2009 Vol. 30, No. 2

OE System and Engineering
Adaptive window object tracking based on variable resolution
LI Liang-fu, FENG Zu-ren, CHEN Wei, BAI Bo, CHEN Wei-dong, JI Ming
2009, 30(2): 177-182.
This paper presents an adaptive window object tracking method based on variable resolution. It copes with size changing object during visual tracking. For the visual tracking algorithm based on maximum posterior probability, we analyze the posterior probability contribution on the inside and outside panes of the object window, and build a mathematical model for adjusting object size with an adaptive window. Since the resolution changes according to the size of the object, this thesis uses a statistical sampling method of the feature by variable resolution. The resolution of the statistical feature is correspondingly changed in object tracking with an adaptive window. The resolution of a larger object is decreased, which realizes an object tracking method with adaptive window based on variable resolution.
Optical image encryption based on frequency splitting domain and Fresnel domain
REN Guo-zhao, JING Xi-li, XIE Dan-yan
2009, 30(2): 183-186.
A method of the optical image encryption based on the frequency splitting domain and Fresnel domain is proposed, after the analysis of the fractional Fourier transform and Fresnel transform, by synthesizing the advantages of multi keys and lensless feature of the fractional Fourier transform and Fresnel transform in the optical image encryption system. The Fresnel transform and hologram technique are introduced into the optical encryption system with the fractional Fourier transform to improve the security of the original encryption system without increasing other optical elements. The theoretical analysis and computer simulation indicate that the method is feasible.
Thinking on key technology of vehicle mounted extensible mast system
CHEN Li-xue, LIU Yu, LI Rui-feng
2009, 30(2): 187-190.
For enhancing the operating range of vehicle mounted E-O system and keeping better observing ability when the vehicle is concealable, an elevator mast system which could burden a long-range E-O system was designed. The compound transmission mode which combines the hydrolic drive with the mechanical transmission assembly is adopted. The square structure is used by the mast, whose length-width ratio is controlled within 1∶20. It is made of aluminium alloy, and its well thickness is more than 3mm. Its raising height is 10m, the duration of rising up or getting down is 1min, and the maximum loading capacity is 200kg. The loading capability, wind resistance and vibration characteristic of the mast are analyzed. A spring take-up without slip ring is presented, which is suitable for the signals to go to or come from the mast and the current to reach to the optical systems mounted on the top of the mast.
Distribution characteristics of LED arrays based on MATLAB
HUO Yan-ming, WU Shu-mei, TAN Jun-ting, FENG Li-hua
2009, 30(2): 191-194.
As the power of a single LED is very small, when it is taken as the illuminating source, it is necessary to use LED array to enhance the brightness and enlarge the luminous area to improve the uniformity of illuminance. The luminous superposition formula of the LED array is derived, and then the LED array is simulated according to the formula. The uniform distribution of LEDs on a plane is analyzed taking the circular distribution as an example and the homogeneous distribution of LEDs on a curved surface is analyzed taking the spherical distribution. The simulation results of two kinds of arrays' characteristics are presented. The distribution features of different arrays were obtained. The array distributions applied to different lamps are achieved and reliable reference for the design of LED lamps is provided.
Fast template matching tracking algorithm based on image separation block processing
QIANG Shi-jin, RONG Jian
2009, 30(2): 195-198.
The application scope of traditional template matching tracking algorithm is limited because of its large computation load and poor real-time performance. In order to overcome this problem, it shall be optimized to meet the real-time requirement. A modified real-time imaging tracking algorithm based on the available position prediction relevant tracking algorithm is presented by utilizing the image block processing to decrease the calculation load of traditional correlation tracking algorithm and improve the real-time performance. The modified algorithm was simulated and verified in the experiment. The result of simulation indicates that the presented algorithm decreases the matching calculation load and improves real-time performance, reduces the effect of the stochastic noise and makes tracking faster and accurate.
Design of wide spectrum low-light-level collimating lens
GUO Cheng, WANG Gao-ming, ZHANG Liang-liang, YANG Zhi-wen
2009, 30(2): 199-201.
The optical design of wide spectrum WFOV LLL collimating lens and the structure of lens set are introduced. The correction of the secondary spectrum of the WFOV LLL collimating lens are described emphatically. According to the primary aberration theory, the initial structure parameters of the system were solved. A design of a lens, whose operating wavelength is (0.486~0.863)μm, full field-of-view angle is and relative aperture is 1∶7.85, is presented on the basis of the theoretical calculation and the optimization of optical design software ZEMAX. The MTF of the lens, which is composed of five spherical lenses and one asphere lens, is better than 0.8 at the spatial frequency of 20lp/mm. The design makes the secondary spectrum of the lens to be at 0.01mm and other aberrations also met the requirement of the application.
Optical characteristics of black carbon and dust aerosols with HITRAN data
GE Jin-ming, LIU Yu-zhi, HUANG Jian-ping, SU Jing, LI Ji-ming, BI Jian-rong
2009, 30(2): 202-209.
The numerical algorithm of Mie theory was realized in IDL. The scattering efficiency and phase matrix elements of black carbon and dust aerosols at 400nm and 860nm wavelength were calculated when their radius were 1m,2.5m and 10m. The results show that the optical characteristics of the black carbon and dust are significantly different, and both the scattering efficiency and backward scattering of the dust are greater than those of the black carbon. Since the lighting polarizations of the two aerosols are different at the sun light of 400nm and 860nm, both the aerosols can be distinguished with the characteristics.
Realization of all-optical interconnection based on optical solitons′ interaction in strong nonlocal medium
ZHANG Xia-ping, LIU You-wen
2009, 30(2): 210-214.
Ion beam neutralization of broad beam cold cathode ion source
MI Qian, GU Ke-yi, QIN Ying
2009, 30(2): 215-219.
Charge accumulation effect on the surface of the insulation film degrades the quality of the films in the process of IBAD. A square wave AC voltage power is connected to the extraction grid of the broad beam cold cathode ion source. Therefore, the positive and negative charges are neutralized to eliminate the discharge phenomenon on the surface of the film by extracting the electrons and ions out. The parameters, such as the initial energy, densities and radiation angle of the electron beam were tested in the experiment. The experiment results show that the average electronic energy is about 100eV and the emission angle of the extracted electron beam reaches ±40° when the extraction voltage is 600V. With the same parameters, the beam flux of the extracted electron beam is less then the ion beam. A good neutralization effect can be obtained by adjusting the duty cycle of the pulse power.
Energy transfer of OLEDs made from PVK doped with fac-tris-2-phenylpyridine iridium (III)
YANG Shao-peng, ZHAO Fang-chao, QIU Xiao-li, QIN Xiang-dong, WANG Li-shun, JU Xiu-qin
2009, 30(2): 220-224.
The phosphorescent electroluminescent devices were developed by doping different proportions of fac-tris-2-phenylpyridine iridium (III) (Ir(ppy)3) into PVK as a light-emitting layer. Through the research of the luminescence mechanism, it is found that in the process of photoluminescence (PL), Fo¨ster energy transfer mechanism plays a dominant role, and in the process of electroluminescence (EL), the two types of energy transfers as Dexter energy transfer and charge trapping affect the luminescence performance. The I-V-L characteristic of the device shows that the lightpower efficiency is highest and the energy transfer is the most efficient when the doping proportion of Ir(ppy)3 is 5%.
Special functions for beam drift in atmospheric turbulence
GAO Ming, LI Zhan-bin
2009, 30(2): 225-228.
In order to improve the sighting accuracy of a tracking and sighting system, the application of special functions in laser beam drift occurred in atmospheric turbulence was studied. Based on special functions and modified Von Karman spectrum, some expressions are derived for the variance of the beam drift in the slant path. Numerical simulation shows that neglecting the higher-order terms of the special function will not significantly reduce the laser beam pointing accuracy for a long-distance transmission. When the outer scale of turbulence L0 is rather small, the outer scale of the turbulence has great effect on beam wander. When L0 increases, the variance of the beam wander will increase slowly and approach saturation. In the same outer scale of turbulence, the increase in transmitting aperture (original beam width)and transmitting zenith angle will prevents beam from drifting. Especially, the variance of the beam drift decreases rapidly when zenith angle is close to π/2. Numerical simulation shows the above results are useful for improving the accuracy of the tracking and sighting system.
OE Information Acquisition and Processing
High precision lens jacket method based on image processing
FU Wen-qing, XU Feng, WANG Yong-liang
2009, 30(2): 229-232.
A method of lens jacket based on image processing is presented, which can reduce the eccentricity of lens effectively. Based on the features of the lens to be jacketed, the parameters of the optical path are calculated. An area array CMOS device is used to get the reflected cross image from the lens. By using image processing methods to get the eccentricity value, the position of the lens is adjusted to reach the tolerance and the jacket is machined. The testing setup, the motor control system and the software are described. The experiment result shows the method is effective in reducing eccentric error.
Study on pre-processing of THz laser active image
YAO Rui, LI Qi, YIN Qi-guo, WANG Qi
2009, 30(2): 233-235.
THz laser active imaging is a kind of new imaging system. It has great potentials in hazardous material detection, medical care and food inspection because of its low photon energy (about 4.1meV per THz) and high penetration capability. In this paper, the contrast stretching transformation, median filtering and mean filtering are applied to pre-process the THz array image of a 5RMB watermark. The processing results show that these imaging processing methods could be introduced to the preprocessing of THz laser active image and satisfactory results are obtained.
Laser detection of ship wake flow based on phase-locking amplifier
LIU Chang, JI Bang-jie, LI Jian-chen, WANG Hai-lu, YAN You-rong
2009, 30(2): 236-241.
There are many micro-bubbles in the zone of ship wake, which makes it different from the normal sea water. A method to detect the signal of ship wake by two-path phase-locking amplification technology is proposed based on the ship wake optical characteristics. Lock-in amplifiers are good at weak signal detection and they are used widely in many areas. By using orthogonal lock-in amplifier technology to eliminate the laser drift of the laser detection system in the process of the ship wake detection, it can reduce the noise and make the detection system more sensitive and reliable.
Adaptive SMC for nonlinear optoelectronic servo ystem with uncertainty
WANG Hong-hong, CHEN Fang-bin, JIANG Tao, LI Guang-liang
2009, 30(2): 242-245.
An improved exponential approach method and the system parameter online estimation based on the adaptive theory were implemented in a nonlinear optoelectronic servo system with parameter and structure uncertainties. SMC is applied to the design of APR in the system. Taking the equivalent 1.2sin(0.93t) as the simulation input, the tracking error is less than 60 μrad after 0.45s. The simulation indicates the control method for such uncertain nonlinear system is effective.
Stray light analysis of Fabry-Perot interference imaging spectrometer
DU Shu-song, WANG Yong-mei, DU Guo-jun, WANG Ying-jian
2009, 30(2): 246-251.
Proceeding from the definition of the stray light, the source of the stray light was analyzed since the stray light affects the image quality of optical systems seriously. The leading indicator adopted to assess the effect of the stray light on the optical systems, and the mathematic model of point source transmittance and stray radiation ratio were established. The stray light of a Fabry-Perot interference imaging spectrometer was analyzed and calculated with TracePro. It is found that the stray light in optical systems can be effectively restrained and the stray radiation ratio can be effectively reduced by adding a diaphragm in the systems. The optical and mechanical system design of Fabry-Perot interference imaging spectrometer was performed by the aid of the analysis result to eliminate the stray light.
Recognition algorithm for star pattern of little swatch based on BP neural network
MA Tao, SUN Hong-hui, XIAO Song, LIU Chao-shan
2009, 30(2): 252-256.
BP neural network is used to improve real-time and robustness for star pattern recognition algorithm of star sensor. According to the trajectory, the navigation stars and corresponding pattern were reduced, that is, the star chart in FOV (field of view) corresponds to one and only navigation pattern. The largest empty circle on plane is computed to construct the exhaustive set in FOV by two-dimensional Voronoi diagram, and then the exhaustive set is constructed. By iterative comparisons, it is found that the navigation pattern of all the stars′ convex polygon in FOV can be composed if the fixed stars are chosen as the convexes, and taking its angle distance and vertex angle as the recognition vectors has the advantages of translation and rotational invariance. The simulation experiment shows that the success rate of accurate recognition is one hundred percent and the time of recognition is less than 20ms. Therefore, the recognition algorithm has a certain utility value.
Effect of amplitude proportion and phase difference on ropagation of optical soliton pair
MENG Xiao-bo, ZHOU Jun, GAO Yong-feng, REN Chun-yang
2009, 30(2): 263-267.
The optical soliton nonlinear Schrodinger (NLS) equations with three-order dispersion effect and without three-order dispersion effect were respectively resolved with the split-step Fourier transform method (SSFM). It is found by the numerical solution that the three-order dispersion effect may cause the soliton pair pulse to oscillate on a single side and may produce the sub pulse in the oscillating side; and also found that the phase difference and amplitude proportion play an important role when there is no effect of three-order dispersion, but only phase difference results in the obvious influence on the propagation of soliton pair while there is the three-order dispersion effect, and it can make energy transfer. The effect of amplitude proportion and the phase difference between two soliton pulses on the propagation of soliton pair is discussed.
Optical Metrology and Measurement
Method of reconstruction on Fourier-Transform spectroscopy
LI Su-ning, ZHU Ri-hong, LI Jian-xin, WANG Yan
2009, 30(2): 268-272.
In the course of spectrum reconstruction of Fourier-Transform spectrometer, there will be large error of the spectrum if the interferogram is transformed directly without any other process, because there is machining error as well as some other errors in the system. According to the theory of Sagnac FourierTransform spectrometer, the method which we used to reconstruct the spectrum correctly from the captured interferogram was developed. With the steps of trend term correction, apodisation, phase correction and conjugate symmetrization applied to the interferogram captured and then reconstructed it, the error was avoid.The experiment to reconstruct the spectrum of monochromatic light source such as Helium lamp used in the developed prototype was carried out. The results agree with the nominal spectrum distibutions of the sources with the accuracy of 4nm.
Testing of large aspheric surfaces by subaperture stitching interferometry
2009, 30(2): 273-278.
In order to test large aspheric surfaces without the aid of null optics, the subaperture stitching interferometry (SSI) was proposed. The theory and principle of the technique were analyzed, the optimized stitching model and effective stitching algorithm were established based on homogeneous coordinates transformation, simultaneous least-squares method and Zernike polynomials fitting. The software of SSI was designed, and the computer simulation was carried out, the prototype for testing of large asphere by SSI was designed and developed. The experiment was conducted with five subapertures for a 350mm hyperboloid. For comparison and validation, the asphere was tested by null compensation as well, the synthesized surface map is consistent with the entire surface map from the null test; and the difference of PV and RMS error between them was 0.032 and 0.004(=632.8nm), respectively.
Comparison method for CCD camera accuracy in photography measurement
ZHANG De-hai, LIANG Jin, GUO Cheng
2009, 30(2): 279-284.
Digital photography measurement is widely used in the fields of reverse engineering and 3D inspection. CCD camera measurement accuracy in the photography measurement is discussed. A calculation method based on the mathematical statistics is put forward. The distance of coded points or uncoded points was calculated with several groups of photographs taken by a camera with software XJTUDP, and then their average value was acquired. The individual error of each measurement was obtained by subtraction of the average value from the measured individual value of each group. The measuring accuracy of every group and the concept of standard accuracy were acquired by deriving the absolute value of ratio between the individual error and average value. The standard accuracy can be taken as the criteria for judging the accuracy of CCD cameras. The Cannon400D fixedfocus camera and zoom camera were analyzed in combination with the method and experiment data. The scientific basis for selection of zoom cameras and fixed-focus camera was provided.
Simulation and analysis of thermospheric wind velocity
LI Hao, ZHANG Yan-ge
2009, 30(2): 285-290.
Interferometer can be used in the measurement of thermospheric wind velocities and there are strict requirements on the measurement system since the intensity of source (emission of airglow) is very weak. Based on the modulation property of a laser diode (LD) and high optical spectrum resolving power of Fabry-Perot Interferometer (FPI), a method to simulate wind velocity with simple equipment is discussed. Dopplers shift of airglow is simulated by changing the modulation current of LD, which leads to change in frequency of output laser. The equivalent wind velocity can be derived by analyzing interferometric images obtained by FPI. Relative errors of simulated velocities are less than 6.5%, and the least simulated velocity is 20.01m/s. The results agree with the liner modulation property of LD perfectly. This method can be applied in analysis and evaluation of the principles, data processing methods, system performance and measurement errors.
Detection of reactive oxygen species (ROS) in mainstream cigarette smoke using fluorescent probe
XU Shi-jie, LIU li, TANG Jing, LI Song-zan
2009, 30(2): 291-295.
Non-fluorescence probe dihydrorhodamine 6G (dR6G) can be oxidized to fluorescent rhodamine 6G. In the process, each molecule reacts with two active oxygen molecules. The probe can be used to detect ROS in mainstream cigarette smoke by using derivative fluorescence method. We detected the contents of ROS in mainstream smoke from the 4 types of cigarettes purchased in market. The ROS content is (59.935.32)nmol,(55.986.17)nmol,(54.787.82)nmol, (40.876.43)nmol respectively. The results show that the amount of ROS is dependent on the types of tobacco and cigarette production technology. This realtime ROS detection method in mainstream smoke by fluorescence characteristic is fast and sensitive.
Night Vision
Mass spectrometric analysis for gas components baked from glass cementation cathode module
XU Jiang-tao
2009, 30(2): 296-299.
The gas components released from the glass cementation cathode module during the high temperature bake was analyzed with a mass spectrometer to resolve the problem of low GaAs photocathode emission sensitivity. The atomic level surface of GaAs electronic emission layer was obtained. The analysis result indicates that the degas temperature of the module surface is 150℃, the degas temperature of the material is 450℃, the temperature for clean surface is 580℃, and As evaporation occurs on the GaAs emission emission layer at the temperature higher than 650℃. It shows that the strict control of the clean temperature of the emission layer surface is the key to obtain high-performance sensitive cathode.
Method of choosing ideal imaging plane in image intensifier MTF measurement
BAI Xiao-feng
2009, 30(2): 300-303.
Since MTF measurement is important for evaluating the imaging quality of low-light-level image intensifier, the imaging plane position in the measurement system is adjusted to obtain accurate MTF measurement results. The optical imaging feature of LLL image intensifier MTF measurement system was analyzed, and the aberration of the optical system was discussed. The ideal setting of the imaging plane in LLL image intensifier MTF measurement was implemented by the method of the average middle value. By comparing the result with the known value of the image intensifier, this method is proved to be accurate.
Optical Element and Fabrication
Process design for micro core mould of binary optical element
GONG Yong-qing, LIU Zhi-huai, GAO Yi-qing, LUO Ning-ning, LI Ping-gui
2009, 30(2): 304-308.
Based on the spatial light modulation characteristics of digital micro-mirror device (DMD), a process design method for micro core mould of binary optical element (BOE) is proposed. A computer program was designed to simulate the vectograms of different BOEs such as Fresnel lens, Dammann grating, and Ronchi grating. The BOE pattern displayed on DMD was imaged on the substrate coated with photoresist by 14× reduction optical system, and the BOE mask can be obtained after development, fixation and electrochemical etching. By using DMD system, BOEs were fabricated with low cost and high efficiency, and fabrication parameters could be controlled,which were suitable for many optical systems.
High precision glass drilling technology
LIU Jun-han, YAN De-quan, ZHOU Yang
2009, 30(2): 309-312.
In the processing of common optical elements,there are many problems in drilling high-precision holes on the glass ceramics with the traditional drilling technology. The common problems are ellipse,decentration,taper and edge cracks et al. To resolve these problems, a new drilling technology was used, and a high-precision inner hole, whose diameter tolerance and coaxiality were 0.01mm, was prepared on a glass ceramic by using a simple drilling machine and a universal cylindrical grinder. The production practice shows that this process is repetitive and steady. The problems existing in the glass drilling were solved and the high-precision inner holes were obtained.
Fiber Sensing and Optical Communication
Design of optical Interleaver based on non-uniformly sampled FBG
ZHANG Xing-jiao, YE Zhi-qing
2009, 30(2): 313-316.
The Interleaver used in the multiplexer or demultiplexer is a key device of the future DWDM for the limited bandwidth resources in fiber-optic communication. Based on the coupling-mode theory, the transmission properties of nonuniformly sampled FBGs are numerically simulated with the transfer matrix method. The basic principle of optical Interleaver based on non-uniform sampled fiber gratings(SFBG)is introduced. The design example, whose channel interval is 0.8nm and the peak reflectivity is 80%~95%, is presented. The channel intervals are steady and uniform. The delay spectra of each channel are congruous, and the delay dither is less than 100ps.
Design of single-mode all-fiber hydrophone and its drive circuit
YANG Wu-ying, ZUO Hong-ji, ZHENG Li, CANG Yu-ping, LI Jin-ke, CHEN Liang-yi
2009, 30(2): 317-320.
The design method of the common single-mode all-fiber (SMF) hydrophone and its drive circuit is provided. During the process of the design, SMF whose transmission wavelength is 1550nm was chosen,the MQW-DFB(multiquantum well distributed feed back)semiconductor laser was taken as the light source, MAX3263 and MAX038 were selected to design the laser driver and high-performance sine-wave signal generator, respectively, and InGaAs PIN was taken as the optoelectronic detector. The experiments indicate that the sensitivity of the fiber hydrophone presented in this paper is higher than that of the standard hydrophone (piezoelectricity type) by 50dB~60dB(1kHz~30kHz).
Weak pressure sensor based on photonic crystal fibers
PENG Hui, WEN Ke, YANG Zheng-chun, LIANG Xiao-ming
2009, 30(2): 321-324.
In order to analyze the characteristics of photonic crystal fiber under weak pressure,the relationship between the birefringence and the pressure was simulated with the finite element method.The birefringence in photonic crystal fibers is more sensitive than that in conventional step-index fibers,but the birefringence change caused by the weak pressure is less and it is difficult to measure the variation of pressure by Bragg wavelength measurement.The polarization dependent loss was used to measure the birefringence change caused by the external weak pressure.The simulated results show that the measured sensitivity can reach 0.75dB/MPa.
Laser Technology
Numerical simulation of ultrafast energy transport in monocrystalline silicon films under femtosecond laser irradiation
LIU Guo-dong, LUO Fu, WANG Gui-bing, LI Jian-feng, FU Bo
2009, 30(2): 325-329.
The process of the ultrafast energy transport in monocrystalline silicon submicron films irradiated with femtosecond laser was simulated using the carrier transport model based on the Boltzmann transport equation. The effects of different irradiation energy density and laser wavelength on the carrier density and the process of temperature ultrafast variation were investigated. The numerical calculation results show that, irradiated at 800 nm, the incident energy density influences the peaks of the carrier density and temperature only, but the occurrence time of their peaks does not change. The recovery process toward the equilibrium state is hardly influenced by the incident energy density. Under the irradiation of different wavelengths, the higher the photon energy is, the less time the carrier density and temperature take to reach the peak values, the bigger the corresponding peak appears and the faster the attenuation velocity becomes. The time constant of the fast attenuation is equal to the carrier energy relaxation time when the incident photon energy is larger than the band-gap of the monocrystalline silicon.
Intelligent test system for performance parameter of laser
WANG Guo-fu, OUYANG Shan, LIU Qing-hua, DING Yong, CHEN Liang-yi
2009, 30(2): 330-333.
To solve the problems existing in the present test system such as low testing precision and simple function, a new intelligent test system is developed, which involves control technology, quick and convenient WIN32 computer software and a special beam splitter system. It can simultaneously measure optical axis parallelism, width and energy of the pulse, beam divergence, beam axis stability, and system performance. A high-powered infrared autocollimator is adopted to ensure 2″ of spatial resolution, a 15GHz oscilloscope is used to capture the laser pulse as narrow as 100ps, and an accurate laser power meter with large dynamic range is used to obtain accurate energy measurement of the laser pulse. The system is checked and accepted, and all the performance parameters meet the design requirements.
Application of differential laser Doppler velocimeter in solid velocity measurement
ZHOU Jian, LONG Xing-wu
2009, 30(2): 334-337.
An experiment was carried out by differential measurement and backscattering mode. The Doppler signal was acquired by the data acquisition board PCI DAS-4020, and the signal data filtering was performed to improve SNR. The frequency spectrum was acquired by fast Fourier transform, and the calculated velocity of the moving target was compared with the actual velocity. The results show that the system is applicable for the velocity measurement of solid moving surfaces, and the accuracy can reach 2.2%.
Light field distribution in side-pumped rod-shaped laser medium of laser diode arrays
ZHANG Biao, GAO Wei, YANG Zhao-jin, YANG Hong-ru
2009, 30(2): 338-343.
The numerical model of the light field distribution in the side-pumped laser medium of LD was established. An analytical solution for the pumping light refraction in the rod-shaped gain medium was simplified with ray tracing. The normalized distribution of pumping light in the medium was simulated numerically with Matlab. The selection principle to acquire the parameters of high-quality and high-energy laser output is proposed. The influence of the structural parameters on the distribution of pumping light is analyzed. The experiment result shows that the gain distribution of pumping light in the laser medium is satisfactory when the radius of the beam waist is 1μm, the number of LD is 40, the radius of the medium is 1.5mm, the pumping distance between the luminous surface and the medium is 0.5mm and the absorption coefficient of the medium is 2cm-1 ~6cm-1.
Acoustic wave resonance in CuBr laser discharge tube
MA Tao
2009, 30(2): 344-347.
A model of acoustic oscillations was presented for the CuBr laser discharge tube. An analytical expression of the acoustic waves was given. The relation between natural frequency and discharge frequency was described. It is found that the acoustic oscillations lead to the redistribution of the laser medium in the discharge tube, which influences laser output power.
Infrared Imaging Technology and Application
Uncooled infrared focal plane array detector module with the self-adaptive non-uniformity correction function
JIN Wei-qi, CAO Yang, LIU Chong-liang, LIU Xiu, DONG Li-quan, ZHANG Chang-quan
2009, 30(2): 348-352.
Non-uniformity correction (NUC) for the IRFPA has become one of the most important issues for defense electro-optics. Scene-based non-uniformity correction (SBNUC) is the major trend of NUC techniques in the future. In this paper, the author introduces the research progress in SBNUC technique based on the constant statistic constraint, neural network, and motion estimation. The method to combine SBNUC algorithms with infrared focal plate array (IRFPA) detector module is presented, and the uncooled IRFPA detector module with self-adaptive non-uniformity correction function is developed. The proposed algorithms can use only image sequence information to calculate the gain/bias parameters and update them group-by-group or frame-by-frame, compensating the FPN temporal variation effectively. The detector module can improve the image performance of the imaging system significantly, and ensure the stability of the imaging system with the scene motion dynamically.
Error analysis for gate centroid tracking algorithm of infrared imaging
WANG Ke-wei, MA Chao-jie, CHEN Wei, ZHANG Fan
2009, 30(2): 353-356.
The principle of a gate centroid tracking algorithm is introduced. Its tracking error model was established. The error of the gate centroid tracking algorithm in infrared imaging was discussed and analyzed. The centroid tracking error decreases when there is less misjudgment probability, more target pixels and fewer background pixels in the gate. The correct match coefficient increases when there is a greater SNR, fewer correlated searches and more pixels in correlated calculation. Test results show that the algorithm can reduce tracking error, improve tracking accuracy and stability.
Adaptive algorithm for infrared target enhancement
GUO Jia, QIN Wen-gang, LIU Wei-guo
2009, 30(2): 357-360.
Since traditional histogram equalization and gray-scale transformation algorithms could not realize the enhancement of the target in the infrared image effectively, an adaptive algorithm for infrared target enhancement is presented. The algorithm is used to filter out random noise in infrared image by median filtering, and divide the image into target section and background section by histogram, suppress background and enhance target feature by linear weighted overlap. The experimental result shows that this algorithm could automatically choose the threshold of histogram segmentation according to the gray scale characteristic of the target. It can also increase the contrast, decrease the noise and suppress the background. The algorithm performs well for target enhancement in the infrared image whose histogram has two local peaks when target and background pixels are similar.