2012 Vol. 5, No. 3
Single-phase white-light emitting phosphors BaMg2Al6Si9O30∶ Eu2+,Tb3+,Mn2+ are synthesized by solid state reaction. The energy transfers from Eu2+ to Tb3+ and Eu2+ to Mn2+ in BaMg2Al6Si9O30 are demonstrated by fluorescent spectra, energy transfer efficiency and fluorescent life time analysis. The BaMg2Al6Si9O30∶ Eu2+,Tb3+,Mn2+ shows three emitting colors: 450, 542 and 610 nm, which are assigned to the contribution from Eu2+, Tb3+ and Mn2+, respectively. By tuning the relative composition of Tb3+/Mn2+, chromaticity coordinates of (0.31, 0.30), color rendering index Ra=90 and Correlated Color Temperature(CCT) of 5 374 K can be achieved upon the excitation of UV light. Experimental results indicate that the present phosphor BaMg2Al6Si9O30∶ Eu2+,Tb3+,Mn2+ can serve as potential candidates for light emitting diodes.
Integral imaging technology is a three-dimensional display technology of picking up and displaying stereo images by using a lens array. For its wider applications, this paper overviews the characteristics of integral imaging three dimensional display systems. As the performance of integral imaging three-dimensional display system is limited by the resolution, depth and the viewing angle, the research progresses of enhancing the resolution, depth and the viewing angle in recent years are comprehensively discussed and the relative merits of various methods are compared and analyzed. At the same time, it gives the research present situation of the integral imaging three-dimensional display technology and describes the work by the author's research group in this field.
As for the lightweight structure of a large-aperture primary mirror in remote sensors, this paper introduces an optimized multi-target Genetic Algorithm(GA) based on the Kriging approximate model to design all lightweight structure paramaters for a 2 m-aperture SiC primary mirror. The latin hypercube method is used to build the Kriging model and do the experimental design of optimized parameters, and then a optimal solution is obtained through the multi-target GA(NSGA II). After the optimization, the 2 m-aperture SiC primary mirror weights 243 kg, the surface accuracy reaches 25.7 nm PV, 4.7 nm RMS and the total lightweight rate is 84%. The experimental result proves the feasibility of this optimization method and it can be a reference for the future lightweight optimization design of the structural parameters of large-aperture primiary mirrors.
A design based on 1.2 m lightweight SiC primary mirror is presented. An 18 point Whiffle-tree structure and a pressure bar are used for the axial support, and an A-Frame flexure mechanism and a tangent link are used for the lateral supporting system. The project of primary mirror design is disscussed in the principle, and the advantages are given. The parameters of mechanism are analyzed and optimized by the Finite Element Analysis(FEA) method. The whole FEA model is established, and the statics and thermal simulation analysis are accomplished. Experiments indicate that the Root Mean Square(RMS) of the mirror resulted from the supporting system is 3.5 nm at reference temperature, and it is 11.1 nm when the temperature difference is 40 ℃. The results show that the design could suit for the 1.2 m lightweight SiC mirror well, and thermal effect could be compensated successfully.
In order to achieve the high accuracy temperature measurement for a uncooled long-wave infrared thermal imager under different ambient temperatures, the radiometric calibration model of the infrared thermal imager is established in consideration of the effect of detector operation temperature. The radiometric calibration experiment is then conducted, and sixteen functional relations between image gray levels and detector operation temperatures at different blackbody temperatures and different brightness gain values are obtained. The mathematical calculation model of target temperature is established and the calibration result is verified by experiments. The results show that the detector operation temperature effect can be treated linearly in the range from 25 ℃ to 40 ℃, and it is independent on the target temperature. By setting an appropriate brightness gain, the temperature measurement error of the infrared thermal imager is less than 0.5 ℃, which is a great improvement of the measurement accuracy of the uncooled long-wave infrared thermal imager under different ambient temperatures.
In order to realize tracking and measurement for targets, a laser radar system based on image tracking is designed. The system produces a three dimension image with distance and angle information by a two dimension mechanically scanning of laser beam. It uses the miss distance, difference of azimuth and the pitch between the center of moving target and the field of view of scanning to drive the servo mechanism to keep the target in the center of sight to track the target in real time. At the same time, the valuable information of distance and angle is exported. Through a series of experiments on the system, it shows that for the target at the distance of 900 m, the accuracies of distance measuring and angle tracking are better than 0.25 m and 0.07?, respectively, and the ability of tracking is better than 1.2(?)/s. The system achieves the system miniaturization, fast acquisition targets, high accuracy measurement and tracking.
In order to obtain better de-noising effects and higher Signal-to-noise Ratios(SNRs) for recognizing small targets, the local variance estimation method is adopted to calculate the threshold. Different thresholds are selected for all the high-frequency sub-bands in wavelet decomposition levels. The improved hyperbolic function is used as the threshold function for wavelet coefficients more than the thresholds and exponential and logarithmic functions are combined as the threshold function for wavelet coefficients less than the thresholds. The adopted threshold function is derived theoretically and compared experimentally with those of soft and hard threshold methods. Computer simulation results show that the SNR is improved by 70.8% with the threshold method adopted in this paper, while they are improved by 49.8% and 59.7% respectively by using soft and hard threshold methods. By optical experiments, it is further proved that the method can improve SNRs and enhance the recognition ability of small targets with Joint Transform Correlator(JTC) more effectively.
An infrared target recognition method based on the invariance of spectral angle in time sequence is proposed to recognize spatial targets and balloon decoys. The difference between spatial targets and balloon decoys on the time-varying characteristics of temperature is gained. In order to reflect the time-varying characteristic essence of target measurement power temperature and to eliminate the time-varying coupling influence of the sensor, target distance and the equivalent projective area on the power measurement, the sequential spectral angle is presented as a sequence varying measure of the spectral vector. The measure can depict the sequence varying of the spectral curve and unti-demonstrate the time-varying characteristics of object temperature by the measurement, and it is regarded as an efficiency criterion of clustering recognition concept between targets and decoys. Simulation result shows that this method could effectively recognize spatial targets and balloon decoys. It provides a new mechanism for space target recognition by merging the sequential spectral characteristics.
To test an aspheric surface with an interference way in high-precision, a new method for determining the optimum positions of incident spherical wave source and reference spherical wave source are proposed. The optimal position of incident spherical wave source is determined by calculating the interferometric fringe density between incident spherical wave and aspherical reflective wave and that of the reference spherical wave source is obtained from calculating the interferometric fringe density on a CCD. On the theoretical basis of this research, the specific strategies of selecting CCDs and optical components can be determined and the interferogram can be fully analyzed to get much information about tested aspheric surfaces. It is shown that the research results can be used for theoretically guiding the debugging process of testing aspheric surfaces.
As for the operating requirements of spectrometer detector windows operating from visible to the infrared spectrum, the TiO2, M1 and SiO2 were chosen as coating materials with different refractive indexes and were designed into film stacks by various schemes. By using electron beam evaporation with ion beam assist deposition, the visible/near infrared ultra-broad band antireflective coatings with excellent optical properties, good repetition and firmness were prepared by parameter adjustment. The average transmittances of these coatings are better than 99% at (650?10) nm, 900-1 100 nm and (1 470?10) nm, and better than 97% in 620-1 550 nm as a whole. It meets the actual requirements of the spectrometer detector windows well.
The applications of spectral technologies in intense laser damage are introduced by taking the temperature retrievals of thermal radiation spectra for example. A self-made high speed spectrum measurement system is used to collect radiation spectra for intense laser damage in real-time. The damage zone temperature is obtained through the temperature retrieval based on the principle of Planck's black body radiation, and the temperature distribution of a damage zone is calculated by using the principal component regression. The measurements of transient temperature and temperature distribution for intense laser irradiating targets are realized, and the spectral range is 200-1 000 nm corresponding to the temperature retrieval range for 700-6 000 ℃.
A compact CO2 laser with short pulse duration, high peak power and high repetition was developed by using an Acousto-optic(AO) Q-switch. The operating principle of the AO Q-switch was analyzed, and the theoretical model of CO2 laser was introduced based on the small-signal gain and saturation intensity. Then the optimal numerical solution of the transmission for an output mirror was given by this model. Based on the compact CO2 laser in our laboratory, the experiments to verify the theoretical result were performed. The optimal coupling output factor gained by the theory and experiments is 39%. The variable law of laser output performance with pulse repetition frequency was researched. Results show that the peak power of the laser will fall down when the pulse repetition frequency is greater than 1 kHz, which is related to the radiation life of CO2 molecular upper energy level, and is limited by the heat effect of AO Q-switch. The range of pulse repetition frequency can be adjusted from 1 Hz to 100 kHz. When the pulse repetition frequency is 1 kHz, the measured pulse duration is 156 ns and the peak power is 10 kW. The laser has good stabilization, and is suitable for a light source used in laser-matter interaction.
To investigate the influence of turbulence on the laser propagation through atmosphere, the simulation technology of the turbulence was analyzed. The numerical simulation technology for the turbulence on laser propagation in laboratory was introduced and turbulence simulation systems were also discussed. A detailed description and the comparison for Fast Fourier Transform(FFT) and Zernike polynomial methods of numerical simulation were offered and a turbulence simulation system was established by a static phase screen. The theoretical model and the simulation experiment were also performed, then energy intensity distribution of laser propagating in the tarbulence simulation system were studied. The results show that the system can simulate the weak fluctuation turbulence accuretely.
A liquid crystal grating(LCG) with viriable grating constants is designed to make up for the shortcomings of existing gratings, such as fixed grating constant, electrode tip discharge and the electrode edge effect, et al. As a bias is applied to different conducting regions by a control module, the local transmittance is variable and location dependent, which may achieve the transition of grating constant. In addition, the arc-shape design for honeycomb electrode can efficiently avoid the point discharge near the tip and can reduce right-angle shape effect on the deflection texture. The LCG is tested by a WGD-8A grating multi-function analyzer with a He-Ne laser as the light source. The experimental results indicate that the grating constant can be changed by the control module. With the driving voltages of 2-3.4 V, the first order diffractive intensities and their difference values of the liquid crystal grating with three different grating constants increase gradually. This type of LCG can be wildly applied in many devices, such as parallax barriers and grating rulers, which are significant for the application and development of LCGs.
A Microchannel Plate(MCP) photon detector was developed to detect the 30.4 nm radiation in a plasma layer of the earth. By changing voltages, temperatures and other parameters, the variations of the dark noise and resolution for the MCP detector were compared. The results indicate that the dark noise of the detector comes from the ion feedback of residual gas and the thermal noises mainly. Therefore, to reduce the dark noise, the microchannel should be preprocessed by removing residual gases and the detector could not work at a high temperature state. After preprocessing at the room temperature, the dark noise counting rate of the detector has reduced to 0.34 count/s穋m2. Furthermore, the temperature has a little effect on the resolution of the detector, and the resolution dependents on the variances of voltage or counting rate obviously. With different resist pressure abilities for different MCPs, it demonstrates that the proper voltage or counting rate can provide a better resolution.