show that the cavity enhanced absorption spectrometer can be used to obtain the number densities of those key species in HF chemical lasers.
2017, 46(2): 239004.
doi: 10.3788/IRLA201746.0239004
Experiments were conducted in a newly designed constant volume combustion bomb with orifice plate by varying initial conditions. Hydrogen-air mixtures were used to obtained the turbulent flame front and shock wave, as well as the processes of flame-shock interactions were tracked by high-speed schlieren photography. The effects of apertures, porosities, equivalence ratios and distance between spark and orifice plate on the flame propagation speed, the intensity of shock wave and their interactions to pressure oscillation were analyzed in detail. It was found that there formed a clear shock wave after laminar flame passing through orifice plate under certain conditions.The reflected shock wave interacted with the flame front, which causes oscillating flame propagation. On the other hand, the cylinder pressure presents a violent fluctuation. It was indicated that the interaction between flame and shock wave was the reason of pressure oscillation. This work provides a references for the study of knock in SI engines and shows a method for DDT and pulse detonation phenomena research as well.
2017, 46(2): 239005.
doi: 10.3788/IRLA201746.0239005
To research the influence of quasi-DC transversal electrical discharge plasma on the fuel jet flowfield in the combustor of scramjet under the pulse control, the pulse quasi-DC transversal electrical discharge plasma model was established. Under different pulse excitation frequency, taking advantages of numerical simulation, the influence of plasma on the formation feature of cavity fuel jet flowfield, loss of combustor total pressure, the mixing efficiency of the jet downstream was analyzed. The results show that, under pulse plasma condition,the position and intensity of the upstream separation shock can be controlled effectively, the periodic fluctuation of the cavity flowfield due to the pulse control, which improved the mixing efficiency of the fuel and mainstream, can decrease the total combustor pressure losses contrast to steady control.
To explore the effect of 830 nm semiconductor low-level laser on the acupoints and myofascial trigger points(MTrPs) of patients with upper back myofascitis. In pre-experiment, 23 patients with upper back myofascitis were collected and divided into 4 groups including laser 1, laser 2, laser 3 and acupuncture group. In 3 laser groups, semiconductor laser therapeutic apparatus invented by our research team were used to treat patients(wavelength 830 nm, power density 0.335 W/cm2) for 1 min, 2 min and 4 min every time separately; in acupuncture group, puncture at Yanglao point(SI6), Chengshan point(BL57) bilaterally, as well as MTrPs. All patients were treated 3 times per week and for 4 weeks. In formal clinical study, 38 patients with upper back pain were collected and treated with laser for 4 min. The visual analogue scale(VAS) and short-form Mcgill Pain questionnaire-2(SFMPQ-2) were used to assess the symptoms of patients, and pressure pain threshold(PPT) was examined by hand-held algometry. Results In pre-experiment, except the laser 1 group, the VAS score reduced significantly after treatment in other three groups(P0.05). Comparing the efficacy with each other of all the groups, the best is acupuncture group, followed by laser for 4 min group. As SFMPQ-2 was concerned, the score decreased significantly only in acupuncture group(P0.05). Laser therapy can increase the PPT of MTrPs of patients. In formal research, the score of VAS and SFMPQ-2 were reduced significantly by 830 nm laser therapy. The symptoms of soreness, tenderness and sense of tired and powerlessness were improved by laser. The PPT of MTrPs were also improved. Conclusions semiconductor laser therapeutic apparatus invented by our research team can improve the subjective scoring and semi-objective PPT, can be used in clinical treatment widely.
2017, 46(2): 206002.
doi: 10.3788/IRLA201746.0206002
For satellite laser ranging(SLR) with high repetition rate, the interference of atmospheric backscattering on the echo receiving has been more serious by the increase of measuring rate, and has become one of the key factors which restrict the maximal working frequency of SLR technology. According to the atmospheric scattering radar detection equation, the received optical power of atmospheric backscattering from a certain distance was analyzed. Based on the platform of bi-static SLR system in SHAO, the rationality of theory was verified by interference experiment of atmospheric backscattering. According to the theory, making clear production mechanism of backscattering interference, backscattering avoiding methods on the basis of controlling laser emitting epoch were presented. With a module for outputting laser fire signal integrated into range-gate generating circuit with high repetition rate, and the control of the laser firing delayed by judging the existence of backscattering in real time, the backscatter auto avoiding circuit was finally completed based on FPGA. Now it has been successfully applied in the routine SLR measurement of SHAO, the average fire frequency reduction rate has been lower than 2% for most important satellites such as Lageos, and will has a very good propagation and application value.
2017, 46(2): 206003.
doi: 10.3788/IRLA201746.0206003
Laser spot center location algorithm of four-quadrant detector based on Gaussian distribution was proposed to improve the accuracy of real-time laser spot center location measurement in FPGA. Firstly, the laser spot used Gaussian distribution model was equivalently analyzed. Combined with working principle of the four-quadrant detector and a reasonable set of Gauss integration interval, light energy of each quadrant can be calculated. Corresponding to the photocurrent in the same area, Gaussian distribution equations containing location information were deduced. And then, by using the standard Gaussian distribution table, laser spot center location expressions were derived quickly which made the algorithm be implemented in hardware in real time. Finally, simulation and experimental verification were carried out with the algorithm which was based on Gaussian distribution and circular model respectively. The results show that the precision of the algorithm based on Gaussian distribution is increased by 43.8%. Thus, it proves that this algorithm can effectively improve the accuracy of spot center location measurement.
2017, 46(2): 206004.
doi: 10.3788/IRLA201746.0206004
Researches on the laser deposition repair of aircraft vertical tail beam with mis-machined damage were investigated. According to the mechanical characteristics while its serving, the samples of mechanical properties were designed and the tensile properties at room temperature of laser deposition repaired sample and substrate sample were analyzed. Besides, microstructure characteristic, microhardness distribution were also analyzed. The results showed that there was a dense metallurgical bond between repaired zone and substrate. And the laser repaired zone experienced a continuous microstructural transition from duplex microstructure with equiaxial and lamellar / in substrate to the epitaxial coarser columnar with basket weave / through heat-affected zone. And the repaired zone was characterized by a fine / lamella microstructure without defects. Distribution of microhardness from substrate to repaired zone showed an increasing trend, and the average microhardness of repaired zone increased by 12%. Whether the tensile specimens with holes or not, laser repaired samples tensile strength were slightly higher than substrates, but the ductility were lower than substrate. Based on the optimized process parameters, the causes of edge collapse defect on the repaired sample were analyzed at the same time and the ideas to reduce defects were given to enhance the deposition quality.
2017, 46(2): 206005.
doi: 10.3788/IRLA201746.0206005
In view of the fact that the output of line of sight angular rate error was big in the test of certain laser seeker, it was pointed out that line of sight angular noise root in the detector noise together with bomb disturbing and friction moment. Then stable tracking loop model was built based on the control principle of the laser seeker, the influence of above-mentioned error on tracking performance and los angular rate of the laser seeker was quantificationally analyzed. The characteristic of los angular rate noise of the laser seeker was analyzed, the function relationship with distance between missile and target was deduced by experiment method. Finally, the los angular rate noise was joined into control and guidance model of the laser guided missile. Simulation result showed that roll angle of missile and rudder departure angle varied obviously, angular noise changed small gradually along with the close up of missile and target and the miss distance varied less, which was accordant with actual test phenomenon. When the angular instruction was situated in the peak value of the angular noise, deviation of missile couldn't be modified timely, which possibly affected attack area of missile along with close up of missile and target. The research provids reference for further actual test of laser seeker and tactical application of missile.
2017, 46(2): 206006.
doi: 10.3788/IRLA201746.0206006
Because the depth information of pavement could not be got directly by traditional method of pavement detection, a detection method for the depth of broken block in pavement based on 3D laser scanning technology was presented. The point cloud data of the broken crack can be obtained by a 3D laser scanner. The crack data can be divided into several slices along the horizontal direction, and the depth information for each of the slices can be estimated by the distance between the up and down planes respectively. According to the practical engineering, a novel plane fitting iterative algorithm based on dynamic threshold was proposed, it can not only identify and remove invalid points in the point cloud data effectively, but also accomplish plane calculation with errors in three directions. Experiments show that the proposed method can not only get the depth information of the whole pavement broken block, but also reflect the change trend of the depth of the broken block along the horizontal direction.
2017, 46(2): 206007.
doi: 10.3788/IRLA201746.0206007
The displacement measurement based on single mode in HeNe laser with the birefringence optical feedback can output two feedback signals. The fringe phase difference is not affected by the feedback external cavity length, so it has great potential in the development of large range and high resolution displacement measurement system. Phenomenon of birefringence optical feedback was researched and displacement measurement system of high-performance was developed. The frequency stability and anti-jamming capability of the displacement measurement system were improved by combining the frequency stabilization technique and feedback cavity scanning technique. The stabilized frequency fluctuation was less than 10-7. The zero drift, beat frequency and comparison of the system were tested. Its range was more than 200 mm, the resolution is 15.82 nm, the linearity is better than 2.310-7. The main error sources of the system were analyzed, and the total measurement error was 0.21 m. The displacement sensor features compact configuration, nanometer-scale resolution, good linearity and large measurement range, and has broad application prospects in industry.
2017, 46(2): 205001.
doi: 10.3788/IRLA201746.0205001
A burst-mode laser diode driver(LDD) with dual-loop power control circuit was designed for the passive optical network(PON) applications. The charge compensation and dynamic bias circuit was employed to reduce the rising and falling time of the output current and enlarge the output current capability. A dual-loop power control feedback circuit was proposed to avoid the variations of average power and the extinction ratio with temperature. The proposed laser diode driver was implemented in a 0.18m RF CMOS technology and the chip area was 1 600m800m. Experiment results show that the output bias current and the modulating current can reach 90 mA. The burst-on time of the LDD is less than 2 ns and the burst-off time is less than 1 ns with 2.5 Gbit/s data transmitting rate and 41 ps magnitude. The average power stability and the extinction ratio stability of the LDD is 0.26 dB and 1 dB, respectively. The proposed LDD meets the needs of the optical power and stability of the laser for PONs.
A laser diode(LD) end-pumped adhesive-free bond composite Nd:YVO4 Acousto Optical(AO) Q-switched and RTP Electro Optical(EO) Q-switched laser were reported at the same experimental condition. TEM00 operation of 1 064 nm laser were obtained at repetition rate of 500 kHz in AO Q-switched regime and 200 kHz in EO Q-switched regime. And it was the first time to compare the output performance of AO Q-switched operation and RTP EO Q-switched operation at high repetition rate. In EO Q-switched regime, the average output power reached to 12.13 W with the pulse-width of 16.65 ns. In AO Q-switched regime, the average output power reached to 13.56 W with the pulse-width of 27.27 ns. The experimental results show that RTP EO Q-switched operation has better performance of turn-off. However, due to limitation of high voltage driver, EO Q-switched is not able to achieve with shorter pulse width and higher peak power laser under higher repetition rate operation. The AO Q-switched operation that has better output characteristic at higher repetition rate, and it would be the preferred method to obtain Q-switched laser which the repetition rate is high as thousands of hundreds and even mega.
2017, 46(2): 205003.
doi: 10.3788/IRLA201746.0205003
Parasitic oscillation in the slab amplifier affects the efficiency of laser amplifier and reduces the stored energy of slab crystal. The surface of Nd:YVO4, gain of grazing incident slab amplifier was processed to suppress the parasitic oscillation in the slab and improve the energy storage ability of slab crystal. Through ion sputtering method, the germanium was plated on top and bottom surface and the back surface to suppress the parasitic oscillation. In germanium plated and without germanium plated conditions, the slab oscillator's output characteristics were compared between free oscillation and Q-switched mode, threshold current reduced 15% in plating germanium slab oscillator, and the stored energy improved 86.9%. The beam quality, pulse duration and spot pattern of plating germanium slab oscillator were basically the same to without plating germanium slab oscillator in Q-switched mode. Experimental result indicates plating germanium on the face of slab is an effective method to suppress the parasitic oscillation and improve the energy storage ability of crystal.
2017, 46(2): 205004.
doi: 10.3788/IRLA201746.0205004
Based on the Fresnel-Kirchhoff's integral theory, the three-dimensional near filed and far filed light intensity distribution of non-chain pulsed DF laser with unstable resonator was obtained using Fast Fourier algorithm. Numerical calculation shows that the mode pattern is ring shaped at near field and multistage diffraction ring with central bright spot at far field,and the near field spot laser intensity will be concentrated as M increases, while the far field angle of divergence will increase with the increment of effective Fresnel number(Neq). Then the influence of mirror tilt on near-field light intensity distribution is investigated, indicating that the beam in near field will be deteriorated when misalignment appears, the larger of the tilt angle the much more obvious of asymmetric light distribution. The measured light intensity distribution on near-field and far-field and the variation of near filed light intensity distribution with mirror tilt angle are consistent with the simulation results, and the far-field divergence obtained is 1.2 mrad. The simulation results can provide a basis for cavity mirror misalignment diagnostic analysis and resonator regulation of non-chain DF laser.
2017, 46(2): 205005.
doi: 10.3788/IRLA201645.0205005
In order to study the thermal characteristic of output window during the working process of high power CO2 laser, a time-dependent model coupled with heat transfer and structure mechanic was established to calculate the distribution of temperature, thermal deformation and thermal stress. First, the physics characteristic of output window materials was discussed. Then, based on the resonant cavity structure of 10 kW TEA CO2 laser and the physics characteristic of output windows, a heat transfer and structure mechanic model was established. Finally, COMSOL finite element software was used to calculate the distribution of temperature, thermal deformation and thermal stress. The influence of different materials of output window on parameters was analyzed. The results indicate that the temperature rise of ZnSe output window is less than the GaAs output window when the output power is consistent for both materials; the deformation of output windows is in the range of m dimension under the 10 kW laser power condition; the distribution of thermal deformation and thermal stress is more even in GaAs output window for its high heat transfer coefficient.
2017, 46(2): 204001.
doi: 10.3788/IRLA201746.0204001
In order to study the effective working distance for shipboard infrared sensors, according to the definition and features of Lambert radiation source, based on the scientific analysis for surface battleship's infrared radiation, a calculation model was put forward for ship's infrared radiation power on specific band range and on specific direction. The model fully considered the double property, namely being as a point source and simultaneously as a surface source, the power calculation formula was put out under different directions with the help of relative radiation table. In order to validate the model's effectiveness, the FLIR infrared imaging equipment was used to carry out the relevant experiment. The results show that the calculated working distance from the model witnesses a good agreement with the experimental results. The model can serve as a basic gauge for studing the working distance of shipboard infrared sensors under bad-weather conditions.
2017, 46(2): 204002.
doi: 10.3788/IRLA201746.0204002
The high speed imaging processing module based on MWIR cooled 320256 detector, SDRAM memory and other function module circuit was designed for time-sharing type polarization imaging system. Processing module mainly included the driver board connected to detector, processing board with FPGA as its core, system power supply board. The algorithm of blind pixels compensation, nonuniformity correction, plateau histogram equalization and linear mapping were implemented, calibration parameters can be calculated online. Image processing module can realize the synchronization switch, integral time adjusted continuously, frame rate up to 200 fps, and output 320256 pixels high quality infrared image, meeting the requirement of the polarization imaging system to detect moving objects. Infrared polarization imaging experiments on plastic cups with groove were carried out, effective Stokes parameter images were extracted from the polarization images, and the significant polarization properties were observed. The processing module can be applied to the detection of space target, mine detection, maritime search and camouflage target detection.
2017, 46(2): 204003.
doi: 10.3788/IRLA201746.0204003
Fourier infrared spectrometer and thermal imager can be used to measure infrared spectra and image of conventional liquid rocket plume flow field. The infrared spectral of plume flow field was detected, the main products of combustion H2O, CO2, and traces of combustion products NO and N2O were measured. The plume flow field structure was captured by infrared image, the relationship between the image characteristics and combustion state was set up. The results show that the infrared spectrometer and infrared thermal imager can accurately measure characteristics of plume flow field combustion products, the flow field structure and the application of infrared technology for the engine work condition monitoring provides a new analysis method.
2017, 46(2): 204004.
doi: 10.3788/IRLA201746.0204004
In order to study the influence of lobed mixer on infrared(IR) character of serpentine 2-D exhaust system(S2ES), three different lobed mixer S2ESs with lobe numbers of 12, 15 and 18 were designed. The influence of lobe number on IR suppression of S2ES was studied numerically, and the results were compared with a relevant annular mixer S2ES. The results show that, as the lobe number increases, thrust rises slightly with the maximum difference less than 0.1%; the reduction of lobe number changing from 18 to 12 enhances the mixture of core flow and bypass flow and reduces the plume temperature, making the plume radiation intensity attenuated by 18.1% at most; compared with annular mixer S2ES, the radiation intensity of lobed mixer S2ES reduces at least 20.9% and 26.9% in the direction vertical to the axis of nozzle exit on the side and lower detection planes respectively. In summary, it is appropriate to use mixer with fewer lobes in order to achieve better IR suppression.
2017, 46(2): 204005.
doi: 10.3788/IRLA201746.0204005
IR optical system of roll-elevation seeker was composed of object lens front group, turning mirrors group and imaging rear group. The pitch frame had 90 moving range and the roll frame had 360 moving range, so that the combination of rolling and pitching enabled the optical system to realize all over the front hemisphere field. The optical system achieved 100% cold shield efficiency. In order to adapt to the large variation of working environment temperature, the athermal design was used, and the formulas to realize athermal design were given. By using the technique named dummy chromatic aberration, the best initial solution of athermal design was found quickly. For controlling the Narcissus effect of this cooled IR optical system, the formula to compute the NITD were given, and the sensitive surface of Narcissus effect was optimized. The design result showed that the optical system working parameters were the effective focal length of 58 mm, field of view of 4.0, F/# of 2.0, and the MTF of the optical system was close to the diffraction limit when working temperature changed from -50℃ to 60℃. The narcissus effect was also controlled effectively. The optical system met the design requirements by imaging test.
2017, 46(2): 226001.
doi: 10.3788/IRLA201746.0226001
In the dynamic tracking mode of a star sensor, the signal noise ratio(SNR) of the shifted star image attenuates resulting in difficulty of dim star extraction. When the number of extracted stars drops to 2, attitude error increases. Obviously for the dynamic star image the aligned pixel gray superposition method was incapable of increasing its SNR remarkably, so a novel inter-frame shifted window gray superposition method was proposed instead. This novel method raised the gray level and the SNR of a dim star by means of superposing pixel gray of inter-frame window area, in a shifted style rather than an aligned one, during which the gray data of the shifted windows of several successive frames were stored into a cache in a pipeline mode. So the peak gray value of a dim star was enhanced and turned to be over the detecting threshold, and no less than 3 stars in the FOV can be finally guaranteed to be used in attitude calculation. The simulation results manifest that the SNR of the dim star image is increased more than 1 times after applying the new algorithm with 4 frames, thus a higher precision can be achieved by the three-star improved attitude determination due to the added one star.
2017, 46(2): 226002.
doi: 10.3788/IRLA201746.0226002
Current PM2.5 model forecasting data greatly deviate from the measured concentration. In order to solve this problem, support vector machine (SVM) was applied to set up a dynamic model. The data of PM2.5 model forecasting (WRF-CHEM) concentration and the five main model forecasting meteorological factors were used as training data of SVM. The data were provided by Shanghai Meteorological Bureau in Pudong New Area (from November in 2012 to November in 2013). The dynamic model was used to improve the forecasting accuracy of PM2.5 concentration one hour in advance. SVM model was compared with radical basis function neural network (RBFNN), Multi-variable Linear Regression (MLR) and WRF-CHEM. Experimental results show that the proposed algorithm greatly improves the forecasting accuracy of PM2.5 concentration one hour in advance. SVM model performs better than RBFNN, MLR and WRF-CHEM, and has better forecasting ability for the condition with concentration dramatic changing.
2017, 46(2): 226003.
doi: 10.3788/IRLA201746.0226003
Earth observation systems can quickly detect objects in a large area, which offers great convenience for ship detection and monitoring by the coastal countries in the world. Towards the automated ship detection in remote sensing images, a method that made use of the salient contrast between ship and sea was proposed. Thus, the ship detection and segmentation problem was converted to a salient object discovery and location problem. Inspired by the biological process of visual pathway from the retina to the primary visual cortex V1, the visual signal generating mechanism was simulated to acquire the saliency map of the scene. The experimental results, obtained from using optical images, show that the contrast based method can effectively concentrate on the ships in the sea without any prior knowledge. It is noteworthy that the proposed method achieves good results.
2017, 46(2): 218001.
doi: 10.3788/IRLA201746.0218001
One of the important direction of the optical system is the co-aperture optical system, which takes advantage of optical system characters with long-focus and high resolution. This paper designed a tracking guiding system whose aperture of the optical system for visible light imaging, laser imaging and laser ranging was shared. The co-aperture design combined the high resolution visible light system with high resolution laser system, which made the system not only obtain high-definition images, but also get the relative location information. The co-aperture optical system could compress system size, reduce the rotational inertia when the optical system was in the process of tracking for the overall implementation of the system. The focal length of visible light subsystem is 1 200 mm; F number is 6; field of 1.2. The focal length of laser imaging subsystem is 1 500 mm; F number is 7.5. Each system imaging quality is close to the diffraction limit, and tolerance allocation results is verified by tolerance analysis.
2017, 46(2): 218002.
doi: 10.3788/IRLA201746.0218002
To make up for the poor monochromaticity and the narrow energy range of particle source which is applied at the demarcation of domestic detector in aerospace probe, a precision control mirror bracket driven by the piezoelectric ceramic motor for Compton optical source was designed. In order to impinge accurately with high energy electron beam and obtain the continuous changed peak energy of the particle, the input angle of the laser beam was adjusted exactly with the elastic deformation of the flexure hinges. The mathematic model of stiffness and displacement in both latitude and longitude directions were developed by the principle of the pseudo-rigid-body model. Then, the displacement in both directions and the distributing rule of the stress were discussed through the finite element analysis, and the simulation results indicate that the structural parameters are fully satisfied. Finally, it was confirmed experimentally that the adjustable angles of the precision control mirror bracket both are 1.12in latitudinal and longitude directions, and the positioning accuracy is not less than 610-4.
2017, 46(2): 211001.
doi: 10.3788/IRLA201746.0211001
In order to solve low sensitivity of flow visualization using a single-pass schlieren system under the conditions of higher Mach number, low static pressure, the double-pass schlieren system with 900 mm caliber of light beam of spherical mirror in China, was developed. Compared with a single-pass one, higher sensitivity was obtained, and more flow detail can be provided and the range of application of the schlieren technique can be expanded through a double-pass schlieren system. The out-of-focus flow image was eliminated by replacing colorful knife edge with the LED light source of the four-color-light, by adding the compensating lens, optimizing object lens and adjusting finely the LED light source. The flow image on the common aviation vehicle(CAV) model obtained using double-pass schlieren system was compared with that obtained using single-pass schlieren one. The incident diaphragm was added before the object lens so that a light spot was removed. The vivid flow image on the big blunt model was obtained under experimental condition of Mach number 10, total pressure 2.0 MPa, total temperature 1 100 K, angle of attack from 0 to 15. The advantage and disadvantage of a double-pass schlieren system was analyzed.
2017, 46(2): 211002.
doi: 10.3788/IRLA201746.0211002
Due to the limitation of wind tunnel test capability, it was very hard to be completely consistent with the actual flight of high speed aircraft. As an important similarity number, Reynolds number had been used widely in classical fluid mechanics wind tunnel experiments. It had a significant impact on establishing aero-optical similarity standard to study the influence on aero-optics induced by Reynolds number. Based on the theorem, the possible variables that affected aero-optics were analyzed, which verified Reynolds number was a similarity standard value of aero-optics. A creative experimental equipment was designed to realize the unit Reynolds number ranging from 106-108 m-1. Eight typical Reynolds numbers were chosen, BOS-WS (BOS-based Wavefront Sensor) technique was used to measure the corresponding optical path difference. Based on the function curve fitting method, the power function between Reynolds number and the rms of the optical path difference was acquired. The measured results with different sizes were compared. It could be found that, for the two dimensional supersonic film, the acquired law was not affected by the size of the observed aperture.
2017, 46(2): 216001.
doi: 10.3788/IRLA201746.0216001
Raman scattering and surface-enhanced Raman scattering (SERS) have attracted the attention of researchers due to the great potential applications in various research fields, including biomolecular sensing, analytical chemistry, surface science and material science. In order to improve the enhancement effect of the SERS substrate, the electric field enhancement of rice-shaped silver monomer, dimer, and trimer nanoparticles was simulated by the finite difference time domain method under different polarzation directions. The influence of the shape and spacing of the nanoparticles on local elecric field intensity were also studied and analyzed. On the above basis, the causes of electirc field enhancement were discussed in detail. The result shows that the electric field distributions of rice-shaped silver nanoparticles are different by changing the shape and spacing of the nanoparticles, as well as the polarization direction. The tip of the rice-shaped silver nanoparticle with long axis 300 nm, minor axis 36 nm and spacing 2 nm can produce maximum electric field enhancement when the incident polarization direction is parallel to the long axis. Moreover, due to the strong coupling between the nanoparticles, there is an obvious enhancement effect in the case of top to top configuration, and the obtained SERS enhancement factor (EF) is up to 2.41011. The conclusion provides theoretical basis for the preparation of silver nanoparticles in the SERS experiments.
2017, 46(2): 222001.
doi: 10.3788/IRLA201746.0222001
To solve the problem that the obtained stimulated Brillouin scattering(SBS) threshold from the measurement of backscattered power and forward transmitted power was higher than its real value, a new method employing Brillouin scattering spectrum width for fiber SBS threshold determination was proposed. The principle of local optical heterodyne detection and the relationship of the Brillouin scattering spectrum width with the fiber input power were theoretically analyzed. Experimental setup for Brillouin scattering spectrum measurement based on local optical heterodyne detection was designed, and the SBS thresholds of two standard single-mode fibers with different length were measured at room temperature. The results show that the Brillouin scattering spectrum widths corresponding to the SBS thresholds of 48.8 km and 9.5 km long fibers obtained from the power information are all approximate to a constant value of 10 MHz, and the serious pump depletion effect has occurred. The SBS thresholds are 1.12 mW and 3.8 mW for 48.8 km and 9.5 km long fibers determined by using the characteristics of the linear decline of Brillouin scattering spectrum widths at low fiber input power and the power independence of spectrum widths at high input power presenting in the Brillouin scattering spectra. The corresponding Brillouin spectrum widths are 24.86 MHz and 23 MHz, respectively, which are approximately equal to the natural Brillouin linewidth. The results of this study can provide a theoretical basis for the determination of the maximum fiber input power in Brillouin optical time domain reflectometer system.
2017, 46(2): 217001.
doi: 10.3788/IRLA201746.0217001
Two beams in the traveling the same path with opposite directions makes it is more suitable for stability beam combination. As a passive and separation device, spiral phase plate has the advantages of high efficiency and low working conditions. It has important significance to propose a method to generation vector beam with Sagnac interferometer and spiral phase plate combination. By analyzing the evolution of the orbital angular momentum states and the polarization states of the beams in the Sagnac interferometer, an isosceles right triangle optical structure beam combination system was designed. Without half wave plate, the optical structure was more compact and stability. The order of generated vector beams were checked with rotation of polarizer. The experimental results confirm the high stability and high efficiency of the combined beam method.
2017, 46(2): 217002.
doi: 10.3788/IRLA201746.0217002
Thirty meter telescope tertiary mirror is one of the largest flat mirror in this word. It is also called giant steering science mirror(GSSM). In order to better analyze and constrain the jitter of GSSM, the measurement procedure shall be carefully processed. The analysis and understanding of jitter testing was necessary, for the unique and tight requirements of jitter testing. The first section was about jitter testing with high accuracy encoder. And the error was simulated by Monte Carlo method for the profile and relative location between the tracker and the GSSM was discussed. The tilt axis location error for the co-axis case was 1 m versus the off-axis case 3 m. When it came to the rotational axis, the location error was 4.6 m, and the next consideration was the accelerometers used in the jitter test. For 333B32, at 2 048 Hz sampling frequency, the error was 0.6 m above 0.05 Hz. The jitter measurement provides useful insight for the jitter of the system, the error analysis consequently specifies the statistic property of the jitter. This will also give guide to the system engineering.
2017, 46(2): 217003.
doi: 10.3788/IRLA201746.0217003
In order to solve the problem of tracking fast moving targets, the control technique based on active disturbance-rejection controller (ADRC) of photoelectric tracking was studied. A third-order nonlinear expansion observer was designed based on the speed closed-loop transfer function to achieve a compensation of uncertainties, and the tracking error was improved by transforming the position transfer function. The performance of ADRC was demonstrated by numerical simulation and experiments. Compared with PI controller, the ADRC method shows better performance in the steady-state tracking error, the results indicate that the tracking error is improved by 7 times while the system tracks fast moving targets. Because of friction and noise, the tracking error is only improved by 4 times while the system tracks low moving targets; If phase compensation is introduced in control loops, the overshoot will decline by 40%, which shows higher practical value for the study of high-precision tracking control system.
2017, 46(2): 217004.
doi: 10.3788/IRLA201746.0217004
Centroid location accuracy of stars directly affects the limits of star sensor attitude measurement accuracy, one centroid location error is selection of spot model of star image energy in the algorithm. Star sensor's optical system inevitably has aberration which leads to changing of spot distribution, therefore, it has a realistic significance to explore the effect of optical aberrations on centroid location error for engineering application. Compared with the Gauss function model, four kinds of optical aberration were studied such as defocus and distribution law of centroid location error under the influence of the optical aberration. The analytical expression of location error was calculated combining with the physical process of centroid location, and its numerical simulation was achieved. Experimental results show that the different aberration result in respective spot distribution, further, different centroid location error. And the centroid location error will decrease if the edge energy gets lower evenly at a slow speed according to controlling aberration well. The analysis of centroid location error will help to guide the latter systematic error compensation, and principle of controlling optical aberration will guide the optical system design of star sensor.
2017, 46(2): 223001.
doi: 10.3788/IRLA201746.0223001
For the purpose of enhancing the stability and enlarging the dynamic range in trace gas sensing, the conventional wavelength modulation spectroscopy technology was improved by the introduction of logarithmic-transformed data processing method and differential detection circuit. Before the extraction of the gas absorption related harmonics using a lock-in amplifier, the logarithmic-transformation and the differential detection were fulfilled by a homemade receiver. Through the logarithmic-transformation, the optical intensity modulation of the laser emitting was separated from the absorption-induced power attenuation, and then the former was balanced during differential detection. Owing to this two-pronged strategy, each harmonic component of the absorption spectrum can be theoretically captured without the interferences of residual amplitude modulation and harmonic distortion. For the validation of theory, the second harmonic of P(6) absorption line for NH3 was acquired. The experimental temperature and total pressure were maintained at 296 K and 1.01105 Pa, respectively. Under the effective path length of 24.5 cm, a 0.7 ppm (part per million) detection limit was deduced on the assumption that the amplitude of signal was weakened to be equal with the noise. The above results indicate that this scheme is an ideal option for trace gas detection application.
2017, 46(2): 220001.
doi: 10.3788/IRLA201746.0220001
Photonic crystal fiber lasers have been paid much attention by many researches, and the preparation of photonic crystal fiber cores becomes the key problem in the study of the photonic crystal fibers. Er3+ doped aluminium-cadmium heavy-metal silicate glass sample was prepared by the method of high temperature melting. Its absorption and fluorescence spectra were measured. Using the Judd-Ofelt theory, its intensity parameter t (t=2,4,6), the oscillator strength and spontaneous radiation probability of the Er 3+ ion, fluorescence branching ratio, and the fluorescence lifetime were theoretically calculated. Using the fluorescence spectrum, the stimulated emission cross section of the 4I13/24I15/2 transition and the full width at half maximum(FWHM) of the fluorescence band were also measured. The result demonstrates that the Er3+ doped aluminium-cadmium heavy-metal silicate glass sample possesses a large stimulated emission cross section, a wide fluorescence FWHM, and high quantum efficiency of 92.6%. These parameters clearly indicate that this kind of silicate glass has a good laser excitation property and is expected to be applied in the study of the doped photonic crystal fibers.
2017, 46(2): 220002.
doi: 10.3788/IRLA201746.0220002
Light field imaging is an imaging method which can acquire the three-dimensional information of the scene. By inserting a microlens array between the main lens and the imaging sensor, it records both the radiance and the direction of the incident rays. Light field imaging using a gradient index liquid crystal microlens array (LCMLA) was proposed. Based on nematic liquid crystal materials for their anisotropy and birefringence, the LCMLA with a pattern of a circular-hole array was fabricated using ultraviolet lithography and wet etching. When an alternate voltage signal was applied between the two electrodes of the LCMLA, each microlens can converge incident rays effectively. An experimental system was set up to verify its focusing performance and measure its focal length. Then the LCMLA was assembled with a main lens and an imaging sensor to construct a light field imaging camera. Raw images were taken using the camera based on LCMLA.
