2008 Vol. 29, No. 1
Display Method:
2008, 29(1): 1-4.
Abstract:
Based on the application demands of high performance CCD imaging and high performance low-light ICCD imaging, a high performance cooling digital video CCD imaging module was developed based on CCD device of industrial level. Some design features in the imaging module such as high performance large format CCD array, low noise drive circuit, miniaturized low power consumption cooling technology and customized cooling cavity structure are introduced. It will find wide applications in military, industrial, biomedical and scientific research fields.
Based on the application demands of high performance CCD imaging and high performance low-light ICCD imaging, a high performance cooling digital video CCD imaging module was developed based on CCD device of industrial level. Some design features in the imaging module such as high performance large format CCD array, low noise drive circuit, miniaturized low power consumption cooling technology and customized cooling cavity structure are introduced. It will find wide applications in military, industrial, biomedical and scientific research fields.
2008, 29(1): 5-8.
Abstract:
Signature selection is very important in the target recognition, especially for the wavelet moment invariants which have three parameters (m,n,q). The absolute resovable signature selection algorithm under the multi-class mode for target recognition is put forward and the proper range for m,n,q values during the image digitalization processing is given, based on the signature selection in two class mode. The experiments show that this method can be successfully used in the recognition of multi-class targets, whether the multi-class targets are different, similar or mixed types.
Signature selection is very important in the target recognition, especially for the wavelet moment invariants which have three parameters (m,n,q). The absolute resovable signature selection algorithm under the multi-class mode for target recognition is put forward and the proper range for m,n,q values during the image digitalization processing is given, based on the signature selection in two class mode. The experiments show that this method can be successfully used in the recognition of multi-class targets, whether the multi-class targets are different, similar or mixed types.
2008, 29(1): 9-13.
Abstract:
Small target detection is an interesting subject in computer vision. Traditional methods can not be used to detect specific target with interested size when there are many targets of different sizes in an image. Neither can they be used effectively to detect an approaching target whose image size become larger and larger. In order to solve these problems, a new method of small target detection is presented based on the positive and negative LOG (PNLOG) operator. With the new method, the true target is detected by the Top-Hat algorithm in several initial images based on the rough linear movement of the target in a short period of time. The parameters of PNLOG operator are defined based on the target features. The follow-up images is continuously detected by defined PNLOG operator to determine the position of the true target. The experimental results show that the new method has great capability in real-time detection, detection precision and anti-jamming.
Small target detection is an interesting subject in computer vision. Traditional methods can not be used to detect specific target with interested size when there are many targets of different sizes in an image. Neither can they be used effectively to detect an approaching target whose image size become larger and larger. In order to solve these problems, a new method of small target detection is presented based on the positive and negative LOG (PNLOG) operator. With the new method, the true target is detected by the Top-Hat algorithm in several initial images based on the rough linear movement of the target in a short period of time. The parameters of PNLOG operator are defined based on the target features. The follow-up images is continuously detected by defined PNLOG operator to determine the position of the true target. The experimental results show that the new method has great capability in real-time detection, detection precision and anti-jamming.
2008, 29(1): 14-17.
Abstract:
Image edge recognition is an important part of image processing. A gradient segmentation algorithm based on the depth-first traversal of images is presented. In this method, the data structure of the pixel is defined firstly, the four pixels around an arbitrary point of an image are estimated and the gradient values of the pixels are acquired. If the pixel satisfies the feature of an edge, the edge perpendicular to the directions of gradient is processed by depth-first traversal, and the pixels are marked at the same time. If there is no pixel to satisfy the feature in the direction, it will withdraw, and then the depth-first traversal will be implemented from the direction next to the maximum gradient, marking the pixel as corner, until the traversal of the whole image is completed. The experimental results show that edges and corners of an image can be segmented clearly and easily identified.
Image edge recognition is an important part of image processing. A gradient segmentation algorithm based on the depth-first traversal of images is presented. In this method, the data structure of the pixel is defined firstly, the four pixels around an arbitrary point of an image are estimated and the gradient values of the pixels are acquired. If the pixel satisfies the feature of an edge, the edge perpendicular to the directions of gradient is processed by depth-first traversal, and the pixels are marked at the same time. If there is no pixel to satisfy the feature in the direction, it will withdraw, and then the depth-first traversal will be implemented from the direction next to the maximum gradient, marking the pixel as corner, until the traversal of the whole image is completed. The experimental results show that edges and corners of an image can be segmented clearly and easily identified.
2008, 29(1): 18-22.
Abstract:
The characteristics of the multi-gimbal structures were analyzed based on the kinematics theory of LOS stabilization and tracking, and the selection principle for gimbal structures was given. Using the PIOGRAM method, a typical two-axis gimbal structure, three axes two-gimbal structure and two axes four-gimbal structure were discussed. The problems such as gimbal lock and the blind area of tracking were expatiated by the relationship of angle and rate. The requirements for different platforms and target motions were obtained and they could be used for selecting proper gimbal structure for specific application. The method is also applicable to other multi-axis structure and can be used for analyzing geometric.
The characteristics of the multi-gimbal structures were analyzed based on the kinematics theory of LOS stabilization and tracking, and the selection principle for gimbal structures was given. Using the PIOGRAM method, a typical two-axis gimbal structure, three axes two-gimbal structure and two axes four-gimbal structure were discussed. The problems such as gimbal lock and the blind area of tracking were expatiated by the relationship of angle and rate. The requirements for different platforms and target motions were obtained and they could be used for selecting proper gimbal structure for specific application. The method is also applicable to other multi-axis structure and can be used for analyzing geometric.
2008, 29(1): 23-26.
Abstract:
The selection of the dampers for two axes four-gimbal electro-optical (EO) pod is investigated according to vibration theory. A frequency scanning vibration test was carried out for a helicopter pod whose inner gimbal was connected with the outer gimbal by rigid link. The resonant frequency and amplification factors were measured and the amplification curves were drawn. Using the amplification curves, the stiffness of the rigid link between the inner and outer gimbals of the pod in three direction was calculated. With the stiffness value of the damper, using cascade spring connection calculation method, the three direction rigidity and resonant frequency of the pod were calculated again with damper installed. The pod was tested again and the results indicate that the resonance frequency and amplification factor meet the requirement. It is concluded that three factors shall be considered for the selection of dampers, its amplification range shall be within the servo bandwidth, system resonant frequency shall avoid external disturbance frequency, and amplification factor shall be minimized.
The selection of the dampers for two axes four-gimbal electro-optical (EO) pod is investigated according to vibration theory. A frequency scanning vibration test was carried out for a helicopter pod whose inner gimbal was connected with the outer gimbal by rigid link. The resonant frequency and amplification factors were measured and the amplification curves were drawn. Using the amplification curves, the stiffness of the rigid link between the inner and outer gimbals of the pod in three direction was calculated. With the stiffness value of the damper, using cascade spring connection calculation method, the three direction rigidity and resonant frequency of the pod were calculated again with damper installed. The pod was tested again and the results indicate that the resonance frequency and amplification factor meet the requirement. It is concluded that three factors shall be considered for the selection of dampers, its amplification range shall be within the servo bandwidth, system resonant frequency shall avoid external disturbance frequency, and amplification factor shall be minimized.
2008, 29(1): 27-30.
Abstract:
High-speed photography applied in electrical explosive loaded multi-layer aluminum target is described. The moving fragment images and ejection of material produced by striking Mylar film on two-or-three-layer aluminum target was obtained with high-speed photography and laser shadowgraph in various conditions, such as different voltages of explosive bridge, thicknesses and spaces between aluminum plates. The speed of the fragments and the micro surge were acquired in the experiment.
High-speed photography applied in electrical explosive loaded multi-layer aluminum target is described. The moving fragment images and ejection of material produced by striking Mylar film on two-or-three-layer aluminum target was obtained with high-speed photography and laser shadowgraph in various conditions, such as different voltages of explosive bridge, thicknesses and spaces between aluminum plates. The speed of the fragments and the micro surge were acquired in the experiment.
2008, 29(1): 31-34.
Abstract:
A parallel laser beam splitter was designed based on the characteristics of birefringent crystal for applications such as wavefront shearing interference, dual light beam curved reflective surface measurement and step height measurement. When a plane wave or laser beam enters a birefringent crystal, its mutually perpendicular polarization components will propagate in different states to generate two beams after they exit the crystal. The splitter consists of a single crystal plate. Its splitting principle was described, and the relationship between the splitting distance, the direction of optical axis, the thickness of the plate, and the incidence angle was deduced. The variation law of splitting distance with the main design parameters was analyzed. Lab test was conducted on the splitter, and the analysis results were verified.
A parallel laser beam splitter was designed based on the characteristics of birefringent crystal for applications such as wavefront shearing interference, dual light beam curved reflective surface measurement and step height measurement. When a plane wave or laser beam enters a birefringent crystal, its mutually perpendicular polarization components will propagate in different states to generate two beams after they exit the crystal. The splitter consists of a single crystal plate. Its splitting principle was described, and the relationship between the splitting distance, the direction of optical axis, the thickness of the plate, and the incidence angle was deduced. The variation law of splitting distance with the main design parameters was analyzed. Lab test was conducted on the splitter, and the analysis results were verified.
2008, 29(1): 35-39.
Abstract:
Polarization BRDF can be used to describe the space distribution of radiation intensity of objects and it includes plenty of polarization information. Compared with the scalar BRDF, the polarimetric BRDF can show the light scattering of an object surface more accurately and completely．A polarimetric BRDF measurement system based on dual rotating retarder configuration was designed. The polarization state of incident and scattering light was modulated by synchronously rotating wave plates to acquire a series of changing light intensity. The polarimetric BRDF of the sample was obtained by calculating the Fourier decomposition coefficients of the light intensity. A pair of orthogonal mirrors were mounted in the system to minimize the influence of back-scattering light from some other components in the system. The precision of measurement system was demonstrated by the measurement result of the aluminium-plate polarimetric BRDF.
Polarization BRDF can be used to describe the space distribution of radiation intensity of objects and it includes plenty of polarization information. Compared with the scalar BRDF, the polarimetric BRDF can show the light scattering of an object surface more accurately and completely．A polarimetric BRDF measurement system based on dual rotating retarder configuration was designed. The polarization state of incident and scattering light was modulated by synchronously rotating wave plates to acquire a series of changing light intensity. The polarimetric BRDF of the sample was obtained by calculating the Fourier decomposition coefficients of the light intensity. A pair of orthogonal mirrors were mounted in the system to minimize the influence of back-scattering light from some other components in the system. The precision of measurement system was demonstrated by the measurement result of the aluminium-plate polarimetric BRDF.
2008, 29(1): 40-44.
Abstract:
Compared to conventional optics, binary optical elements have some unique advantages. A reflective and diffractive hybrid telescope with an aperture of 25m was designed, with two binary optical elements as its objective and eyepiece. The dispersed spot size and MTF of the telescope meet the requirements. The high order diffractive lenses take the place of conventional diffractive lenses to improve the performance of the system, and the telescope achieves a broader bandwidth. The results show that the modified system can provide almost diffractionlimited imaging quality within the range of single-band, multi-band or continuous coverage.
Compared to conventional optics, binary optical elements have some unique advantages. A reflective and diffractive hybrid telescope with an aperture of 25m was designed, with two binary optical elements as its objective and eyepiece. The dispersed spot size and MTF of the telescope meet the requirements. The high order diffractive lenses take the place of conventional diffractive lenses to improve the performance of the system, and the telescope achieves a broader bandwidth. The results show that the modified system can provide almost diffractionlimited imaging quality within the range of single-band, multi-band or continuous coverage.
2008, 29(1): 45-47.
Abstract:
Based on the zoom equation, the dynamic optics principle and the process analysis of the Gauss calculation for zoom systems, it is pointed out that the primary factors which influence the cam curve are the focal length of the zoom lens group and compensating lens group, and the distance between them. The relationships between the three parameters were discussed. The method to optimize the cam curve is proposed.
Based on the zoom equation, the dynamic optics principle and the process analysis of the Gauss calculation for zoom systems, it is pointed out that the primary factors which influence the cam curve are the focal length of the zoom lens group and compensating lens group, and the distance between them. The relationships between the three parameters were discussed. The method to optimize the cam curve is proposed.
2008, 29(1): 48-51.
Abstract:
The photocathode sensitivity is one of the most important and fundamental parameters of image intensifiers, which determines the performance of the photo-electronic imaging system under low-light-level conditions. Based on the physical model of semiconductor optoelectronic emission and Plank theory of black-body radiation, the effect of 5 sub-processes on photocathode quantum efficiency is summarized. Several expressions are given to calculate the sensitivity limit under the assumption of 100% sub-quantum efficiencies in the 5 sub-processes. The ultimate sensitivity of 6569μA/lm is obtained for an extended blue GaAs photocathode in the waveband of (0.41～0.93)μm.
The photocathode sensitivity is one of the most important and fundamental parameters of image intensifiers, which determines the performance of the photo-electronic imaging system under low-light-level conditions. Based on the physical model of semiconductor optoelectronic emission and Plank theory of black-body radiation, the effect of 5 sub-processes on photocathode quantum efficiency is summarized. Several expressions are given to calculate the sensitivity limit under the assumption of 100% sub-quantum efficiencies in the 5 sub-processes. The ultimate sensitivity of 6569μA/lm is obtained for an extended blue GaAs photocathode in the waveband of (0.41～0.93)μm.
2008, 29(1): 52-56.
Abstract:
Aiming at geosynchronous orbit infrared detection system, the infrared detection performance of the ballistic missile plume is analyzed. The atmospheric transmittance and the background radiance at different heights and different sun zenith angles were computed with the atmospheric radiance model software of PCModWin. According to the obtained results, the performance indexes of infrared system for the plume detection of the ballistic missile, including the effective range, SNR (signal-to-noise ratio) and SCR (signal-to-clutter ratio), were analyzed. The results indicate that SCR performance index can meet the needs of the infrared detection system, but the performance of SNR and the effective range are not satisfactory. The performance of the infrared detection system can be improving the parameters of the sensors and the optical system.
Aiming at geosynchronous orbit infrared detection system, the infrared detection performance of the ballistic missile plume is analyzed. The atmospheric transmittance and the background radiance at different heights and different sun zenith angles were computed with the atmospheric radiance model software of PCModWin. According to the obtained results, the performance indexes of infrared system for the plume detection of the ballistic missile, including the effective range, SNR (signal-to-noise ratio) and SCR (signal-to-clutter ratio), were analyzed. The results indicate that SCR performance index can meet the needs of the infrared detection system, but the performance of SNR and the effective range are not satisfactory. The performance of the infrared detection system can be improving the parameters of the sensors and the optical system.
2008, 29(1): 57-61.
Abstract:
Chemical vapor deposited zinc sulfide (CVD ZnS) is a long-wave infrared material with excellent optical and mechanical properties. CVD ZnS windows and domes with bulk size up to 250mm×15mm were prepared by chemical vapor deposition and hot isolated pressing. Technical issues for preparation of CVD ZnS, including chemical reaction, hot isolated pressing, control of flow pattern and equipment, are discussed. Optical and mechanical properties of CVD ZnS were measured and analyzed. The full-band transmittance of the samples is close to the theoretical value of ZnS, the inhomogeneity of refractive index at 0.6328 μm is less than 2×10-5, the bulk absorption at 1.06μm is 2×10-3cm-1 and bending strength is 104MPa. The result indicates that the quality of CVD ZnS is similar to that of American products.
Chemical vapor deposited zinc sulfide (CVD ZnS) is a long-wave infrared material with excellent optical and mechanical properties. CVD ZnS windows and domes with bulk size up to 250mm×15mm were prepared by chemical vapor deposition and hot isolated pressing. Technical issues for preparation of CVD ZnS, including chemical reaction, hot isolated pressing, control of flow pattern and equipment, are discussed. Optical and mechanical properties of CVD ZnS were measured and analyzed. The full-band transmittance of the samples is close to the theoretical value of ZnS, the inhomogeneity of refractive index at 0.6328 μm is less than 2×10-5, the bulk absorption at 1.06μm is 2×10-3cm-1 and bending strength is 104MPa. The result indicates that the quality of CVD ZnS is similar to that of American products.
2008, 29(1): 62-66.
Abstract:
To overcome mass data, long duration, instability and uncertainty in the test of triangle orientation discrimination (TOD), a simulation method for IR scanning imaging systems is presented. A simulation platform for predicting IR imaging systems performance was established,and the triangle pattern images were discriminated by human eyes. According to the results, training was carried out for the neural network. Based on the predictive method of TOD by the neural network, the direction of the simulation spline is discriminated, the correct discrimination probability was obtained by utilizing the statistical method, and the TOD prediction curve is achieved. Experimental results show that the predicted TOD curve is consistent with the measurement.
To overcome mass data, long duration, instability and uncertainty in the test of triangle orientation discrimination (TOD), a simulation method for IR scanning imaging systems is presented. A simulation platform for predicting IR imaging systems performance was established,and the triangle pattern images were discriminated by human eyes. According to the results, training was carried out for the neural network. Based on the predictive method of TOD by the neural network, the direction of the simulation spline is discriminated, the correct discrimination probability was obtained by utilizing the statistical method, and the TOD prediction curve is achieved. Experimental results show that the predicted TOD curve is consistent with the measurement.
2008, 29(1): 67-71.
Abstract:
The structure of the 3-mirror folded resonator was optimized for Laser-diode end-pumped Nd∶YVO4/KTP intracavity frequency-doubled laser. The influence of parameters including the resonator length, curvature radii of mirrors, Nd∶YVO4 and KTP thermal effect on the stable area of the laser resonator and the basic mode size of Nd∶YVO4 crystal was investigated. The research shows that the experiment result is consistent with that of the theoretical analysis. The red laser output powers at different folded angles of the folded resonator were compared, the effective frequency-doubled efficiency of 10.8% was obtained at the optimal folded angle 25°. The experimental result was explained theoretically with the relation between the polarization property of the fundamental laser beam and the phase matching of KTP.
The structure of the 3-mirror folded resonator was optimized for Laser-diode end-pumped Nd∶YVO4/KTP intracavity frequency-doubled laser. The influence of parameters including the resonator length, curvature radii of mirrors, Nd∶YVO4 and KTP thermal effect on the stable area of the laser resonator and the basic mode size of Nd∶YVO4 crystal was investigated. The research shows that the experiment result is consistent with that of the theoretical analysis. The red laser output powers at different folded angles of the folded resonator were compared, the effective frequency-doubled efficiency of 10.8% was obtained at the optimal folded angle 25°. The experimental result was explained theoretically with the relation between the polarization property of the fundamental laser beam and the phase matching of KTP.
2008, 29(1): 72-75.
Abstract:
In order to investigate the output stability of Q-switched diode-pumped laser (DPL) pulse, the tradition detection circuit of the silicon photodiode was analyzed with the circuit mesh method. It is found that the traditional detection circuit is unable to detect the high frequency noise signal generated by the multi-longitudinal modes in the laser pulse. According to the analysis result, the silicon photodiode detection circuit was improved, and (1～2)GHz high frequency noise signal of a Q-switched laser was collected by the high speed sampling oscilloscope.
In order to investigate the output stability of Q-switched diode-pumped laser (DPL) pulse, the tradition detection circuit of the silicon photodiode was analyzed with the circuit mesh method. It is found that the traditional detection circuit is unable to detect the high frequency noise signal generated by the multi-longitudinal modes in the laser pulse. According to the analysis result, the silicon photodiode detection circuit was improved, and (1～2)GHz high frequency noise signal of a Q-switched laser was collected by the high speed sampling oscilloscope.
2008, 29(1): 76-80.
Abstract:
The conventional technique for the laser cladding ceramic-metal composite coating mainly has two disadvantages. Firstly, the efficiency of its powder deposition is low and it limits the cladding rate, makes the process rather expensive for cladding on large areas. Secondly, due to some inherent characteristics in laser cladding technique, such as rapid heating and rapid solidification, the residual stress induced during laser cladding could lead to the crack formation in the composite coatings. The status quo of the domestic and foreign research on laser cladding ceramic-metal composite coating technique is reviewed. The existing problems are pointed out and a new solution for laser induction hybrid rapid cladding (LIHRC) is put forward, which preheats the substrate before the laser cladding. The efficiency of this new solution is higher than that of the conventional laser cladding and crack-free ceramic-metal composite coatings prepared by LIHRC.
The conventional technique for the laser cladding ceramic-metal composite coating mainly has two disadvantages. Firstly, the efficiency of its powder deposition is low and it limits the cladding rate, makes the process rather expensive for cladding on large areas. Secondly, due to some inherent characteristics in laser cladding technique, such as rapid heating and rapid solidification, the residual stress induced during laser cladding could lead to the crack formation in the composite coatings. The status quo of the domestic and foreign research on laser cladding ceramic-metal composite coating technique is reviewed. The existing problems are pointed out and a new solution for laser induction hybrid rapid cladding (LIHRC) is put forward, which preheats the substrate before the laser cladding. The efficiency of this new solution is higher than that of the conventional laser cladding and crack-free ceramic-metal composite coatings prepared by LIHRC.
2008, 29(1): 81-85.
Abstract:
The anisotropic Yb∶KGW laser crystal may have the zero thermal lens effect in some propagation directions, according to the measurement results of Biswal et al and Pujol et al. The thermal expansion tensors of Yb∶KGW crystals mentioned in these two references were obtained by least square and tensor rotation methods respectively. And the athermal directions were calculated on the basis of the thermal expansion tensors. The comparison and analysis show that, although there is some difference between individual crystals, this kind of crystals generally has only two athermal directions instead of four athermal directions calculated by Biswal et al, that is to say, the angles between these two athermal directions and p axis are around ±20° in the p-g plane when light is polarized in m direction. Besides, the calculated thermo-optic properties in certain directions with thermal expansion tensor taken into account are consistent with the laser thermal lensing experimental results reported by Swedish Hellstrom et al.
The anisotropic Yb∶KGW laser crystal may have the zero thermal lens effect in some propagation directions, according to the measurement results of Biswal et al and Pujol et al. The thermal expansion tensors of Yb∶KGW crystals mentioned in these two references were obtained by least square and tensor rotation methods respectively. And the athermal directions were calculated on the basis of the thermal expansion tensors. The comparison and analysis show that, although there is some difference between individual crystals, this kind of crystals generally has only two athermal directions instead of four athermal directions calculated by Biswal et al, that is to say, the angles between these two athermal directions and p axis are around ±20° in the p-g plane when light is polarized in m direction. Besides, the calculated thermo-optic properties in certain directions with thermal expansion tensor taken into account are consistent with the laser thermal lensing experimental results reported by Swedish Hellstrom et al.
2008, 29(1): 86-89.
Abstract:
The operation principle of the passive angle jamming system (optical fiber laser jamming system) by changing the laser guiding angle was presented, system jamming effectiveness parameters such as the power ratio and the delay time were discussed. The analysis shows that the laser power reflected from the decoy can meet the requirement if the coverage of the optical fiber receiving system and reflectance of the decoy are properly selected, and the delay time of several microseconds is far less than the gate width of the target required by seeker, which makes the incident probability of laser echo into the gate from the decoy quite high. The feasibility of the jamming system is proved. Other measures such as the camouflage or displacing laser into open space could make the jamming system more effective.
The operation principle of the passive angle jamming system (optical fiber laser jamming system) by changing the laser guiding angle was presented, system jamming effectiveness parameters such as the power ratio and the delay time were discussed. The analysis shows that the laser power reflected from the decoy can meet the requirement if the coverage of the optical fiber receiving system and reflectance of the decoy are properly selected, and the delay time of several microseconds is far less than the gate width of the target required by seeker, which makes the incident probability of laser echo into the gate from the decoy quite high. The feasibility of the jamming system is proved. Other measures such as the camouflage or displacing laser into open space could make the jamming system more effective.
2008, 29(1): 90-95.
Abstract:
The configuration, failure mechanism and heat generation mechanism of highpower diode laser (HDL) are described. The lifetime assessment is discussed, including the methods used and the difficulties encountered in the assessment. The status quo of such assessment at home and abroad is given. Some suggestions on lifetime assessment and test are given. The development of reliability and lifetime test for high power diode laser is promoted by its application in civilian industry, military and space filed. With the increasing of reliability and lifetime, high power diode laser will find more applications.
The configuration, failure mechanism and heat generation mechanism of highpower diode laser (HDL) are described. The lifetime assessment is discussed, including the methods used and the difficulties encountered in the assessment. The status quo of such assessment at home and abroad is given. Some suggestions on lifetime assessment and test are given. The development of reliability and lifetime test for high power diode laser is promoted by its application in civilian industry, military and space filed. With the increasing of reliability and lifetime, high power diode laser will find more applications.
2008, 29(1): 96-100.
Abstract:
In order to study the structural feature of the atmospheric boundary layer (ABL) over Beijing and the aerosol extinction characteristic in it, ABL over Beijing was observed with a potable Mie LIDAR in the summer of 2004. The vertical distribution of extinction properties and the height of ABL over the observation site were inverted. And the influences induced by meteorological conditions and human activities on the ABL structure were analyzed. The data indicates that the variation of ABL over Beijing in the daytime in summer is obvious. With meteorological parameters, the detected data of ABL heights and aerosol optical depth are presented and discussed. The research result shows that the ABL height is always less than 1.8km, its average height is 0.68km and the aerosol optical depths within 3km are about 0.3.
In order to study the structural feature of the atmospheric boundary layer (ABL) over Beijing and the aerosol extinction characteristic in it, ABL over Beijing was observed with a potable Mie LIDAR in the summer of 2004. The vertical distribution of extinction properties and the height of ABL over the observation site were inverted. And the influences induced by meteorological conditions and human activities on the ABL structure were analyzed. The data indicates that the variation of ABL over Beijing in the daytime in summer is obvious. With meteorological parameters, the detected data of ABL heights and aerosol optical depth are presented and discussed. The research result shows that the ABL height is always less than 1.8km, its average height is 0.68km and the aerosol optical depths within 3km are about 0.3.
2008, 29(1): 101-104.
Abstract:
A new type of geophone is presented, based on the narrow band transmission and free of back reflection features of long period fiber grating. The acceleration sensitivity of the resonance wavelength of the long period fiber grating geophone system was deduced and analyzed with the phase matching of long period fiber grating as preconditions. The mechanic model of the long period fiber grating geophone was established and the transfer function of the geophone was deduced. Through simulating a simple example, the amplitudefrequency characteristics of the long period fiber grating geophone was obtained, and its feasibility was proved. The parameters such as length of the optical fiber, the mass of the mass block and the damping factor were improved to achieve proper frequency feature and sensitivity.
A new type of geophone is presented, based on the narrow band transmission and free of back reflection features of long period fiber grating. The acceleration sensitivity of the resonance wavelength of the long period fiber grating geophone system was deduced and analyzed with the phase matching of long period fiber grating as preconditions. The mechanic model of the long period fiber grating geophone was established and the transfer function of the geophone was deduced. Through simulating a simple example, the amplitudefrequency characteristics of the long period fiber grating geophone was obtained, and its feasibility was proved. The parameters such as length of the optical fiber, the mass of the mass block and the damping factor were improved to achieve proper frequency feature and sensitivity.
2008, 29(1): 105-109.
Abstract:
An effective method of passive temperature compensation was introduced and a compensation structure was designed to address the temperature cross sensitivity in the fiber Bragg grating (FBG) strain sensing. The curves of the compensation effect were analyzed with theoretical simulation in different M values. The optimized M value for compensation effect was obtained. The temperature curves in different pre-strains were obtained, the pre-strain value, which compensates the temperature completely, was found out. The phenomena of under-compensation and over-compensation were also analyzed. The temperature cross sensitivity existing in FBG sensing was effectively resolved via this method, and such temperature compensation can meet the demand of temperature stability in fiber sensing and communication.
An effective method of passive temperature compensation was introduced and a compensation structure was designed to address the temperature cross sensitivity in the fiber Bragg grating (FBG) strain sensing. The curves of the compensation effect were analyzed with theoretical simulation in different M values. The optimized M value for compensation effect was obtained. The temperature curves in different pre-strains were obtained, the pre-strain value, which compensates the temperature completely, was found out. The phenomena of under-compensation and over-compensation were also analyzed. The temperature cross sensitivity existing in FBG sensing was effectively resolved via this method, and such temperature compensation can meet the demand of temperature stability in fiber sensing and communication.
2008, 29(1): 110-114.
Abstract:
The aspheric primary mirror of new generation space camera is made up of some ultrathin segments. Since the mirror is ultrathin and the material of the mirror is brittle, it will be broken easily if the force exerted is not proper. Therefore, the damage threshold of ultrathin mirror should be studied. The concept of stress intensity factor in elasticity was applied to active optics and stress intensity factor was proved to be the material′s damage threshold. It is put forward that microcrack in the material is the major reason for breaking. A method to calculate stress intensity factor is introduced. At the end, the model of an ultrathin flat mirror was actually calculated, the relation between the damage threshold and the size, thickness, mounting and roughness of ultrathin flat mirror was achieved.
The aspheric primary mirror of new generation space camera is made up of some ultrathin segments. Since the mirror is ultrathin and the material of the mirror is brittle, it will be broken easily if the force exerted is not proper. Therefore, the damage threshold of ultrathin mirror should be studied. The concept of stress intensity factor in elasticity was applied to active optics and stress intensity factor was proved to be the material′s damage threshold. It is put forward that microcrack in the material is the major reason for breaking. A method to calculate stress intensity factor is introduced. At the end, the model of an ultrathin flat mirror was actually calculated, the relation between the damage threshold and the size, thickness, mounting and roughness of ultrathin flat mirror was achieved.
2008, 29(1): 115-119.
Abstract:
Based on the aberration sensitivity of structural parameter of offaxis threemirror anastigmat (TMA), the fabrication sequence of the primary mirror, the secondary mirror and the tertiary mirror is selected. The method is to determine the exact fabrication tolerance of each mirror through the optimization step by step. All three mirrors′ structural parameters are measured after fabrication, and these parameters are used to determine the assembly tolerance through optimization with optic system design software. By taking fabrication, alignment and design process into consideration, the fabrication and assembly tolerances are released to the maximal degree while the system specification is still achieved.
Based on the aberration sensitivity of structural parameter of offaxis threemirror anastigmat (TMA), the fabrication sequence of the primary mirror, the secondary mirror and the tertiary mirror is selected. The method is to determine the exact fabrication tolerance of each mirror through the optimization step by step. All three mirrors′ structural parameters are measured after fabrication, and these parameters are used to determine the assembly tolerance through optimization with optic system design software. By taking fabrication, alignment and design process into consideration, the fabrication and assembly tolerances are released to the maximal degree while the system specification is still achieved.
2008, 29(1): 120-123.
Abstract:
As an absolute measurement for the homogeneity of optical glass, the interference measurement is widely used because it can eliminate the form errors of both the interferometer reference surface and the part to be measured. The interference method to measure the homogeneity of optical glass was investigated, the error induced by material cutting angle was analyzed, and the method to correct the error was proposed. The stitch algorithm to measure the homogeneity of optical glass was also studied. The accurate measurement for the homogeneity of large-aperture optical glass was realized with a small-aperture interferometer.
As an absolute measurement for the homogeneity of optical glass, the interference measurement is widely used because it can eliminate the form errors of both the interferometer reference surface and the part to be measured. The interference method to measure the homogeneity of optical glass was investigated, the error induced by material cutting angle was analyzed, and the method to correct the error was proposed. The stitch algorithm to measure the homogeneity of optical glass was also studied. The accurate measurement for the homogeneity of large-aperture optical glass was realized with a small-aperture interferometer.
2008, 29(1): 124-127.
Abstract:
The image processing technology for determining the width of tilted objects was studied. A new method of object dimension algorithm-ring scanning method (RSM) is proposed. RSM can be used to determine the relation between an object and its edge points by circular search. The history, principle and application of the scanning algorithm are described.
The image processing technology for determining the width of tilted objects was studied. A new method of object dimension algorithm-ring scanning method (RSM) is proposed. RSM can be used to determine the relation between an object and its edge points by circular search. The history, principle and application of the scanning algorithm are described.
2008, 29(1): 128-130.
Abstract:
A novel method for phase measurement is presented. In the method, the position of the bell-like optoelectronic pulse peak signal from a coordinator gyroscope was accurately measured, and the position was used as time reference to measure the phase. The time interval between two signals and their phase lead or lag was determined. Some measures were taken to overcome the disturbance in the ambient environment. The experiment proves that the method enables simple circuit as well as fast, accurate and reliable measurement.
A novel method for phase measurement is presented. In the method, the position of the bell-like optoelectronic pulse peak signal from a coordinator gyroscope was accurately measured, and the position was used as time reference to measure the phase. The time interval between two signals and their phase lead or lag was determined. Some measures were taken to overcome the disturbance in the ambient environment. The experiment proves that the method enables simple circuit as well as fast, accurate and reliable measurement.
2008, 29(1): 131-135.
Abstract:
Precise measurement of the laser-induced damage threshold can be used to effectively evaluate the laser damage resistance of optical thin films. The determination of laser-induced damage threshold is dependent on the criteria to judge whether damage happens to the optical thin film or not. A measurement system with He-Ne laser scattered light was set up to detect the laser-induced damage threshold of optical thin films. The damage level of thin films was judged by measuring the variation of He-Ne laser scattered light energy at the same point on a sample. The damage threshold measurement for the diamond-like carbon films (DLC) and HfO2/SiO2 reflective coatings was performed. The measured result was compared with that of plasma spark method. Both of them have a preferable consistency. The analysis shows that the He-Ne laser scattering measurement system can be used effectively to determine laserinduced damage and it can be used in online inspection conveniently.
Precise measurement of the laser-induced damage threshold can be used to effectively evaluate the laser damage resistance of optical thin films. The determination of laser-induced damage threshold is dependent on the criteria to judge whether damage happens to the optical thin film or not. A measurement system with He-Ne laser scattered light was set up to detect the laser-induced damage threshold of optical thin films. The damage level of thin films was judged by measuring the variation of He-Ne laser scattered light energy at the same point on a sample. The damage threshold measurement for the diamond-like carbon films (DLC) and HfO2/SiO2 reflective coatings was performed. The measured result was compared with that of plasma spark method. Both of them have a preferable consistency. The analysis shows that the He-Ne laser scattering measurement system can be used effectively to determine laserinduced damage and it can be used in online inspection conveniently.
2008, 29(1): 136-140.
Abstract:
The quality check of the prism is very important for the measurement of optics. An accurate measurement scheme is proposed for testing the error of cone prisms with Hartmann wavefront sensor. The measurement theory was discussed, the reconstruction of the wavefront reflected from a cone prism was studied, and the relation between the wavefront characteristics and the errors of a cone prism was given. The feasibility of the method was verified in the experiment.
The quality check of the prism is very important for the measurement of optics. An accurate measurement scheme is proposed for testing the error of cone prisms with Hartmann wavefront sensor. The measurement theory was discussed, the reconstruction of the wavefront reflected from a cone prism was studied, and the relation between the wavefront characteristics and the errors of a cone prism was given. The feasibility of the method was verified in the experiment.
2008, 29(1): 141-143.
Abstract:
In measurement for laser power and energy，the ambient temperature of military laser measurement in field is different from the laboratory temperature. The sensitivity of laser energy meter sensor is relative to ambient temperature. If laser energy meter is not calibrated for temperature sensitivity, the measurement results will be affected greatly. Aiming at the problem, the paper proposes a new method in which the laser energy meter is put in temperature control box and the output pulsed laser is divided into two beams after beam splitter. The transmitted beam is accepted by standard energy meter or field laser meter, the reflected beam is accepted by reference energy meter and the calibration is done in temperature range of -50℃～70℃. The principle is verified by experiments and the results are analyzed. The function of sensitivity coefficient relative to temperature, which enables the accurate measurement of energy meter under nonstandard scenario. It provides a new reliable method for the study of calibration technology in field for laser energy meter.
In measurement for laser power and energy，the ambient temperature of military laser measurement in field is different from the laboratory temperature. The sensitivity of laser energy meter sensor is relative to ambient temperature. If laser energy meter is not calibrated for temperature sensitivity, the measurement results will be affected greatly. Aiming at the problem, the paper proposes a new method in which the laser energy meter is put in temperature control box and the output pulsed laser is divided into two beams after beam splitter. The transmitted beam is accepted by standard energy meter or field laser meter, the reflected beam is accepted by reference energy meter and the calibration is done in temperature range of -50℃～70℃. The principle is verified by experiments and the results are analyzed. The function of sensitivity coefficient relative to temperature, which enables the accurate measurement of energy meter under nonstandard scenario. It provides a new reliable method for the study of calibration technology in field for laser energy meter.
2008, 29(1): 144-151.
Abstract:
The optical wave transmission was studied with plane wave passing through the rough surface of layered medium. The scattering coefficient formulae of the transmitted light wave under different polarization states was derived with the perturbation method. The natural rough surface of layered medium was simulated with Gaussian rough surface. The calculation formulae for the transmission coefficient of the plane wave incidence to Gaussian rough surface of the layered medium was derived in combination with the power spectrum of Gaussian rough surface. The variation curves of HH polarization transmission coefficient with the scattering angle of transmission wave were obtained by numerical calculation. The influence of the dielectric constant of substrate medium, the dielectric constant and thickness of intermediate medium, rough surface parameters, and wavelength of incident optical wave on the transmission coefficient was discussed. The numerical results show that such influence is very complex.
The optical wave transmission was studied with plane wave passing through the rough surface of layered medium. The scattering coefficient formulae of the transmitted light wave under different polarization states was derived with the perturbation method. The natural rough surface of layered medium was simulated with Gaussian rough surface. The calculation formulae for the transmission coefficient of the plane wave incidence to Gaussian rough surface of the layered medium was derived in combination with the power spectrum of Gaussian rough surface. The variation curves of HH polarization transmission coefficient with the scattering angle of transmission wave were obtained by numerical calculation. The influence of the dielectric constant of substrate medium, the dielectric constant and thickness of intermediate medium, rough surface parameters, and wavelength of incident optical wave on the transmission coefficient was discussed. The numerical results show that such influence is very complex.
2008, 29(1): 152-155.
Abstract:
The self-imaging in spatial-frequency domain and its forming process are discussed, based on Weigner transform and distribution functions. A complete explanation for Talbot and Montgomery effect is presented by studying the optical path difference of each diffraction spectral component formed in the process of imaging. The theoretical basis, which can explain the self-imaging phenomenon with Yang′s double-slit interference, was acquired. It is found that the selfimaging of a periodic object results from the same phase coherent overlap of various diffraction spectral components, whose space in object plane is twice the period and optical path difference is the square of integral multiple of wavelength. Montgomery effect is a result of the same phase coherent overlap of various diffraction spectrum components, which have a distance of parabolic relationship in the object plane and their optical path difference is the integral multiple of wavelength.
The self-imaging in spatial-frequency domain and its forming process are discussed, based on Weigner transform and distribution functions. A complete explanation for Talbot and Montgomery effect is presented by studying the optical path difference of each diffraction spectral component formed in the process of imaging. The theoretical basis, which can explain the self-imaging phenomenon with Yang′s double-slit interference, was acquired. It is found that the selfimaging of a periodic object results from the same phase coherent overlap of various diffraction spectral components, whose space in object plane is twice the period and optical path difference is the square of integral multiple of wavelength. Montgomery effect is a result of the same phase coherent overlap of various diffraction spectrum components, which have a distance of parabolic relationship in the object plane and their optical path difference is the integral multiple of wavelength.
2008, 29(1): 156-159.
Abstract:
The parameter identificator and synchronization controller were designed to synchronize the uncertain chaotic systems with diverse structures. Taking the single-mode laser Lorenz system and Genesio system as examples, the method was proved effective and feasible. The Lyapunov function was deduced based on Lyapunov stability theory, and the structures of the identificator and the controller were presented. The simulation results show that all the state variables of the Genesio system can be synchronized with those in the uncertain Lorenz system by only one controller, the error signals approach to zero smoothly and quickly, and the synchronization between different chaotic systems is realized. All the parameters of the unknown Lorenz system can be identified.
The parameter identificator and synchronization controller were designed to synchronize the uncertain chaotic systems with diverse structures. Taking the single-mode laser Lorenz system and Genesio system as examples, the method was proved effective and feasible. The Lyapunov function was deduced based on Lyapunov stability theory, and the structures of the identificator and the controller were presented. The simulation results show that all the state variables of the Genesio system can be synchronized with those in the uncertain Lorenz system by only one controller, the error signals approach to zero smoothly and quickly, and the synchronization between different chaotic systems is realized. All the parameters of the unknown Lorenz system can be identified.
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