2014 Vol. 35, No. 5

OE System and Engineering
Testing method for frequency-domain characteristics of video processing system of EO tracker
Lu Pei-guo, Liu Xiao-qiang, Yang Xiu-lin, Shou Shao-jun, Wang Hu, Liang Xiao-dong
2014, 35(5): 739-743.
The EO tracker servo system design focuses on the frequency-domain characteristic parameters of the video processing system.We analyzed the theoretical model of the video processing system in the frequency domain, and designed a novel testing method. By using the velocity loop of the optical tracker servo system,through the frequency sweep in frequency domain and the contrast of the signal phases as well as the amplitudes,we indirectly measured the time lag and bandwidth of the video processing system. Taking a 50 Hz video processing system for instance,the tested bandwidth is 19.452 Hz, the time lag is 40.57 ms.
Indoor test model for photoelectric theodolite operating range
Wang Su-hua, Shen Xiang-heng, Ye Lu
2014, 35(5): 744-749.
Aiming at the operating distance of photoelectric theodolite indoor detection, we proposed an indoor model for testing the photoelectric theodolite range index. Starting from 4 boundary points in practical work process of the target tracking, we detected the photoelectric theodolite target contrast index, then estimated the working range by taking into account the weather conditions. The experimental results show that the photoelectric theodolite target contrast range is 5%~13%; On the condition of 45N, July, a no rain and no clouds day, the operating range is 30.105 km, and compared with the actual field flying result the error is about 1 km. This method is suitable for estimating the effect distance when tracking the targets under sky background.
Design of collaborative target tracking system using digital micro-mirror device
Zhu Han, Zhang Zi-li, Tang Ya-jun, Guo Xi-qing, Zhou Wei-hu
2014, 35(5): 750-755.
Aiming at the situation that the multi-lens target tracking systems have poor collaboration and the single-lens systems have narrow tracking view field which cannot realize wide field tracking, a coordination tracking system which can track target in wide field and observe local target simultaneously was designed. The system, based on the performance of high reflectivity and field segmentation of digital micro-mirror device (DMD), has good practicability, great realtime performance and simple structure etc. In validation experiments, the width field segmentation system realizes 50ms synergistic imaging cycle, and the less than 2% absolute position error of narrow filed image center adjustment system can make contributions to the solution of overlap problem between local targets beam center and narrow filed imaging system-s axis.
Method for enhancing distance in photoelectronic imaging under water
Zhang Ping, Qiu Wei-gen, Liu Xiao-dong, Zhang Bu-sheng, Sun Jian-hua
2014, 35(5): 756-760.
In order to increase the detection distance of the photoelectronic imaging underwater system and decrease its cost, the existing problem in the rangegated technology was analyzed and studied. A novel method for decreasing single pulse energy, enhancing system frequency and lengthening exposure time of charge coupled device (CCD) was proposed. Due to the random feature of the noise and relevance feature of the objective reflencetance, the mutiplue frame accumulation could enhance the maximum distance. The range-gated system was improved by such method, which was checked in the indoor water channel by the experiment. The experimental results show that this method can increase the detection distance effectively, and there is an optimum relation between the image quality and laser pulse numbers which is obtained by 10 pulses at the 29 m distance.
Design for scheme of infrared dual-band target simulator and projection optical system
Qian Yu-long, Hou Qing-yu, Wang Zhi-le, Zhao Huan-yi
2014, 35(5): 761-765.
Through the analysis of the traditional dual-band target simulator, a target simulator using only one generator and one projection system was put up to solve the problem of high cost and relatively complex structure. Using the method of division of amplitude, by the filtration of the filter and shading sheet, the energy of the two bands could transmit according to a specific proportion ,and in the specific integral time, detector could detect different energy ratios of the two bands, which could be used to simulate different infrared targets.Futhermore, the optic design of the projection system in the scheme was conducted.The projection system uses transimission model,which works in 3.3 m~3.8 m/4.4 m~4.8 m with a half field of view of 2.2 and an F number of 3.2 ,the system resolution could reach 10 lp/mm. The improved simulator can simulate the infrared objects of black body ,gray body,even selective body (300 K~3 000 K),with the radiation energy larger than the detected minimum energy ,proving scheme feasible .
Miniature design of large relative aperture MWIR zoom lens
Fu Wei, Pan Guo-qing, Yin Na, Sun Jin-xia
2014, 35(5): 766-770.
Optical system with a large relative aperture has a larger entrance pupil than its counterparts when their focal lengths are equal,so more energy collected and further distance detected. But due to its large aperture, the aberrations increase, which requires more lenses to correct and consequently cause application restrictions by volume and weight. To tackle this issue, zoom parameters were calculated and optimized reasonably, moreover by adopting compounded aspheric and diffractive surfaces, a reimaging zoom midwave infrade (MWIR) system with only 8 lenses was designed. The F number is 1.8 and the spectrum is 3 m~5 m. For a 320240 pixels detector with cooled focal plane array(FPA), the magnification is 5,and the four fields of view (FOVs) are 30 mm/60 mm/90 mm/150 m. The optical aperture stop matches the detector-s and the cold stop efficiency is equal to 100%. Two reflective mirrors are applied to fold the optical path, giving a compact volume of around 210 mm100 mm85 mm. Less lenses and simple zoom machinery effectively reduce the weight.
Design and analysis on large area uniform illumination with fly-eye lens
Wang Pei-pei, Yang Xi-bin, Zhu Jian-feng, Xiong Da-xi
2014, 35(5): 771-778.
A design with two parallel fly-eye lens arrays was proposed, in order to achieve a uniform rectangular light spot of large area. TracePro simulation was used to analyze the impact of the parameters, such as the space between two fly-eye lens and the back working distance of the optical system, on the size and uniformity of the light spot. The simulations indicates that the smaller the distance between the two lens and the longer the working distance, the larger the formed spot size. The best uniformity of light spot is obtained when the space between the two fly-eye lens is close to the focal length of the first lens. In one design, a spot with size 350 mm200 mm was obtained on the target plane, which was 1m away from the light source. In the central region of the spot, a range of 280 mm160 mm, which covered more than 60% of the total area, produced a light illumination uniformity higher than 85%. This design is expected to be used in medical phototherapy, street lighting, and many other fields.
Objective design of dual-waveband endoscope with image fiber bundles
Tong Jian, Xiang Yang, Dong Meng, Li Qi
2014, 35(5): 779-784.
In order to meet the needs for circadian reconnaissance and target detection, a visible and near-infrared dual-waveband endoscope with image fiber bundles was designed . After analyzing basic principles, the telecentric optical system in image space with retrofocus type was selected as its initial structure. Through the optimization with ZEMAX, the results of wavelength, focal length, F number,field of view (FOV) and optical length were respectively 0.486 m~0.656 m/0.7 m~1.1 m,1.21 mm/1.22 mm,4, 80 and 8.45 mm/8.47 mm.As the filament diameter of image fiber bundles was 16 m, and it was arrayed as square, the optical system needed to be evaluated at 31 lp/mm. The results show the requirement of telecentric path in image space is satified completely. It has uniform illumination at image plane on axis and off-axis. The modulation transfer function (MTF) value of this system is greater than 0.81 at the spatial frequency of 31 lp/mm in visible part, which is 0.80 in near-infrared part. The design of this dual spectral endoscope makes the function of traditional endoscope realized, and also enhances the range of detection and amounts of information, which can achieve the measurement and observation in day and night.
Grating optimization of long-wavelength QWIP based on surface plasmon
Wang Guo-dong, Ni Lu, Zhu Hong-wei, Wang Sai-li
2014, 35(5): 785-788.
In order to improve the sensitivity and detectivity of the long-wavelength quantum well infrared photodetector (QWIP) ,the surface plasmon was adopted to enhance the optical coupling efficience of two-dimensional grating .The modulation effects of the 2-D metal film grating parameters in long-wavelength QWIP on the incident light were analyzed by using the 3-D finite-difference time-domain (FDTD) algorithm based on surface plasmon. Calculation results shown that the electric field along the Z direction reaches its maximum in the X-Y plane when the grating parameters were taken as P=2.8 m , D=1.4 m and L=0.04 m for 8 m incident light.
Meter for luminous transmittance and haze of large transparent component
Wu Fu, Ren Jian-wei, Li Bao-yong, Wan Zhi, Liu Hong-xing, Liu Ze-xun
2014, 35(5): 789-793.
In order to obtain the luminous transmittance and haze of large transparent component in field, measurement scheme and method of calibration of system parameters based on double integrating spheres structure were presented. Furthermore the testing device was designed and manufactured. The optical path of device was adjusted by 6 dimensional mechanical adjustment structure firstly. Then the modulated directional light was generated by the illumination and collimation system based on LED source. Finally by using the detective part of double integrating spheres structure and the phase-locked amplifier technology, the signal was demodulated accordingly. The testing result shows that, by using the device, the absolute error of light transmittance is no more than 1% and that of haze is no more than 0.3%, which meet the precision requirement of engineering application. Moreover the repeatability of device was also good. The relative standard deviation of luminous transmittance and haze was 0.06 % and 0.05% respectively.
Optical system design of autocollimation
Zhou Dan, Xiang Yang, Gao Jian
2014, 35(5): 794-798.
An novel high-precision intellectualized electronic digital display autocollimator for two-dimensional photometry was designed, which could be used to measure small angles.The wavelength of the system was 670 nm.The foldback system was adopted in order to reach 1 m focal length and reduce the volume of the system.The position sensitive detector (PSD) was used as the optical receiver so that the accuracy of the instrument was increased and could meet the requirements that the measurement range was 6 and the accuracy was 0.1. The optical path system of the autocollimator was designed and optimized by Zemax.The emergent rays were parallel and the rays received by the determinand were homogeneous as shown in footprint diagram.These results can meet the needs of practical manufacture well.
OE Information Acquisition and
Large-scale image hierarchical grouping algorithm based on bag-of-words
Qian Jun, Yang Heng, Liu Pei-zhen, Jiang Wen-tao, Zhou Feng-fei
2014, 35(5): 799-805.
Automatical grouping algorithm on large-scale image set ,which is an important part of the scene reconstruction system, can help users organize the image set contents quickly. A hierarchical image grouping algorithm based on bag-of-words(BOW) was proposed. Firstly, each image is projected to a superhigh dimensional visual word vector by a multiple paths quantization (MPQ) method, and this step is so-called coarse grouping. Then, feature matching is carried out in every divided group and an affine invariant constraint is proposed to get rid of the incorrect matching features. This step is so-called refined grouping which can improve image grouping accuracy. The precision-recall curves show that the refined grouping can obviously improve the accucy of coase grouping ,and better grouping accucy can be achieved when using constraints.
Pyroelectric IRFPA mosaic image acquisition system with multi channels
Cheng Yao
2014, 35(5): 806-810.
In order to achieve large-scale pyroelectric infrared focal plane array (IRFPA) detector with high resolution, the readout circuit with multi-channel parallel output was designed. Based on the pyroelectric IRFPA detector of multiple-output and the pyroelectric detecting timing requirements, the system of mosaic imaging acquisition was designed. The external driving signals were used to control the trigger and sampling clock of acquisition card, and a chopper synchronizing signal was used to judge the bright field and dark field signal of the pyroelectric detector. The system was constructed with PC-DAQ virtual instrument system to acquire multi-channel parallel image, judge the bright and dark field for differential processing on each channel, and display a whole image after mosaic processing on software platform. The experimental image acquisition of the pyroelectric readout circuit with 160 120 two-channels readout and 320 120 four-channels readout were taken and the output signal waveform and image were showed after connecting the two-channels and four-channels signals. Compared with the single channel readout structure of the same scale detector, the readout speed of two channels structure doubles, and the four channels readout speed improves 3 times.
3D-object reconstruction based on fusion of depth images by Kinect sensor
Guo Lian-peng, Chen Xiang-ning, Liu Bin, Liu Tian-jian
2014, 35(5): 811-816.
3D reconstruction of object is an interest subject in computer vision. A method for 3D reconstruction of object was proposed by integrating a set of depth maps obtained by Kinect sensor. To aggregate the contributions of the depth images at their corresponding scale, the depth images were triangulated in image space firstly, and the next step was to insert the triangulated depth images into the hierarchical signed distance field, then the global Delaunay tetrahedralization was applied to all the voxel positions yielding a convex hull that covers all the voxels, and the marching tetrahedra algorithm was applied to the resulting tetrahedral mesh for extracting the surface. Experimental results show that this method can make use of 37 depth images by Kinect sensor at different directions with the resolution of 640480 to extract high-quality surfaces, which only costs 48 s.
Threshold de-noising method for mixed noise based on improved median filter and lifting wavelet transform
Li Jin-lun, Cui Shao-hui, Wang Ming
2014, 35(5): 817-822.
Images taken actually always have low signal-noise ratio(SNR),large noise density and mixed noise,however, most existing algorithms can only remove a single noise. Aiming at the mixed noise containing impulse noise and Gaussian noise, an efficient algorithm for mixed noise removal in image was proposed, including space impulse noise removal and wavelet Gaussian noise removal. In the process of de-noising, an impulse noise detection algorithm based on median filter was given to filter impulse, and at the same time a lifting wavelet transform for image was applied to remove Gaussian noise. Simulation result shows when (,)=(0.4, 20), the peak SNR(PSNR) is 34.002 1 and the mean absolute error( MAE) is 2.365 3.
Wavefront detection technology based on Shark-Hartmann theory
Guo Guang-yan, Fan Zhong-wei, Yu Jin, Ge Wen-qi, Kang Zhi-jun, Tang Xiong-xin, Mo Ze-qiang, Wang Hao-cheng, Shi Zhao-hui
2014, 35(5): 823-829.
Precise wavefront detection is an important basis for reflection mirror figure test and wavefront distortion measurement. According to the theory of SharkHartmann, the wavefront detecting technique was studied by simulation and experiments. The spherical wave/cylindrical wave, formated by the parallel lights transmitting through the spherical lens/cylindrical lens, were detected as the wavefronts. In experiment the commercial microlens array and charge coupled device (CCD) were utilized to build the Shark-Hartmann sensor, and the actual light beam was used as a reference to avoid the influence of the optical alignment error on system. The simulated calculation results show that the mean curvature error is 13.423 mm, and the experimental results indicate that the spherical/cylindrical/tilt wave detection and recovery can be realized.
Optical Metrology and Measurement
Terrestrial calibration method of focal plane position of space CCD camera
Cao Zhi-rui, Dong Ji-hong
2014, 35(5): 830-834.
In order to calibrate the focal plane position of a space charge-coupled device (CCD) camera in terrestrial measurement stage, we proposed a novel calibration method based on the principle of autocollimation interferometry and modulation transfer function(MTF) measurement. We introduced the principle and the implementation process of the proposed method, and taking the calibration of focal plane position of a space CCD camera with a aperture of 600 mm and a focal length of 6 m by a collimator with a diameter of 1 m and a focal length of 20 m as an example, analyzed and calculated the calibration precision of the novel calibration method and the existed calibration method. The results show that the precision of the novel calibration method is better than 0.006 mm, which is 5 times~10 times of the existed calibration method, and this precision of the novel calibration method could meet the requirement on the calibration precision of the focal plane position of all the space CCD cameras at this stage.
Application of image measuring technology in blade tip clearance measurement
Zheng Chen, Zhu Mu-cheng
2014, 35(5): 835-840.
For the problem that it-s difficult to measure the blade tip clearance of turbine engines and its low accuracy, a high-precision measurement for blade tip clearance in the assembly process was proposed by utilizing image measurement, through using the defined calibration, an improved edge detection, the Hough transform and image super-resolution restoration technology, as well as operating the motion control mechanism, the industrial CCD camera and the open source computer vision library, an unique image measurement system was designed to achieve the high-accuracy and non-contact measurement of blade tip clearance. The experimental results show that the measurement accuracy reaches 15 m.Compared with other tip clearance measurement and image measurement system, this method not only improves accuracy, but also has a good portablility, low cost and stronger applicability.
Assembly and adjustment method based on aberrations correction for telescope optical system
Li Li, Li Gang, Xu Chun-mei, Shen Hong-bin, Wang Yuan-bo, Yin Jian-ling
2014, 35(5): 841-847.
In order to ensure the imaging quality of certain type telescope at assembly stage, an alignment method based on aberrations correction was proposed. The optical system model of this telescope was set up and the misalignment phenomena for every optical element was simulated to analyze the changes of aberrations, then the sensitivity matrix of optical element for aberrations was calculated and the best alignment scheme was determined to improve the assembly quality and efficiency.Finally the alignment experiment based on star test was conducted, the results show that the technique indicators are all satisfied after alignment and the resolution is better than required 7.5,which could validate the feasibility of our method and offer operability for the assembly and adjustment of this kind of instrument.
Crucial algorithms for structural light 3D measurement system calibration
Zhu Tong-jing, Zhou Ping, Liu Xin-ran, Yuan Jun-jie
2014, 35(5): 848-852.
System parameter calibration is crucial to structure light three-dimension measurement system. The calibration error is mainly due to the detection accuracy of the characteristic circular center of calibration board and the gamma distortion of the projector and camera. An accurate circular center detection method and a gamma pre-calibration method were proposed to improve calibration accuracy. The pixel edge detection with Sobel operator and subpixel edge detection with orthogonal Fourier-Mellin moments (OFMM) operator were used to detect the circular edge accurately, moreover, the circular center was detected by ellipse fitting method. The gamma nonlinear distortion model was analyzed to obtain the system gamma value, whose reciprocal was used to modify the ideal sinusoidal fringe pattern as its exponent. The experimental results show the effectiveness of the methods. The calibration accuracy increases by a factor of 3.5 in X direction and 5 in Y direction compared with that without these methods.
Influence of detection wavelength drift on visibility measurement
Xiao Shao-rong, Shang Guo-qing, Zhou Jia, Xu Meng, Wu Qun-yong
2014, 35(5): 853-857.
In order to study the influence of detection wavelength drift on visibility measurement,based on the definition of Koschmieder empirical formula and the aerosol transmittance of 400 nm~1 100 nm waveband measured in experiment, the influence of detection wavelength drift on visibility measurement was analyzed. The results show that the relative error of visibility measurement is related to detection wavelength, range of detection wavelength drift and aerosol extinction characteristics. The relative error of visibility measurement increases with the range of detection wavelength drift in linearity. With the increasing range of detection wavelength drift, the linearly increasing rate of the relative error in visibility measurement at each wavelength is different. Under the same range of detection wavelength drift, the visibility measurement error is different by using the different detection wavelengths. In a certain atmospheric environment, the relative error of visibility measurement caused by detection wavelength drift can be reduced obviously by using the light of a specific center wavelength with small drift as the detecting light.
Micro-vibration measuring technology based on heterodyne interference
Liu Dan, Zheng Bin, Guo Hua-ling, Liu Hui, Liu Nai-qiang
2014, 35(5): 858-861.
Aiming at the problem that the micro-vibration based on heterodyne interference has low stability and is easily impacted by environmental noise, the ideas of optical path improvement were given. According to the difference principle, the single optical path was converted to a double optical path, in which the environmental noise was eliminated; The elliptically polarized light was changed into linearly polarized light to improve the interference signal amplitude by the polarization splitting prism (PBS); The acoustooptic modulator(AOM) was improved to inhibit frequency drift;The stray light was suppressed by using diaphragm filters so as to improve the system signal-noise ratio (SNR). The verification experiments were conducted through detecting 5 kHz piezoelectric vibration signal and 2.5 MHz laser ultrasonic signal .Experimental results indicate that signal is stable and has no ripple,the resolution is 2.3 nm and the SNR has improved by 16.7 times. The amplitudes of double-channel heterodyne interferometer signal is 552 mV and 736 mV, respectively, which are larger than traditional one nearly 10 times, it is advantageous to measure nanometer micro-vibration signals.
Optical Element and Fabrication
Calculation of thermal deformation for auto guide telescope of NVST
Cheng Xiang-ming, Deng Lin-hua, Liu Guang-qian
2014, 35(5): 862-867.
The guide telescope ,as an integral part of the guide system of the 1m new vacuum solar telescope (NVST),its stability of imaging is essential. It is necessary to be concerned that the deformation of the telescope structure caused by environmental thermal load may cause thermal defocusing and affect the image quality of the guide telescope. The temperature distribution of guide telescope at -5 ℃, 20 ℃ and 35 ℃ were analyzed using finite element method, and then the axial deformation of guide telescope caused by temperature field was calculated. The maximum defocusing amount is 6.45 m, and the results show that the max change of distance between the primary mirror and the target surface is far less than the depth of focus(35 m) ,which provides a basis to analyze the non-thermal design of guide telescope of NVST.
Technique challenges in coupling of high resolution spectrograph with extremely large telescope
Zhang Chi, , Zhu Yong-tian, Zhang Kai
2014, 35(5): 868-872.
We reviewed the designing of several international ground-based extremely large optical/infrared telescopes and introduced the problems faced in the coupling of high resolution spectrograph with telescopes of extremely large aperture. It is proposed that large area of echelle and ultrafast focal ratio camera can serve as a solution. According to the coupling rule of the spectrogragh and the telescope, the diameter of collimated beam for a 30 m telescope would be over 70 cm, and the size of the main dispersion echelle grating would be larger than 2 m2. To build such huge and costly equipment would be difficult with current techniques. And large aperture camera with focal ratio F/0.5 is also hard to design and manufacture. Image slicer, mosaic gratings and white pupil optic become major solutions in designing the high resolution spectrograph for an extremely large aperture telescope.
Theoretical modeling and experimental study on optical fiber grating pressure sensor
Ran Xin-tao, Ma Shao-ping, Li Xi-liu, Xue Xiao-le
2014, 35(5): 873-879.
Pressure sensor is a key element for pressure supervising during industrial production. The mathematical relations between the central wavelength and the strain of optical fiber grating were analyzed. The mathematical relations between the deflection of central diaphragm and the pressure were analyzed when the circular flat diaphragm with rigid center was in uniform compression. A circular flat diaphragm was designed as the sensing element of fluid pressure and the converter to transfer the fluid pressure to optical fiber grating. The optical grating sensor was assembled with secondary element and the linear mathematical model of the input and output of the sensor was built. The linearity and repeatability of the sensor were demonstrated by experiments. The parameters of the optical fiber grating pressure sensor were got using mathematical computing. The sensitivity of the optical fiber grating pressure sensor is -0.658 nm/MPa, and the initial wavelength is 1 578.441 nm. This research paves the way for the further stability of the sensor.
Electro-optic characteristics of polymer dispersed liquid crystals doped with thulium oxide nanoparticles Nd2O3 in UV based on numerical fitting
Jin Xiang, Wu Hong-ye, Zhao Jian-jun, Lu Yi, Liu Gui-xiang
2014, 35(5): 880-883.
The new electro-optic properties of polymer dispersed liquid crystal (PDLC) have attracted considerable attention in recent years. The nonlinear numerical fitting was used to investigate the transmittance of PDLC doped with thulium oxide nanoparticles Nd2O3 (PDLC- Nd2O3). The experimental result is a sum of sinusoidal function in the given experimental condition, which is 20 V~30 V for driving voltage in 335 nm~375 nm. Fitting results show that the minimum correlation coefficient (R) is 0.999 8 and the maximum root-mean-square error (RMSE) is 0.057. Moreover, the nonlinear numerical fitting of the position and trend of the absorption band peak along with the driving voltage was done ,and two mathematical functions were achieved whose inter mathematical relationship is a quadratic polynomial. Fitting results show sum-square errors (SSEs) are 1.292e.026 and 3.944e.030 respectively, the correlation coefficient is 1. The results fit well with the experimental data, which could be used to further understand electro-optical properties of the PDLC- Nd2O3 in UV in 20 V~30 V driving voltage.
Infrared Technology
Infrared real-time calibration technology based on temperature control blackbody
Zhu Hui, Zhang Yong, Chen Zhi-xue, Dong Qi-lin, Liu Wan-gang, Luo Bei-bei
2014, 35(5): 884-890.
Non-uniformity correction (NUC) of 2nd generation scanning thermal imager usually utilizes the fixed two-point temperature calibration method or the fixed multi-point temperature calibration method. However, the fixed-point correction cannot adapt to the changes of the detectors caused by the environment or time, hence the calibration parameter is deviated and the space errors increase. We put forward a kind of real-time correction method by setting two controllable temperature blackbodies in the light path ,and the temperature of the blackbody always followed that of the scene in real time. So the correction parameter was updated in real time to effectively reduce the output error. With some contrast tests of the different scenes, results show that for the traditional fixed point correction, the size of the nonuniformity noise is about 4.0, while adopting the method of this paper, the size of the noise is not greater than 2, effectively reduces 50%.
Design of infrared methane gas concentration detection system
Zhu Hong-xiu, Sun Lian-kun, Wang Zhong-hua, Nie Zhe, Liu Huan
2014, 35(5): 890-894.
In order to accurately measure the volume of methane gas concentration, we adopted the parallel infrared illuminant, IRL715EN-PR, to design an infrared methane gas detection system . The whole detection system consisted of hardware circuit and software system. We put forward and implemented a new algorithm about signal processing. At the same time, a feeding dog in interrupt service routine (ISR)program was designed so as to greatly extend the watchdog timer reset time. Using Matlab for data fitting, we achieved a function of concentration and voltage of the system. Experiments show that the volume concentration is in the range from 0% to 4%, the greatest relative error of the system is less than 1%.
Laser Technology
Optimization of pump structure parameters in LDA side-pumped solid state laser
Han Yao-feng, Zhang Ruo-fan, Liu Guo-rong, Yang Hong-ru, Li Jun-fang, Liu Fang, Li Yong-feng, Liu Xiaoying
2014, 35(5): 895-901.
The numerical model for pump light distribution of laser diode array( LDA) side-pumped laser rod was set up, the characteristics of pump light distribution in crystal of Nd∶YAG were analyzed in detail based on that model.The analysis results could be theoretical guidance for optimization in LDA side-pumped solid state laser designing, optimization and experiment. Several parameters which may influence the pump light distribution were discussed, such as the distance between bars, the thickness of glass tube and the radius of laser rod. Based on these numerical analyses, the pump parameters of LDA sidepumped solid state laser were optimized.The optimized analyzing results show that while the rod diameter is 4 mm,the bar distance is 0.4 mm,the glass tube thickness is 1 mm and the water thickness is 1 mm under the circumstance of 2 mm pump distance, we could obtain that the relative pump intensity in the center of the crystal is 40.8%,and the distribution near the axis of crystal is a relatively large homogeneous area.
Laser conditioning effect of HfO2/SiO2 film
Li Hai-bo, Du Ya-wei, Zhang Qing-hua, Wei Yao-wei
2014, 35(5): 902-907.
Large aperture laser was used to irradiated the HfO2/SiO2 reflectors, which were evaporated from hafnia and silica by e-beam. Laser calorimeter was used to test the film absorption before and after laser irradiation. The results show that film absorption decreased from 5.4%, 1.7% to 1.4%, 1.2%, when the measurement wavelengths were 1 064 and 532 nm, respectively. Focused ion beam (FIB) was used to study the damage morphology after laser irradiation and to explore the cause of damage. The film where nodule existed was easily damaged, and the damage morphology mainly presented melt, partly erupted and absolutely fallen off. For the HfO2/SiO2 reflectors, laser conditioning was effective to eject the nodules on substrate. It was result from the nodule residue not to affect the subsequent laser. In addition, laser conditioning was not effective to the nodule in the film, which may be from the material spatter in coating process. In this case, other method can be used to get rid of the nodules.
Design and simulation of axial super-resolved phase plate in femtosecond laser microfabrication
Cai Jianwen
2014, 35(5): 908-911.
In order to improve the quality of laser micromachining, the focal spot should be shaped. The Fresnel diffraction formula was analyzed, two kinds of axial super-resolved phase plates were designed by using Matlab based on genetic algorithms and design constraints. The normalized radiuses of 0. structure phase plate of four-ring are r1=0.15、r2=0.70、r3=0.81, and the normalized radiuses of non.0. structure phase plate of four-ring are r1=0.25、r2= 0.498、r3=0.652, the phases of each ring from the inside to the outside are 2.879、3.087、0、3.012. The longitudinal spot sizes after using the two phase plates are compressible to 76% and 75% of the Airy pattern , the ratios of the peak energy are respectively 0.39 and 0.42, and sidelobe energy are respectively 0.64 and 0.41.Two phase plates can be applied in femtosecond laser microfabrication.
Temperature field analysis of single-layer HfO2 film induced by long-pulse laser
Li Hong-jing
2014, 35(5): 912-916.
Optical coatings in a laser system are easily damaged, so it is important to investigate the temperature field of the film irradiated by a long-pulse laser. A spatial axisymmetric finite element model of single layer HfO2 film with a high-absorptance platinum inclusion was used to study the thermal damage induced by a long-pulse laser. Influences on the temperatures of the film and substrate by the absorption coefficient and the depth of the platinum inclusion in the film were analyzed. The results show that the maximum temperature in film surface, compared with pure HfO2 film, can be increased more than one time when the depth of inclusion is 100nm; when the depth of inclusion reaches 750 nm, the temperature of substrate is higher than that of film, which may cause first damage of the substrate. Results of the research can provide a reference for optical film design in the preparation and preprocessing of thin film applied in the long-pulse system.
Influence of flame atomic absorption on measurement of K using laser-induced breakdown spectroscopy
Zhang Zhi-hao, Song Qiang, Yao Qiang
2014, 35(5): 917-921.
When the measurement of alkali metals is performed using laserinduced breakdown spectroscopy (LIBS) in flame,the emission of the alkali atoms in the plasma can be absorbed by the alkali atoms outside the plasma in the flame,influencing the LIBS measurement accuracy. Based on the BeerLambert law and the thermodynamic equilibrium calculation,a flame atomic absorption model covering the concentration range of K released during practical biomass combustion was developed,and the influences of the atmosphere of the flame,the K distribution and the total K concentration on the flame atomic absorption efficiency were analyzed. It is found that,with the increase of the O2/CH4 ratio,the equilibrium molar fraction of atomic K in all Kcontaining species decreases from approximate 25%,leading to the decrease of the flame atomic absorption efficiency from 86.8%. When the O2/CH4 molar ratio ratio exceeds 2,excess O2 exists in the flame, and the flame atomic absorption efficiency is always less than 13%. Meanwhile,by proper adjustment of K distribution and the total K concentration,the flame atomic absorption efficiency can also be reduced. Based on this,it is proposed that to reduce the flame atomic absorption efficiency and facilitate the K LIBS measurement accuracy in flame,an oxidizing flame atmosphere and a proper K distribution profile should be created.
Influence of materials-properties of targets on laser voice detection
Zhang Yu-ze, Li Li-yan, Zeng Hua-lin, Zhou Yan
2014, 35(5): 922-926.
To enlarge the application scenario of laser voice acquisition system and analyze the influence of targets- material properties on voice acquisition, based on the acquisition process of voice signal from sound source to target, we established a vibration model of targets based on Sewell-Sharp-Cremer model and proposed a calculation method for targets- vibration amplitude. Through Matlab simulation and experiment, the amplitude and voice acquisition results of Fe, Al, plastic and paper were compared. The results show that the amplitudes of 4 targets decay exponentially during 300 Hz~1 000 Hz and go flat above 1 000 Hz. Vibration amplitudes of non-metallic materials are 69nm and 62 nm while those of metal materils are 30 nm and 10 nm. Therefore, metal materials are more appropriate to be the target for voice detection according to their small dynamic range and low frequency sensitivity.