Cr4+:YAG飞秒脉冲激光器光路结构的优化设计

通过理论分析和数值计算,对Cr4+:YAG飞秒脉冲激光器光路结构的优化设计进行了研究.提出了在谐振腔内插入一薄聚焦透镜代替另一折叠镜以降低光路的复杂性.为研究起色散补偿作用的棱镜对对腔的稳定性和像散带来的影响,导出了棱镜对的光传输矩阵.通过编程计算得出了连续运转和锁模运转两种工作方式下的不同参数的谐振腔稳区图,对激光器工作点的选择做出了论述.定义了像散补偿失配因子F,做出了像散补偿区域分布图.指出F<0.05的区域具有良好的像散补偿特性,也是激光器光路结构参数设计必须要考虑的重要方面.论证了改变抽运光聚焦透镜的位置可实现抽运光与腔内振荡光的匹配.     

全固态窄线宽钠导星激光器

研制了一台重复频率400 Hz,平均功率1.0 W的激光二极管抽运全固态窄线宽钠导星激光器.利用两路波长分别为1064 nm和1319 nm的声光(AO)调Q激光器作为基频光,在腔外通过三硼酸锂(LBO)晶体和频产生(SFG)589 nm钠导旱激光,和频效率约达20%.每路基频光均采用标准具压窄线宽,输出和频光线宽约1.8 GHz,并调节控制标准具的温度和倾斜角度将中心波长锁定于589.159 nm(偏差±1 pm),实现了激光器谱线与钠原子D2线的精确匹配.     

Mutual injection-locking of two individual double-clad fibre lasers

Phase-locking and coherent beam combination of two individual double-clad fibre lasers by a novel extra-cavity mutual injection-locking method are proposed and experimentally demonstrated. Steady interference stripes with high contrast ratio (about 0.5) are observed. The output power of the phase-locked array exceeds 11 W and the power-combining efficiency is about 80%. No power-restriction optical components are utilised in the phase-locking experiment and the output power can be further up-scaled.     

打击治理伪基站的问题及建议

本文分析了当前伪基站发展的新动向以及打击治理伪基站面临的新难题,在此基础上提出相应的对策建议.     

三网融合下广电媒体网内整合模式创新探讨

广电行业2010年进入改革阶段,目前进入深化改革阶段,此番改革是前所未有的,是三网融合背景下行业发展的必然趋势。立足广电媒体工作实践,从三网融合背景出发,探究广电媒体网内整合的创新模式,以期能够促进广电媒体发展,加快网内整合步伐。     

传感器网络多址接入协议的实现

无线传感器网络(WSN)由于其巨大的应用潜力成为近年来研究者们广泛关注的热点问题.WSN中的多址接入协议(MAC-Medium Access Control)决定了各节点是否能够高效的共享信道,因此直接影响到了WSN的性能.文中针对突发业务环境的无线传感器网络实现了一种新型S_MAC协议,详细论述该协议设计中的关键步骤以及对应的策略,并将该算法移植到了传感器节点的开发平台上.最后通过在硬件平台的测试,得到了正确的输出波形.     

Studies on Fast Algorithm for the Scattering of a Large Array of Waveguide-Fed Wide-Slot Antennas in Millimeter Wave Region

We present an effective numerical technique to characterize the scattering of wide-slot antennas fed by waveguides with arbitrary terminations in terms of the method of moment (MoM) and the mixed potential integral equation (MPIE). In particular, the precorrected-fast Fourier transform (P-FFT) eliminates the need to generate and store the usual square impedance matrix andthus leads to speed up the matrix-vector multiplication in the resultant system. This property makes the Rao-Wilton-Glisson (RWG) functions to be useful in simulating electrically large-scale problems. In addition, the scattering from the finite ground surfaces is accounted for in the total scattered field by using the method of equivalent edge currents. The numerical results are presented and compared with both the traditional method of moment results obtained using the entire-domain basis functions and the experimental results, to demonstrate the proposed method to be a good candidate for study on the scattering of arbitrary wide-slot large array.     

Room-temperature electroluminescence of p-ZnxMg（1-x）O：Na/n-ZnO p-n junction light emitting diode

p-ZnxMg1-xO：Na/n-ZnO p-n junction light emitting diode （LED） was produced on n-ZnO （0001） single-crystal substrate using pulsed laser deposition. The realization of band gap engineering was achieved by the incor-poration of Mg in ZnO layers and was confirmed by photoluminescence spectrum. The p-type ZnxMg1-xO：Na film with low resistance was obtained at 500 ℃ and in which, Na has taken effect evidenced by Hall and X-ray photo-electron spectroscopy measurements. The current-voltage curve of LED showed a rectifying behavior and obvious electroluminescence was realized by feeding a direct current up to 40 mA. Furthermore, its structural and electric characters are discussed as well.     

Speech Enhancement Algorithm Based on MMSE Short Time Spectral Amplitude in Whispered Speech

An improved method based on minimum mean square error-short time spectral amplitude （MMSE-STSA） is proposed to cancel background noise in whispered speech. Using the acoustic character of whispered speech, the algorithm can track the change of non-stationary background noise effectively. Compared with original MMSE-STSA algorithm and method in selectable mode Vo-coder （SMV）, the improved algorithm can further suppress the residual noise for low signal-to-noise radio （SNR） and avoid the excessive suppression. Simulations show that under the non-stationary noisy environment, the proposed algorithm can not only get a better performance in enhancement, but also reduce the speech distortion.     

A NEW DEFORMABLE MODEL USING LEVEL SETS FOR SHAPE SEGMENTALTION

In this paper,we present a new deformable model for shape segmentation,which makes two modifications to the original level set implementation of deformable models.The modifications are motivated by difficulties that we have encountered in applying deformable models to segmentation of medical images.The level set algorithm has some advantages over the classical snake deformable models.However,it could develop large gaps in the boundary and holes within the objects.Such boundary gaps and holes of objects can cause inaccurate segmentation that requires manual correction.The proposed method in this paper possesses an inherent property to detect gaps and holes within the object with a single initial contour and also does not require specific initialization.The first modification is to replace the edge detector by some area constraint,and the second modification utilizes weighted length constraint to regularize the curve under evolution.The proposed method has been applied to both synthetic and real images with promising results.