2009 Vol. 2, No. 3
On the basis of the theory of interferometric imaging, this paper introduces the theory of optical synthetic aperture imaging technique. Then, two types of synthetic aperture imaging systems, Michelson interferometry and Fizeau interferometry, are compared in imaging processes, imaging characteristics, sizes of visual field and the scopes of application, and the present situation and developing trends of both Michelson and Fizeau synthetic aperture telescopic systems for ground based and spacebased are described. It points out that the development of the former will focus on the long and complex base line structures and the latter will emphasize the complex apeature arragement to form a equivalent aperture that is several times or tens times that of original one. Compared to traditional optical systems, the optical synthetic aperture system is characterized by its high resolving powers， small mass and costs and easy to be folded, so it is a useful approach to higher resolving powers. Finally, it is proposed that several kinds of new techniques such as lucky imaging, launching by module and assembly in an orbit, unsupported membranes can be also introduced into the synthetic aperture imaging technique.
Traditional space telescopes can improve the resolution by increasing the system aperture in accordance with the diffraction limit formula of resolution. However, as the corresponding volume and weight of the system are increased, it is difficult to be carried on a spacecraft. The emergence of Negative Index Materials(NIMs) provides a new way for the development of highresolution space telescopes. This paper introduces the history and research of NIMs and outlines their special properties, such as negative group velocity, inverse Doppler effect, abnormal Cerenkov radiation and negative refraction effect, then it discusses the functions of NIMs and why the NIMs can be used to improve the telescope resolution. It points out that NIMs amplify evanescent fields containing information of the fine structure of objects and decaying exponentially in a vacuum with distance, so that the evanescent fields can participate in imaging. These properties of the NIMs make the resolution of an optical system better than the traditional diffraction limit.
Atmospheric scintillation of uplink optical beam has the effect on reliability of the satellite-ground laser link. Based on time-averaging effects for atmospheric scintillation, extending photoelectric detector’s exposure time is one of the effective ways to mitigate the extent of atmospheric scintillation. Time-averaging effects of exposure time taken into account, expressions are derived for time-averaging factors for large zenith angles and small zenith angles, respectively. Based on the above, that the zenith angle and height above ground of an optical transmitter have the effect on the time-averaging is analysed. Results show that extending the exposure time mitigate the extent of the atmospheric scintillation of uplink optical beam. Along with the increase of the zenith angle and height above ground of an optical transmitter, the extent of the time-averaging effect decreases.
opto-electronic detection; complex warning; parameter modeling; Signal-to Noise Radio (SNR)
To evaluate performance of flashing light, a new system is made for intensity detection of flashing lights in this paper, which uses labview platform. Not only the flashing waveform in a certain period of time can be observed, but also can exactly calculate peak intensity, efficient intensity，flashing frequency and flashing time in a high-speed. We introduced the parameter calculate principle, hardware configuration and labview program design, a effectual method was proposed to resolve the problem of data losed easily in data acquisition process，and data can be store. The operation easily and any flashing waveform can be detected which flshing time greater then 0.1s, the acquisition maximum time can reach 10s. A batter evaluation of flashing light performance can be made by this system.
To measure the sub-pixel image motion which is caused by satellite attitude instability or vibration，the joint transform correlator method is designed. The mathematics principles were clarified, the position of matrix CCD on the focal plane and the method of getting input image were presented. Sub-pixel image motion input image which to be tested was got by linear interpolation and pixel combination. The results show that the error does not change with different scene of input images, and the error RMS of 0.2 has been achieved.
To prepare highly efficient optical sensors to UVA light, the following strategies were adopted. An organic photovoltaic (PV) device, in which 4,4′,4′′-tris[3-methylphenyl (phenyl)amino]triphenylamine (m-MTDATA) and Re(CO)3Cl-dipyrido [3,2-a:2',3'-c]phenazine (Re-DPPz) were used as electron donor and acceptor, respectively, has been fabricated. Under illumination with UV light (365 nm, 1.6 mW/cm2), the short circuit current (Isc), open circuit voltage (Voc), fill factor (FF) and power conversion efficiency of the PV device were measured to be 57.1μA/cm2, 0.86 V, 0.39, 1.2% respectively. These results indicate that the Re-DPPz complex, a promising triplet emitter in electroluminescence (EL) devices, also possesses good PV performance.
There is great influence on the output electro-optical convention efficiency for the different gas pressure and different gas mixture ratio in high power pulsed TEA CO2 laser. Therefore the output energy of laser changes with various gas pressures or various gas ratios in the laser resonator, which the convention efficiency of laser also increases accordingly. The experimental results show that the best value exists for laser output electro-optical convention efficiency when the gas ratio of CO2:N2:He equals 3:9:28. Under the condition of same injection exciting electric energy and total gas pressure 40kPa, the output energy can achieve 24.6J when single pulse discharges; the laser electro-optical convention efficiency can achieve 16.4% when laser works at high repetition rate and continuous discharge. Laser can operate continuously and steadily at maximum 500Hz.
The strong electromagnetic interference generated in the operation of the high-power TEA CO2 laser system mainly comes from the main discharge loop, pulse spark switch and power supply module. Such a strong electromagnetic interference has high interference and damage to the electronic systems inside and outside the laser system itself. The EMC of the laser system is designed based on the analysis and calculation of the electromagnetic interference to the laser system itself. The EMC problem of the high power TEA CO2 laser is settled by suppressing the propagation of the interference electromagnetic wave using two methods: one is the hardware method, the other is the software one. The hardware design way adopts electromagnetic shielding of the interference source and controlling sub-system, appropriate system layout and wiring, filtering isolation, while the software design way uses noise depression including data redundancy debugging, redundancy operation and data identification. The experimental results show that the adopted methods are effective and main ways in suppressing the interference and protecting the laser control sub-system to be damaged. Software anti-jamming is the extension and supplement of the hardware interference suppression methods, all the methods can guarantee the high reliability of the laser system.
In order to investigate high-power TEA CO2 laser, a high-power rotating spark switch is chose as a device of power switch. Therefore a pulsed exciting power supply is developed including a high voltage resonant charging circuit, a high anti-jamming switching trigger, a rotating spark switch and a draw-out L-C reverse circuit. The measurement and the research are conducted in the high-power TEA CO2 laser. The experimental results demonstrate that this pulsed exciting power supply developed by our lab can totally satisfy the special requirement of the high-power TEA CO2 laser. The repetition rate can adjust arbitrarily at the range of 100~400 Hertz, the output working voltage is up to 40kV~50kV, the average power of power supply is larger than 220kW and the peak power of this device is as high as 1000MW.
A compact multifunctional CO2 laser is constructed. This laser can work as behaviors of single pulse, repetition frequency or continuous and also realize the coding of pulse frequency and wavelength tuning. The resonator of laser adopts the operate mode of grating as zero-level output and first-order oscillation, which achieve pulsed laser output time from hundreds nanosecond level to sub-millisecond level by using the technology of acousto-optically Q-switched and impulsive discharge. The directional output device of grating tuning is introduced based on optical angle reflector in this laser with theoretical calculation and discussion. This device consists of rotating platform, infrared grating and plane mirror, which realize the directional and positional output of different wavelength. The pulse repetition rate is continuously tuning from 1 Hz to 10kHz and the tuning range of output wavelength is from 9.2μm to 10.8μm. The maximal continuous output power is 8W, the minimal width of pulse is 180ns and the maximal peak power is 4062W. This laser has great applied value in the scientific field of laser interacting with material, especially in the investigation of the mechanism of damage for the effect of laser to material.
Comparing with traditional stable resonator high-power TEA CO2 laser, it is always the key point to improve the optical beam quality as the same time guarantee the power of laser. Based on the original stable resonator, three sets of telescopic positive-branch confocal resonators is designed using unstable resonator scheme, which give the whole design process and theoretical analysis. The corresponding comparison experimental study are conducted with single-pulse energy, divergence angle and pulse duration time. Experimental results indicate that using unstable resonator can largely improve the divergence angle as the same time to maintain the high single-pulse energy. The single-pulse energy 13.7J, the divergence angle 1mrad (stable resonator as 2.4mrad) and pulse duration time 50ns (stable resonator as 98ns) are obtained from the best unstable resonator. This work will make this kind of laser to be widely used in the field of laser manufacture.
The related design of electrode with large area uniform electric field and the experimental results are introduced in this paper. The distribution of electric field is uniform between two electrodes with boundless parallel slab, but the problem is the uniform design of electric field in the condition of limited size of electrode. Therefore the theoretical and engineering computations are crucial to solve this problem. According the practical condition of TEA CO2 laser, Chang theory is chose as the reference of design. The experimental results of electrode discharge after the design show that the uniform glow discharge in large area is realized between two main electrodes. with 55mm electrode width and flatness part 40mm section. The TEA CO2 laser is able to continuously work for 10minutes in the condition of high repetition rate 500Hz.