2011 Vol. 4, No. 3
Applications and development of Carbon Fiber Composites(CFRPs) are overviewed in this paper. Firstly, the classification and mechanical properties of carbon fibers are described, and the characteristics of CFRPs are discussed. Then,the applications of CFRPs to cosmonautic fields at home and abroad are introduced, especially in satellite structures, carrier rockets, precision components and space mirrors. By taking some experiments for examples, it points out that the hydrothermal effect is main problem for CFRPs. Finally,some constructive ideas are put forward based on national conditions in the course of CFRP development.
Airborne 3D imaging lidar is a new technique to produce a angle-angle-distance, angle-angle-velocity 3D image by laser imaging. This article emphasizes the mechanism, functions and configurations of the airborne 3D imaging lidar systems as well as their applications which includes both the military and civil fields. Then, it states the current situation and developing directions of the airborne 3D imaging lidar system in detail. It summarizes that the airborne 3D imaging lidar in foreign couritries will make advances on long distance, high resolution, low power consume, real time and laser safety, However, the current domestic research is still at the laboratory stage, and there is still a gap compared with other foreign countries. Some of the key technologies need to be solved. Finally, by taking a 3D image lidar system from a user for an example, it analysizes the requrirements of the system for the range measurement, scanning structures, detectors and dada processing and display.
The development of solar thermal power generation technology is introduced. Five kinds of concentration systems, including parabolic trough concentrators, solar dishes, solar towers, lineal Fresnel concentrators and beam down concentrators, are presented. The optical structures, concentration principles, design methods and production process for the solar concentrators are described and the advantages and disadvantages of the different optical systems in the solar thermal power plant are commented. The discussion in this paper can provide references for design of solar thermal power plant concentration systems.
Varifocal optical system can meet the requirements of dynamic optical systems by changing optical parameters of optical components to adjust optical paths. This paper firstly introduces the fundamentals of varifocal optical system, and describes the design of the varifocal optical systems based on optical compensation and mechanical compensation. Then, it elaborates the type and structures of common focusing mechanisms and analyzes their advantages and disadvantages. It points out that along with the DSP control technology and stepping motor development, the varifocal optical mechanism has entered a new prospect. By making a reference to domestic and international engineering applications, the research shows that the numerical control technology based on stepping motors and DSP has an extensive forecast on varifocal optical mechanisms in the range equipment.
This paper describes the working principle of the dynamic star simulator based on a TFT-LCD and the calculation of the revised star angular distance error. A theodolite is used to measure the star point on the grid shown by the dynamic star simulator, then the position error correction factor of each star point is calculated based on the measured data. The correction coefficient of the star point on the grid is partitioned, and Matlab software is used for the curve fitting of each partition's revised correction coefficients to get the(azimuth or elevation) coordinate equations of the star position. The experimental result shows that the revised star angular distance error is less than 35, which meets the design requirements of the dynamic star simulator.
To measure total solar irradiance accurately, the solar irradiance absolute radiometer SIAR-3a with the ability of automatic solar tracking is designed and constructed. The principle and structure of the solar irradiance absolute radiometer SIAR-3a are presented in this paper and its control scheme for automatic double-axis solar tracking is proposed. The solar irradiance absolute radiometer SIAR-3a imposes electricity to calibrate the total solar irradiance, which is able to measure the total solar irradiance and follow the sun simultaneously. In the calibration experiments, the corresponding rms error limit of SIAR-3a amounts to 0.06% at the 3 level, which has been calibrated to World Radiometric Reference stored in World Radiation Centre(WRC) in Davos, Switzerland. The experiment results indicate that SIAR-3a works reliably and accurately.
According to elastic shell theory, several kinds of theoretical models of large aperture optical elements were established. A compensation method for the gravity deformation from a large aperture optical element was presented. With the method, the torque was applied at the edge of a lens frame to generate flexible deformation to offset the gravity deformation. An analysis model of the large aperture optical element with the frame was proposed, and it proves that the flexible deformation of optical element can effectively eliminate the influence of gravity deformation on the optical cell through optimizing the magnitude of force and the positions of support points.
In order to design the structures of large-aperture reference flat mirrors with high-precision, the shapes of a large-aperture reference flat mirror were studied under gravitational conditions. Firstly, the establishing method of the structure adhesive by finite element analysis was elaborated, and the finite element model of large-aperture reference flat mirror supported with adhered spots was established. Then, the influences of different number of adhered points and point distribution, different sizes of spots and support schemes on the shapes of large-aperture reference flat mirrors were researched. Finally, the structure for large-aperture flat mirror supported with adhered spots was designed. The experimental results indicate that by support scheme with 123 distributed and 5mm diameter adhered spots, the peak to valley(PV) value and RMS value of the reference surface is only 24.06 nm and 6.78 nm, respectively, which satisfies the requirement of shape precision of the large-aperture reference flat mirror.
Automatic lensmeter is an instrument for measuring optical parameters of glasses. For several universal problems on the small measurement range and poor accuracy of the automatic lensmeter, this paper developeds a instrument. It uses motor compensation principle to adjust the linear motion position of a partition board to implement the compensation, and changes the relation of the images and the object to achieve the focal power measurement accuracy and enlarge the measuring range. When a lens is placed in the optical system until the end of the adjustment process, the electrical components will receive the image and analyze the averaged calculation, which can get the parameters of the lens under test. After a system demonstration and testing, the prototype is used to successful measure some typical lenses. The results show that all lenses are in the range of error within 0.02 m-1. The measurement results fully meet the requirements of national metrological verification test.
A new image injection system was presented to realize the direct transmission of PC simulated images. Firstly, the system received a BMP file obtained by simulation for the measured data of the external field using PC though USB2.0. Then, a FPGA was used to control the buffer module consisting of two SDRAMs for the image cache, and the image was sent to the image acquisition card by Camera Link. Finally, the image was acquired by the image acquisition card and displayed on a monitor. The ping-pong operation was adopted for data cache to avoid the condition that the data couldn't be received continuously and valid data may be lost. Experiments show that the image injection system has advantages in well real time, vividly and high-speed features, and provides reliable data for optical equipment scanning and manipulator training.
In order to enhance the auto-focusing capability of a imaging system, a difference image extraction method is proposed. Meanwhile, a evaluation function based on wavelets and a region selecting technique using Particle Swarm Optimization(PSO) are given. The principle and superiority of the difference image extraction method are introduced. Then a selecting criterion and a searching method using PSO for region evaluation are described, and the parameters for wavelet based evaluation function are compared and optimized. Finally, emulation experiments are practiced to analyze the advantages and disadvantages of traditional and proposed methods. Results indicate that the proposed method can offer a higher resolution to the focusing curve due to the difference image extraction, new focusing window and focus evaluation. Moreover, it has improved the focusing speed by 170 ms and provided the focusing precision about 2.3 m. Furthermore, its focusing effects are always satisfactory with different initial positions.
In order to meet the special requirements of infrared military equipment, an infrared double waveband filter film system was designed according to the theory of thin film and an infrared dual-band filter membrane with a high reflection at 1 064 nm and a high antireflection in 3~5 m was produced on a multi-spectral ZnS substrate by adjusting process parameters and using electron beam vacuum deposition. With ion bombardment of low energy and vacuum annealing, the anti-damage threshold of thin film was improved. Furthermore, the stress between the film layer and the substrate was reduced to 51 MPa from 122 MPa measured by the BGS 6341 stress tester with gradient method. This film meets the requirements of infrared military equipment.
For the energy loss of laser transmitting, an anti-reflection film and a high anti laser reflection film were designed and prepared according to the theory of optical thin film. Coating materials of laser films, coating design, deposition techniques and ion assisted deposition parameters were researched in detail. Results shows that the reflectance of the antireflectance coating is less than 0.2% and the average reflectance of the high reflectance film is higher than 99.7% when the laser incidence is 25~65. Furthermore, the experimental tests on 50 m optical fiber and K9 glass before and after coatings indicate that the average power of optical fiber has increased by 5% and the reflective power of the K9 glass has improve to 99.85%. Moreover, the preparation of optical films of the fiber laser effectively raises the laser damage threshold, and solves the problem of the film firmly under low temperature deposition.
Locking laser frequency to an available reference standard can efficiently suppress the fluctuation of laser frequency and improve the frequency stability. In this paper, the Saturated Absorption Spectroscopy(SAS) and the Polarization Spectroscopy(PS) of rubidium D2 line were used to obtain the frequency discrimination curves. Then the error correcting signals from the frequency discrimination were sent in negatively feedback to the piezeo-electric transducer of a 780 nm external-cavity diode laser(ECDL) by electronic servo-system to realize the laser frequency locking. The basical principles and experimental schemes of two methods were introduced and the experimental results were compared. It shows that the residual fluctuations of laser frequency after being locked by using the two schemes are approximately 1.5 MHz and 0.6 MHz, respectively, compared with that of about 6.6 MHz for the case of ECDL free running. Furthermore, the PS scheme shows better frequency stability than SAS scheme, for SAS brings extra frequency noise by use of the phase sensitive detection which needs to modulate the laser frequency, while PS scheme is completely modulation-free.
Pulsed non-chain deuterium fluoride(DF) lasers based on the chemical reaction are proper sources of powerful coherent radiation in the 3.5-4.1 m spectral regions and they have intrinsic ability to store high levels of energy. These advantages make DF laser attractive to researchers in the mid-infrared laser field. In order to effectively improve the output performance of non-chain DF lasers, the key technologies of DF lasers were researched in this paper. The key technologies including self-initiated volume discharge, mixture ratio and recirculating and cooling were introduced. Particular emphasis was put on self-initiated volume discharge. These technologies will provide theoretical guidances for the further research on DF lasers.