2012 Vol. 5, No. 6
Several kinds of radiometers on different spacecrafts for Total Solar Irradiance(TSI) measurements are briefly described in this paper, and their structures, instrument characteristics, principles, and operation are introduced. It shows that the TSIs for most of spaceborne radiometers are measured using the principle of electrical calibration, and the cavity detectors are taken as sensors for the TSI. The influence of sun-pointing manner on measurement accuracy of TSI is also discussed for the spaceborne radiometers. Finally, based on the history and experiences of past space missions, the future development of spaceborne radiometers with high accuracy for measuring TSI is discussed.
Several kinds of spectral calibration technologies are introduced in detail, including the spectrum lamp spectral calibration, mono-chromator spectral calibration, tunable laser spectral calibration, and the gas cell spectral calibration. The experimental principle, experimental methods and technical characteristics of different spectral calibration technologies are described by analyzing and comparing foreign high spectral remote sensors for trace gases. Based on the characteristics of ultra-high resolution spectral calibration for atmospheric remote sensors, it points out that the bandwidth of calibration equipment should reach the level of 0.001 nm. It also suggests that the calibration method of improving optimization algorithm and comprehensive calibration methods should be considered to ensure the high spectral calibration accuracy of high spectral remote detectors for trace gases.
This paper introduces a new zoom lens technique that is varifocal-liquid technique. First of all, it reviews and summarizes the domestic and foreign scientific achievements on the varifocal-liquid techniques, and gives the basic principle, realization forms and the classification of liquid lenses. Then, the paper evaluates the excellent performance of the liquid lenses and their influences on optical fields, especially the revolutionary change brought by varifocal-liquid technique. Finally, for the development status and application engineering situation, it analyzes the urgency problems unsolved in varifocal-liquid technique. Finally, and it points out that the investigation and development of varifocal-liquid techniques should focus on the mechanism research to eliminate the effects of temperature field and gravity field on the performance of liquid lenses, the design of off-axis system and asymmetric system and further promoting the practical applications of the liquid lenses.
As the imaging quality of a three line array mapping camera can be reduced by stray light from different optical systems, the effect of the stray light is analyzed according to the result of optical design and a suppression method is put forward to reduce stray light based on the analysis and calculation of the stray light energy, the stray light irradiance on an image plane and the stray light coefficients at the entrance of camera. The stray light models of a three line array mapping camera are built and analyzed by using the software Light-Tools, and the obtained stray light coefficient of each system is less than 5%. Finally, a pratical experiment to test the stray light coefficient is performed by the surface source method and the tested result proves the correctness of the stray light analyzing and the feasibility of the stray light suppression methods.
To lighten the weight of a lunar-based Extreme Ultraviolet(EUV) camera and to ensure the function of the collimation frame structure of the EUV camera under the conditions of the large level vibration caused by satellite launching, earth-moon orbit transfer, moon landing and the large temperature difference on the lunar surface, a collimation frame structure based on Carbon Fiber Reinforced Plastics(CFRP) is designed. Firstly, different collimation frames are designed based on metal materials and the CFRP, and the superiority of the collimation frame based on the CFRP is verified by finite element analysis. Finally, the experiments on temperatures and mechanics are performed, and the experiment results show that CFRP collimation frame has a lighter weight and its stiffness and thermal stability meet the requirements of environmental adaptation.
In order to meet the practical requirement of airborne infrared searching and tracking systems, a dual Field-of-View(FOV) middle wave(MW) infrared optical system is designed based on the MW cooled detector with 320 pixel?250 pixel and a staring focal plane array. The system adopts the secondary imaging structure and a shield is installed in the first image surface station to reduce the stray light effect. The design results show that the system has a 100% cold shield efficiency; F number of the system keeps a constant as 4 and the image surface remains stable when only one piece of the optical lens is moved to switch the focus length between 800 mm and 400 mm; the field curvature and the distortion are less than 0.04 mm and 2.5%, respectively, and the MTF is more than 0.5 at 16 lp/mm. Obtained results demonstrate that the image quality meets the operational requirement.
On the basis of the theoretical thermal optical analysis of off-axis three-mirror systems, the image quality of a space remote sensing optical system in different thermal environments was tested by using a thermal optical experiment. After the actually measured temperature was input into finite element model, the surface aberrations of mirrors with temperature gradients were obtained using finite element analysis software, and the surfaces with aberrations were fitted with the Zernike Polynomials. Then, Zernike coefficients were input into the optical design software, and the imaging qualities of system with difference temperature gradients were analyzed. Finally, the experimental results were compared. It shows that the theoretical analysis results are in agreement with the measured results, proving that the analysis is correct. Measured Modulation Transfer Functions(MTF) at Nquist frequency are 0.247 at 18 ℃ and 0.221-0.254 between 14-21 ℃, which meet the requirement of image quality.
The superiority of an optical vertebra transmitting device is introduced. The main factors that impact the coupling efficiency of the optical vertebra transmitting device are analyzed, and the theoretical model error curves which impact the coupling efficiency of the optical vertebra transmitting device are gained. By taking the reflection loss of an optical vertebra end face and the fiber radiation loss as the main error sources, the coupling efficiency of optical vertebra transmitting device and the impact of errors on the coupling efficiency are tested, and a calibration method using the split ratio to measure the coupling efficiency of the transmitting device is proposed; furthermore, the impact of the changing of laser output on pulse energy measuring is eliminated. Based on the testing data, the impact curve of error on the coupling efficiency is fited, then the accuracy of the theoretical model is verified by comparison with the theoretical error curve, meanwhile the coupling efficiency of the coupling device is measured to be 70.26%. Under the condition that the laser beam incident angle error is less than 5? and the fiber is swung under the tolerance in the fiber bending extent, the effect of total error on the coupling efficiency is less than 10%, which meets the allowable error of the actual project. The coupling device has been applied to practical engineering.
The location, structure, working principle and the assembling method of a reflex light-tube in a photoelectric pointing system are introduced, meanwhile the effects of installation error and assembling error of the reflex light-tube between two plane mirrors on the accuracy of azimuth transfer are analyzed. Matlab software is used to compute and draw the statistic histograms of the azimuth transfer error and the elevation error, and the results provide a guidance for the assembling reflex light-tube. According to the results from calculation and analysis, the main factor affecting azimuth transfer error of reflex light-tube is the assembling error between the two plane mirrors in the reflex light-tube. As long as the assemble error between the two plane mirrors satisfies the technical requirements of azimuth error4 and elevation error0.5', the azimuth transfer error of the reflex light-tube can be 10 even the installation error extrema in three directions of the reflex light-tube reach 15.
A centerline camera subsystem is designed for the mother-ship recovery television surveillance system. An Electron Multiplying Charge-coupled Device(EMCCD)-based Electrical-Optical(EO) imager is proposed according to the requirements for illumination principle, imaging contrast and resolution. The stability of a gyro-stabilized platform and the accuracy of a centerline camera are analyzed, and several imaging processing methods are discussed to solve the problems of position and inclination angles. It is found that the EO system based on Andor Ixon EMCCD with a diameter of 40 mm can fulfill the optical requirements for the centerline camera. The F/2 optical system based on a petzval show its MTF to be close to the diffraction limit. The stability and accuracy status-quo gyro-stabilized platform is enough for the surveillance system. The centroid algorithm and edge operator imaging processing method are proposed to calculate the altitude, latitude and inclination. The designed system is capable of performing surveillance with 24-hours a day, which is suitable for aircraft landing on carriers.
The optical system of a solar simulator used for a transient calorimeter calibration system is designed, which comprises a Xe arc, an ellipsoidal specular reflector and a channel optical integrator. The design criteria and limitations of the ellipsoidal specular reflector are introduced, and the work principle and spatial uniformity of the integrator are also analyzed. Then, based on the sizes of receiving surface and installation space, the system design is optimized and simulated. The simulation results show when the amplification factor and the length of the integrator are set to be 4.5 and 8.5 mm respectively, the received average flux will be 4 250 sun constants with a radiation uniformity below 3% for a 7 000 W Xe arc lamp, and 2980 sun constants with the same radiation unformity for a 5 000 W arc lamp. Both of them can meet the operating requirements of the transient calorimeter calibration.
This paper introduces the composition and operational principle of solar simulators. Based on the extence concept of non-imaging optics, the whole system including an illumination system and a projection imaging system are matched, and the energy transfer in the whole system is analysed on the basis of Lagrange invarian. The best matching relationship of relative aperture 1/4 among the ellipsoid condenser, optical integrator and the collimated object lens are obtained and satisfies the pupil connected principle. This calculated value of Lagrange invariant is 0.45, which verifies that the Lagrange invariant is conserved from an object surface to an image surface. So the optical energy of the optical system is used effectively.
Based on phase diversity technology, this paper designs an Offner optical system for image restoration and optical test of wavefront errors. The Offner optical system uses an on-axis parabolic mirror as Offner mirror, and a high speed CCD camera and a Shack-Hartmann wavefront sensor as the receivers to eliminate the chromatic aberration brought by the polychrome light source of the refractive system during image restoration. The system has a simple configuration with the wavefront error(RMS) less than /50(=632.8 nm). By using the system to perform image restoration experiment for a resolution plate and a fiber source, the resolution of restorated image is improved by 19%. In addition, wavefront error test are performed with the Offner optical system using the phase diversity algorithm, and the result demonstrates that the wavefront sensor difference between phase diversity and Shack-Hartmann is 5%, which proves that it is able to perform optical wavefront test with this Offner optical system.
On the characteristics of the interpolation, gradient-based and Newton-Rapshon algorithms used in the sub-pixel process in the laser speckle technology, the same laser speckle pattern was calculated one by one with the three sub-pixel algorithms under the drying process of the magnet fluid, and the mean bias errors and the standard deviation curves in a sub-pixel scale were worked out. The characteristics of the three algorithms to process the laser speckle pattern given by the mean bias error and standard deviation were discussed and the calculation accuracy, stability and calculation consumption were compared. It is shown that the precision and stability of the gradient-based algorithm is higher in the small deformation within the sub-pixel displacement measurement. The computing efficiency of the gradient-based algorithm is approximately nine times faster than that of Newton-Rapshon method. Therefore, it is more efficient to take advantage of the gradient-based algorithm to calculate the laser speckle in the small deformation and the sub-pixel displacement measurement.
For the measurements of temporal and spatial distribution parameters of high energy laser beams, a synthetic measurement of calorimetric and photoelectric method is studied. The data fuse of two kinds of sensors is achieved with a real-time scaling technique. Then, a set of compound measurement system is developed for measuring the large caliber laser beams. The system is mainly composed of 256 calorimetric detectors, 120 photoelectric detectors, multi-channel data sampling modules and one central processing computer. The total energy of the laser beam is precisely measured with the calorimetric detectors, and the high temporal and spatial resolution distribution is given with the photoelectric detectors. With the merits of accurate energy and the high temporal resolution of two kinds of sensors, the compound system can be used for absolute measurement of the far-field temporal and spatial distribution of high energy laser beams.
The theoretical mode and structure composition of a fiber laser are introduced in this paper, and a double-clad Yb3+-doped quasi-continuous wave fiber laser system is set up by using 976 nm LD as pumped source. A square wave generator circuit for the laser pulse power source is developed, which can offer a repetition frequency below 1 000 Hz, pulse adjustable width between 10 s and 50 ms and duty ratio under 50% in a pulse mode. The characteristics and energy level system of the 11 m Yb3+ doped double-clad fiber laser are researched, and its ouput characteristics are measured. The results show that the highest output power is 2.67 W at pulse width of 10 ms and repetition frequency of 50 Hz when the maximum pump power is 8.12 W.
A new method combining relative measurement and absolute measurement is proposed to measure the transmittance characteristics of far-field beam quality of TEA CO2 lasers, and the intensity distribution for a 2 kW pulsed TEA CO2 laser in the distance of 500 m is obtained. The measurement results are discussed and analyzed. The experimental results show that the measurement is convenient and precise, and the influence of atmospheric turbulence is also taken into consideration. Flat top, fragmentation and furthermore side lobe appear in the intensity distribution. Measured by this method, the transmission rate of atmosphere is 81.5%, the maximum intensity is 1.59 W/cm2 and the divergence angle of cross direction is up to 0.64 mrad, which agree with the theoretical results. It is a very important reference for evaluating the effectiveness and optimization design of laser systems.
Ultraviolet curable material SU-8 2005 and thermal crosslinked polymer Methyl Methacrylatel Glycidyl Methacrylate [P(MMA-GMA)] are used as the core and the cladding layer materials, respectively, and a novel high-order Bragg waveguide grating filter with a thickness of 5 m, a width of 9 m and a grating height of 4 m is successfully designed and fabricated by direct photolithography technique. The characteristic parameters including resonance wavelength and transmissivity are carefully simulated. The performance parameters of fabricated device are measured to obtain the resonance wavelength of 1 550.4 nm, the extinction ratio of 23 dB and the 3-dB bandwidth of 2 nm.