2015 Vol. 36, No. 5
A high zoom ratio optical system with f=10 mm~500 mm was designed. The initial structure and reasonable Gauss solution were given by Gauss optical computing based on positive mechanical compensation principle. Two novel aspheric surfaces were introduced in this system, which could provide more degrees of freedom for optical design, correct aberration in optical systems effectively, as well as the complexity of system, and this is advantageous for achieving high zoom ratio system. The second order spectrum from telephoto was corrected by a group of double-layer harmonic diffractive element, that could reduce the number of sheets of lens and make the system more compact. The curves of zoom group and the compensating group were simulated, and the modulation transfer function(MTF) curve was analyzed in the case of 10mm to 500mm focal length. From the above we can see that, the system can satisfy the change regulation of the mechanical compensation cam curve, the curve is smooth, and a smooth zoom is achieved. When Nyquist frequency is 50 lp/mm, the MTF is greater than 0.6, and high quality image is achieved.
The running speed and dynamic range of existing correlators cannot meet the requirements of photon correlation spectroscopy. The structures of linear and multi-tau correlator were analyzed in order to overcome this disadvantage. An optimized correlator which included the fast channels by using multi-tau correlator and the slow channels by using linear correlator was proposed based on the advantages of both correlators. Therefore, a fast photon correlator with high dynamic range was designed by the optimized structure. Experimental data show that the sampling time of the fast photon correlator can be set to 10ns, the maximal dynamic range is 1.11012, and the baseline error is 0.095% by using modified normalization method.
In order to meet the testing need of rad level stabilization accuracy of high-precision EO stabilized sighting system in future,a method for testing the stabilization precision based on interferometer was proposed. According to the influence of the optical path difference of the two beams with the same source in the Twyman-Green interferometer on the interference fringe,the slight change of the interference fringe was observed utilizing the charge coupled device (CCD),as a result, the measurement of the stabilization precision was realized. By utilizing this measuring method, the aiming precision of the fast steering mirror (FSM) and the stabilized precision of a certain type of EO stabilized product were measured . Results show that the measurement precision can achieve 0.2 rad with our method.
In order to ensure the image clarity of the high-definition surveillance cameras in the large-range zooming process, a new zoom tracking method was presented. In this method, confidence interval was constructed by geometric method according to several zoom trace curves which were collected in advance; Zoom tracking curve was determined by the center position of confidence interval, and its dynamically adjusted with the adaptively adjusted confidence interval. This method was realized in an 18 digital high-definition surveillance camera. Experimental results indicate that the average bias of the focus motors position relative to its best position is less than 0.018 75 mm and the average time of zooming from wide-angle to tel-angle is 4.1 s.
Based on the Ritchey-Chretien(R-C) system, a refractive/reflective system with a Margin-like mirror and 3 correcting lenses in front of the focal plane was designed with the help of Zemax software. It has a focal length of 3000mm, F number of 8, waveband of 450nm~900nm, and the field of view reaches 1. It is shown that the value of modulation transfer function(MTF) is higher than 0.55 at 50 lp/mm, the image quality reaches the diffraction limit,and the distortion is less than 0.022%. An R-C optical system is made up of the aspheric mirror of the Margin-like mirror and the primary mirror of the system without the spherical aberration and the coma aberration. The refractive surface of the Margin-like mirror shares the optical power of the secondary mirror, reducing the asphericity of the aspheric mirror. Results show that the Margin-like mirror can lessen the square asphericity of the secondary mirror from 4.356 to 1.940, and reduce the length of the system from 600 mm to 550 mm.
In order to acquire a more exact surface figure error result,the method about solving the Ritchey-Common test data was studied. Based on the existing mathematical model, a method which utilized the relationship between the system pupil coordinate and test flat mirror surface coordinate to recover the surface error condition was introduced. The effectiveness of this method was verified by simulation, the theoretical accuracy of this method was also analyzed. Comparing the test result with the result measured by interferometer directly, we can know the actual test accuracy of coordinates transforming method: the peak-valley(PV)value is better than 1/20 ,the root-mean-square (RMS) value is better than 1/100 , which can satisfy the high requirement of test. Even comparing to result of impact matrix method, the accuracy of PV and RMS can improve 0.013 ,0.0037 respectively .This indicates that the coordinate transforming method is more suitable for Ritchey-Common test.
In order to improve the accuracy of wavelength scanning of grating spectrometer, we designed a set of real-time feedback system for grating rotation situation and implemented the instrument with both high speed and high precision scanning. In the design of feedback structure, we applied the grating displacement measuring technology to feedback the displacement of the slider on sine bar, and utilized the computer for receiving and processing it . Contrast experiment shows that the instrument accuracy of wavelength scanning is 0.7 nm, after incorporating the feedback circuit, the wavelength scanning precision can reach 0.15 nm. Results indicate that after adding can the feedback structure of the grating rotation situation, the grating spectrometer satisfy the requirement of high precision scanning.
In order to realize the radiation detection of the full spectrum imaging spectrometer, a large aperture off-axis reflective solar simulator was designed, which can offer the natural sunlights irradiation under the laboratory conditions. The design of the optical system of the solar simulator was discussed in detail with the simulation and analysis by the Lighttools. According to the layout of the optical system and the thermal load distribution of the system, by using ICEPAK, the air cooling system was designed and tested. The results show that under the condition of satisfying the system cooling requirements,a 1.17 constant solar irradiation can be achieved by our solar simulator, the irradiation non uniformity in 200mm range is less than 1.61% and less than 3.28% in 400mm range.
In order to improve the temperature stability of long focal length zoom lens, the influence of temperature on the optical system was analyzed. By the simulation analysis of long zoom lens optical system for temperature in CODE V, it is found that the temperature has a great effect on the image quality of optical system. At first the initiative focusing compensation mode was adopted to compensate the temperature effect of the optical system. Although the image quality improved after compensation, the CCDs max frequency of modulation transfer function (MTF) is low, and the best image plane of every focal length of zoom system cannot parfocalize. By adopting the mechanical passive compensation and active focusing compensation to get the compensation of temperature, the optical system can realize good image quality within the required full temperature range, and the MTF is greater than 0.5 in short focus while greater than 0.25 in long focus. The focus length can be compensated, and the best image plane of each focal length can parfocalize and overlap with the CCD image plane.
Radiation gain acting as the main performance parameter of the ultraviolet(UV) image intensifier determines the comprehensive performance of it，so a test intensifier was designed to measure the radiation gain in UV image intensifier,whose test range was 200 nm~400 nm, and there were 6 (1/8,1/4,1/2,1,2and 3) fields of view (FOVs) for choice .Referring to the image intensifier brightness gain measurement device, the testing system of radiation gain in UV image intensifier was designed. Based on the testing principle and method, the test software was designed. By changing the voltage of micro channel plate,the cathode voltage and screen voltage, the UV image intensifier was measured. The test results indicate that the test curve changing trend coincides with the operation characteristics of the UV intensifier, the incident UV radiation intensity is 10-7W/cm2~10-11W/cm2,the minimum detecting intensity of radiometer was 10-11W/cm2,the minimum brightness detection threshold is 310-4cd/m2 and the test repeatability of radiation gain is better than 8%.
Color vision of spectral data after reducing dimension and redundancy was researched. The traditional mapping method, cutting or compressing data into the range between 0 and 1, can always lead to loss of the fusion image details. A novel fusion and vision algorithm of spectral data was presented, based on the shifting-mapping-evaluating-optimizing way within multi-section. The first 3 principal component values were achieved by principal component transform (PCT) of the spectral data cube, and assigned respectively to white-black, red-green and yellow-blue channels of opponent color space. The values of standard red-green-blue (sRGB) color space were transformed from opponent color space, and the sRGB values were divided into several sections, moved to the range of 0 to 1 and mapped to 8bit RGB digital code values. The single item evaluations of standard deviation, entropy, average gradient were calculated from 8bit RGB. The comprehensive evaluation values were got from all of the single item evaluation after finishing the process of moving, mapping and single item evaluation. The fusion image was mapped at the section with maximum comprehensive evaluation. The results show that the fusion image can ensure the images energy, information and definition, which is useful for manual distinguish and judge rapidly.
To improve the remote sensing image and multi-focus image fusion accuracy, combined with the non-sampling shearlets transform (NSST) which can capture the details of the image features, we proposed a image fusion method based on NSST and weighted area feature. Firstly this method uses nonsampling shearlets transform for source image to carry on multi-scale multi-direction decomposition to get low-frequency and high-frequency subbands.Then the improved gradient projection of non-negative matrix factorization(NMF) is used for the low-frequency sub-band coefficient,while the high frequency sub-band coefficient uses the fusion strategy combining the regional energy and variance of the weighted area. Finally, the non-sampling shearlets inverse transformation is used to get image fusion. The experimental results show that this method can well retain the useful information of multiple images from the aspect of subjective vision,and the comparison results are given with other fusion methods from the aspect of objective evaluation indexes such as entropy, mutual information and weighted edge information preservation values.
In order to rebuild the pressure distribution from the schlieren image of focused ultrasound field directly, relationship was presented firstly between the spatial distribution of sound pressure and the intensity of schlieren image getting by Zernike phase contrast system based on the acousto-optic effect. Then the real-time sound image of focused ultrasound was obtained by the schlieren system. Due to the physical property of schlieren system, the spatial sound pressure distribution of a concave spherical shell focused ultrasonic transducer could be reconstructed by using a back-projection reconstruction algorithm lastly. According to analysis，when the electric power is 12 W, the horizontal size of reconstruction focal region is 0.25 mm closest to the theoretical 0.15 mm and when the electric power is 30 W, the acoustic axis size of reconstruction focal region is 1.35 mm closest to the theoretical 1.4 mm. Results compared with the theoretical sound pressure distribution of the spherical shell transducer show that this method has certain feasibility for ultrasonic transducer measurement.
Aiming at the problem of the blurred direction detection of small-scale motion blurred image, a new algorithm for blurred direction detection was presented by analyzing the cause of detection error. Firstly, we refined the bright lines with median filter in the twice Fourier spectrum to eliminate the spectrum noise. Secondly, we chosen mid-value as a threshold to transform the spectrum to a binary image. And then we removed the cross bright line and bright speck to heighten the direction feature. Finally, we projected all bright spots onto the straight lines of all slopes through the center of the binary image, and calculated the maximum of projection to estimate the blurred direction. Furthermore,the effectiveness of the algorithm with the blue scale of degraded image varied from 3 pixels to 10 pixels was verified by simulation. Experiments demonstrate that the estimation accuracy of this method is higher than other methods in smallscale motion blurred image.
Object tracking using single feature often leads to a poor robustness. Aiming at this,an object tracking algorithm using multiple features fusion based on color and space information was presented. In order to enhance the important features, an adaptive method for choosing object color histogram was proposed to get an accurate color model of the object. Meanwhile, spatiograms were used to obtain spatial layout of these colors for the targets. These features were rationally fused in the framework of particle filter. The uncertainty measurement method was then introduced into features fusion to adjust the relative contributions of different features adaptively, and the robustness of the algorithm was significantly enhanced. Simulation experimental results show that the mean minimum location error of the proposed tracking algorithm is only 6.967 pixel,while that of the signal feature tracking algorithm and the traditional algorithm are 192.576 pixel and 199.464 pixel,respectively, which indicates that the proposed algorithm can track objects with better tracking accuracy and robustness.
Digital speckle correlation method has the advantages of low demand of the measurement environment, overall non-contact measure, however, the algorithm efficiency has been one of the bottlenecks limiting its development. The graphics processing unit (GPU) has the natural parallelism, GPU highperformance computing brings great efficiency on computer image processing. By programming with the compute unified device architecture (CUDA) platform, the GPU high-performance parallel processing was applied for the traditional digital speckle point-by-point search algorithm, cross search algorithm and genetic algorithm.Comparing with the traditional method, the experimental results show that the efficiency of these 3 methods improve by 20,8,31 times respectively for 150150 pixels speckle image, while by 183,33,44 times respectively for 500500 pixels speckle images and by 424,116,44 times respectively for 1 0001 000 pixels speckle images.
In order to improve the shortcoming of insufficient sampling of measured wavefront in traditional Hartmann-Shack wavefront sensor(HWS), the HartmannShack wavefront sensor and micro-scanning technology were analyzed, at the same time, the method of lens micro-scanning by raising the sampling rate in Hartmann-Shack wavefront sensor was proposed . The lens scanning device driven by PbZrTiO3 (PZT) was added before the microlens array,and the highresolution micro-scanning image was reconstructed for the spot distribution collected by the charge coupled device (CCD) . After the wavefront reconstruction of the rebuilt spot distribution, the sampling rate of measured wavefront was improved in Hartmann-Shack wavefront sensor. Comparison experiments verify that the method can raise the recovered accuracy of wavefront by 41%, and it can effectively increase the accuracy of wavefront detection in Hartmann-Shack wavefront sensor.
In terms of the calculation of absolute phase in conventional grating projection methods, the unwrapping algorithm is applied. Due to the demand upon spatial phase continuity from the unwrapping algorithm, it is not suitable for the measurement of objects with step-height. A multi-scale fringe projection measurement was put forward to tackle this problem, and the absolute phase of high-density fringe projection could be directly gained. Through the experiment upon the quadratic fitting curve of the high-density 64 periods fringes phase measurement, within the variation range [-201,201] of the absolute phase, the fitting standard deviation reaches the precision of 0.096 63 rad.
In order to accurately diagnose the shafting vibration characteristics,a method based on the principle of laser Doppler frequency shift was proposed to measure the rotation shaft bending vibration,torsional vibration and shaft rotation speed at the same time. Combining with the optical heterodyne technique and the reference light technology, the Doppler heterodyne interference light path was designed for separating the twist vibration,and the mathematical model of the measurement system was constructed.Moreover, the main factors were analyzed for affecting the laser Doppler bending torsional vibration measurement, the influence of various parameters on the measuring results were discussed and the corresponding measurement uncertainty was presented . In the confidence level of 95%, the uncertainty of the instantaneous speed is 0.079 r/min,and that of the bending vibration velocity component is 0.001 4 mm/s, which can meet the requirement of the rotating shaft vibration comprehensive measurement.
Aiming at the calibration problem of the binocular vision measurement system using a light pen, the theory about the calibration of camera intrinsic parameters, double-camera extrinsic parameters and measuring pen was discussed. At the same time, the whole calibration system based on LabVIEW was developed. The camera intrinsic parameters calibration wasachieved by using Zhang plane calibration method,while the double-camera extrinsic parameters calibration was achieved by the method based on standard length. Using the method combining the particle swarm optimization with the Levenberg-Marquard(LM) algorithm, the high-dimensional optimization target function was speeded up effectively. In the process of measuring pen calibration, a very convenient field calibration method based on least square was proposed. The calibration system could complete all the preparation work before the relevant measurement. It has high precision and practicability. Based on the calibration results of measurement system, the standard deviation of test result for the 25 mm diameter standard ceramic ball is 0.019 mm.
In order to solve the problem of high-precision measurement of aspheric mirror,we put forward the method of aspheric annular sub-aperture stitching testing by using Zygo interferometer.By moving the stay of the testing aspheric surface,the reference spherical waves produced by the inteferometer could match the different band areas of the testing aspheric surface with different curvature radii, each annulus was tested,then the whole aspheric surface testing could be completed.A hyperboloid reflector was tested with annular sub-aperture stitching, and a light path was set up to verify the stitching result using aberrationfree point method . The results show that the error is less than 1/20 (=632.8 nm).
In order to obtain the effect of ion source parameters on etching rate and surface roughness in the process of ion beam etching polishing.We used the microwave ion source as the etching ion source, took benzocyclobutene (BCB) as the object of study, and did the research of the effect of ion source parameters,including the energy and current density of ion beam, the quantity of oxygen and argon,on etching rate and surface roughness,and then obtained the relationship between the ion source parameters and the etching rate, roughness evolution.It turns out that in the process of ion beam energy increasing from 400eV to 800eV, the etching rate increases constantly, increasing from 3.2 nm/min to 16.6 nm/min; in the process of ion beam current density increasing from 15 mA to 35 mA, the etching rate increases constantly, increasing from 1.1 nm/min to 2.2 nm/min; in the process of quantity of oxygen increasing from 2 mL/min to 10 mL/min process, the etching rate increases but decreased a little at 8 mL/min.There are no big changes on surface roughness, can be at 1.8 nm or less.
In order to make the research status of diamond-like carbon (DLC) thin-films be well understood, the characteristics and applications of the DLC thin films were reviewed, and the preparation technologies were compared and analyzed, including the physical vapor deposition (PVD) methods and the chemical vapor deposition (CVD) methods. And the laser-induced damage properties and the methods to improve the laser-induce damage threshold of DLC films were discussed. The results show that the hardness and the residue stress of DLC films deposited by the physical vapor deposition methods can respectively reach to 40 GPa~80 GPa and 0.9 GPa~2.2 GPa, but the chemical vapor deposition methods has been less used because the deposition rate of DLC films decreases greatly introduced by the reaction gas. Moreover, some methods of the optimization of the electrical field intensity of film stack, the reasonable preparation technology, the laser conditioning, and the application of external electrical field can effectively improve the laser-induced damage threshold of DLC films, and the laser-induced damage threshold of DLC films can get 2.4 J/cm2 at present.
The two-dimensional(2D) metallic grating was introduced into the detector to improve the detection rate of Terahertz(THz) quantum well photodetector(QWP). The 2D metal grating simulation model of THz QWP was established by using the 3D finite-difference time-domain algorithm, the impact on the electric field strength of the 2D metal grating parameters of THz QWP was analyzed detailed. The results show that for the 6.27 THz (the corresponding wavelength is 47.847 m)incident light,the light electric field along the Z direction reaches its maximum and the grating coupling efficiency reached highest，when the grating parameters are taken as grating period P=10.5 m,dute cycle w= 5.755 m and grating layer thickness h=0.4 m
A wind turbine blade was tested for the full-field 3D deformations under biaxial static loads by making use of digital image correlation method. The results show that the 3D displacements of the wind turbine blade are well distributed while the strains are not. Among the three displacements, the out-of-plane displacement is much larger than the in-plane displacement. The flapwise displacements and edgewise displacements of the wind turbine blade induced by biaxial loads increase as the load increases. In the full field of the wind turbine blade, the flapwise displacements along the spanwise increase gradually, reaching maximum at the blade tip. The edgewise displacements of the wind turbine blade are all compressive displacements, the maximum of which are generated in the middle part of the blade. The spanwise displacements generated by biaxial loading are almost 0 in the region of 0~41% of the blade length. In the rest region of the blade, the tensive spanwise displacements are generated at the beginning of the loading, and compressive spanwise displacements are yielded as the load increases.
The optical design based on foci mapping ellipse flow-patch method has many advantages, such as clear geometric meaning, design flexibility and explicit method of optimization, but there is a drawback that the surface is not smooth. In order to sew up each ellipse flow-patch on the freeform reflector smoothly, the surface of reflector started from one point on the edge and a smooth ellipse flow-patch was built in the direction, then the discontinuity in the direction could be reduced by the energy adjusting method. The time consumption for the surface reconstruction from 40 000 ellipsoid pieces with this method is only about 2 min. The free-form surface cannot only ensure the energy distributed equally, but also improve the smoothness greatly.