2010 Vol. 3, No. 2
Atomic coherence is the result of interaction between light and materials, which leads to many important physical phenomenon. Currently, most experimental researches on atomic coherence are reported in atomic gases. Compared with atomic gases, the related experimental researches in solid materials have more practical applications. This paper introduces the recent research progress of atomic coherence in solid-state materials in detail, including the Electromagnetically Induced Transparency(EIT) in solid materials, light velocity reduction and coherent storage, controllable eraser of optical storage information, all-optical route based on optical storage, optical velocity reduction and reversible storage of double light pulses and enhanced four-wave mixing based on atomic coherence, it also discusses its application to relative fields.
This paper introduces the development of solar simulation technology, gives design specifications of solar simulators, and then discusses the design and improvement of optical systems of solar simulators in detail. Several design methods of the condenser system are proposed, especially, a compound high-order aspheric surface condenser system and a non-coaxial ellipsoidal mirror are presented to raise the concentration efficiency of condensers and improve the irradiance distribution of the second focal plane. As the design of optical integrators is based on the Gaussian optical theory and its optimization is guided by the aberration theory, it presents an effective empirical formula for optimum design of optical integrators. This paper also briefly analyzes the design of collimating systems and the transmittances of filters. Finally, the current problems existed in the process of development are summarized and several improved ideas are put forward.
Image Motion Compensation(IMC) has been widely used in aerospace cameras to improve the imaging quality and the resolution of cameras. In this paper, the principle of IMC is analyzed and several kinds of IMC technologies used at home and abroad are introduced, such as optical IMC, mechanical IMC, integrate IMC, digital IMC. Then some common methods including parallel-slit method, scan and correlation method, heterodyne method, optical path difference method, direct calculation method are given to obtain an important parameter, speed-altitude ratio. Finally, this paper discusses the developing trend for digital IMC, presents the digital, real-time and miniaturization of measuring speed-altitude ratio and brings forward a new idea for measuring speed-altitude ratio by combining an array CCD with a high-performance microprocessor.
Based on the two-level and multi-level models, the AC Stark shift of the 5S1/2 and 5P3/2 states of 87Rb atoms in an Optical Dipole Trap(ODT) formed by a strongly-focused single Gaussian laser beam is analyzed and calculated. For performance of molasses cooling of 87Rb atoms in the Far-off-resonance Trap(FORT) by 852 nm Gaussian laser beam, the AC Stark shift of 5S1/2F=2-5P3/2F'=3 cycling transition for cooling is also calculated, results show that the frequency shift has an important impact on the molasses cooling process. Furthermore, the AC Stark shift of 87Rb 5S1/2|F=2,|mF=2〉 and 5P3/2|F'=3,|mF=3〉 states versus the wavelength of the ODT laser is analyzed, which shows that there is no magic wavelength for 5S1/2-5P3/2 transition of 87Rb atoms in the red-off-resonance condition.
In order to detect the function, performance and reliability of active thermal control system of a space camera, a simulation testing system to detect the active thermal control system was designed. The thermal-net mathematical model to calculate the temperature field of camera was established based on the basic law of heat transfer, orbital theory of spacecraft and the thermal control strategy, so that the active thermal control circuit could work in a simulated thermal space environment continuously, and the closed-loop testing of the active thermal control system could be realized. A method of two digital potentiometers in series was used to simulate the trend of temperature sensors, and the largest value of resistance achieves 100 kΩ and the measuring accuracy is 10 Ω. These results show that the simulation system meets the demands for total resistance and the rate of the resistance changes in design and achieves the simulated detection of the active thermal control circuit.
On the basis of technologies of virtual instruments and a PXI bus, a measurement and control system including its hardware buildup and software realization in LabVIEW was designed to measure and control multicenter physical parameters in a synchronization method in a space environment test. By using National Instrument(NI) multicenter data acquisition(DAQ) devices, the system has the functions of measuring and controlling parameter setting, data acquisition and processing, data and chart displaying, signal processing and analyzing and remote communication etc. It was successfully used in a thermal balance test of space camera subsystem to measure and control the temperatures of 36 thermistors and 14 thermocouples, and the experimental results show that it can meet the needs of an automatic temperature control accuracy in 0.5 ℃ and measuring accuracy in 0.15 ℃. As compared with traditional text languages, the system design economizes much time and can be applied in other related experiments and developments further. The designing method provides some references for the designs of other measurement and control systems.
The automatic damage detection system for a satellite solar array was firstly developed in China, and its detection theory, structure and design of detection system and the results of on-site trial were introduced. By using a unique lighting system, the image of the salar array was focused clearly onto a CCD sensor via an optical system, then the signals were multiamplified and A/D converted to store in a computer system. An imaging probe automatically scans the whole array and keeps the image clear through the control of a distance sensor. The customized system control and detection software were used to process every battery image, then testing results were shown on a table to offer the location of the damaged battery, damage types and damage degree etc. An on-site test shows that detection rate of the system is over 98.5% and detection speed is 20 batteries per minute, which meets the requirements of fast, accurate and automatic detection of the solar array.
The development of flexure hinges with large deflection, low stress, small parasitic center shift has always been a difficult problem. On the basis of some foreign flexure hinges, this paper designed a new kind of flexure hinge by using a V shape structure, symmetric layout and the superposition principle. The concept design theory of this flexure hinge was analyzed, and a mathematic model was established to analyze its performance. Analyzed results show that the length of flexure part for the hinge has increased and its parasitic center shift and maximal stress have decreased. Finite element method indicates that its maximal deflection is about 16°, maximal parasitic center shift is 3.557 μm, and maximal stress is 499.8 MPa, respectively, which meets the requirement of design target and the results prove that this flexure hinge has a good quality in practices.
The theory of temperature measurement by infrared imagers is introduced and the factors that influence the accuracy of infrared temperature measurement are analyzed. The error curves of temperature measurement at different surface emissivities are given. Using theoretical analysis, it is shown that the higher the surface emissivity of an object is, the more accurate the measuring accuracy of imager is. By changing the setting of surface emissivity, the corresponding total radiance luminance to surface emissivity is calculated. Analysing the results, the conclusion indicates that TP8 long wave thermal infrared imager can measure the temperature accurately when the surface emissivity is above 0.5. Finally, three materials whose surface emissivity is 0.96, 0.93 or 0.3 are measured, respectively, and the result shows that a higher surface emissivity leads to a better temperature measuring accuracy.
On the basis of characteristics of optical systems of Offner spectral imagers, the material choices of every parts, structure design of mirrors and frames in the imagers were investigated, then the structure design of a compact Offner spectral imaging system was achieved and its 3D model was established. In order to prove the reasonability of the structure, the 3D model was analysed by finite element method. The analysis results indicate that the first natural frequency of the structure is 362 Hz, which is higher than 120 Hz requested by the system. Furthermore, the analysis results of weight and temperature indicate that the RMS of surface figure, distances, centrifugal axes and the deflection of angle in every important parts all meet the requirements of the system tolerance. These results validate the rationality of structure of the compact Offner spectral imaging system.
On the basis of a cool 320×240 detector with staring focal plane array, a set of middle infrared continuous zoom system is designed for airborne optoelectronic detection and tracking apparatus. The system is composed of a zoom system, a secondary imaging system, and two reflectors. The method of pupil-join for a secondary imaging system is introduced and the schematic diagram and its parameters are given by using an optical design software, then the image quality and Narcissus effect are analyzed. The design results prove that the system worked at 3-5 μm has achieved the zoom of 10 mm to 180 mm, large zoom ratio of 18× and the F number of 3. The system can offer a high resolution, heat sensibility and excellent images, and its cold shield efficiency is 100%. The compact system meets the design requirements.
To improve the analysis accuracy for the optical mechanical structure of a optical system, a nonlinear analysis method is introduced and then a nonlinear Finite Element(FE)analysis is applied to analysis of the mechanical model of a primary mirror subassembly. The main source for structural nonlinearity is summarized, and a FE model for the primary mirror subassembly of a collimator is established on the basis of contact theory. The mirror response based on bolt contact and the mirror deviation based on gravity and temperature loads are analyzed by contact nonlinear analysis method. Using a practical mesuring result, the linear and nonlinear methods are compared, and it is included that the contact nonlinear analysis indeed reduces the analysis error. Therefore, nonlinear analysis can improve the analysis accuracy and obtain the results which are close to that in real system of engineering analysis.
The basic principles of infrared imaging simulation was introduced, and a method for generating infrared images from visible images based on Vega was discussed. By the proposed method, the Creator was used to establish a 3D gemetric model and to realize a texture mapping, then the Texture Material Mapper(TMM) was applied to modelling for infrared materials. Furthermore, by using the Mat software, the atmospheric attenuation was calculated. A characteristic model of sensor was established by SensorWorks and infrared images were generated with photoelectric conversions. Finally, Apache AH6 helicopter was used in infrared simulation in this paper. The results show that the module established by Vega sensor has advantages in effective modeling, low costs, and the method is suitable for engineering practice.
This paper presents an effective interpolation restoration algorithm for color images in Bayer format to reduce the computational complexity and improve its real time property. Based on the characteristics of human visual system in the interpolation process, the more accurate brightness information and edge information of the image can be obtained. Owing to edge information, more accurate values of|R, G, B can be recovered. The final solution of the algorithm is a series sparse linear filters with sizes of 5 × 5. It has a lower complexity and can be processed easily in the embedded processors of computers in real time. Experiments show that the Peak Signal to Noise Ratio(PSNR) of this algorithm is higher 4-6 db than that of the common bilinear algorithm. Furthermore, it effectively reduces the sawtooth phenomenon occurred in the interpolation algorithm and shows that its recover ability and real time property is superior to that of the traditional bilinear interpolation.
In order to reduce the mount of image data, enhance the speed of image transmission and to realize the high-speed transmission of aerial images, a high-speed and feasible method for image transmission was researched. On the basis of the Picture Transfer Protocol(PTP), an image transmission system of aerial digital camera was presented by using the JPEG image compression algorithm and the multi-threaded transfer mode of file stream. The design scheme of the system was introduced and its feasibility was proved. Experiment results demonstrate that the image average transfer rate is 53.641 Mb/s and error rate is 0.00%, which shows that this system not only guarantees a good data primitiveness and prevents data loss, but also reduces the data path blockage effectively.
A simulation train method based on digital image injection was presented to complete the training task of capturing and tracking target and to build the target environment. By simulating the target flight path, the output values of an encoder were received and calculated in real time, a comprehensive treatment with the equations of target motion was completed, and the target location information in images was worked out. Then, the digital image was injected into a digital image processing system according to the format of infrared images after synthesizing the target into the background. This method can simply and conveniently complete the tracking tasks in manual and automatic methods without using the infrared cameras, and can significantly reduce training costs. The method has been successfully used in the simulation training system of a photoelectric tracking and pointing apparatus.