Polarization controlled multiwavelength switchable erbium-doped fiber laser based on high birefringence few-mode fiber loop mirror

A multiwavelength switchable erbium-doped fiber laser with linear cavity is proposed and experimentally demonstrated. It is based on a fiber loop mirror incorporating a piece of high birefringence few-mode fiber and polarization controller. Due to dependence of its reflection properties on the polarization controllers, the fiber laser can operate in the random combination of three wavelengths by only adjusting the polarization controllers in the linear cavity. The wavelengths involved in the switching operation are determined by the merged Sagnac and intermodal interferences elicited in the fiber loop mirror. The optical signal to noise extinction ratio of every oscillation line is higher than 40 dB and power fluctuation less than 0.5 dB.     

W波段TE62-TEM00准光模式变换器

对准光模式变换器的基本理论和设计方法进行了讨论.以改进型等效电流理论为基础给出了Vlasov辐射器的分析方法,建立了数值模型,并进行了计算分析.继而推导了自适应相位修正Katsenelenbaum-Semenov算法,编制了相位修正反射镜自适应设计分析程序.在上述理论工作的基础上,针对3 mm波段TE62至TEM00准...     

激光烧蚀脉冲放电激发的土壤等离子体电子数密度和温度的研究

以激光烧蚀快脉冲放电激发土壤为例,研究了激光烧蚀快脉冲放电等离子体技术产生的土壤等离子体的电子数密度和温度。根据实验测得的Si原子和离子谱线的强度和萨哈玻尔兹曼方程,计算了等离子体的电子温度,并从分析Si I 250.69nm谱线的斯塔克展宽中导出了等离子体的电子数密度。与使用同样激光能量激发的激光等离子体相比,激光烧蚀快脉冲放电激发等离子体的电子数密度和温度都明显增加,与观察到的光谱信号强度是一致的。     

Low-frequency and broad band metamaterial absorber: design, fabrication, and characterization

We report a metamaterial absorber (MA) with a broad absorption band in the frequency region of 2–4 GHz, whose thickness is not limited to the quarter-wavelength. Theoretical and experimental results show that the absorber has two adjacent absorption apexes at 2.24 and 3.46 GHz, respectively, which are both related to the electric and magnetic resonances of the metamaterial. The absorption is over 68% in the whole wave band of 2–4 GHz provided the thickness of 4 mm. The distributions of the surface currents and the power loss density indicate that the surface currents produced by the electric and magnetic resonances are strongly consumed by the resistive patches. This low-frequency absorber has potential applications in many scientific and martial fields.     

基于光子筛的软X光谱仪

 介绍了采用新型软X光谱学光子筛作为分光元件的软X光谱仪的原理和结构参数设计。新谱仪理论测量范围为100 eV~2 keV,光谱分辨力达0.35 nm。应用该谱仪在SILEX-Ⅰ装置上测量了飞秒激光与固体铜靶相互作用产生的X射线发射谱。实验结果表明,该谱仪主要性能指标达到设计要求,适合于激光与等离子体相互作用产生的软X射线研究。     

Numerical analysis of the output power of the injection-locked cw Ti:sapphire lasers

The optimization analysis of the output power of the injection-locked cw Ti:sapphire lasers is presented based on the fact that the injection-locked and free-running lasers almost have the same maximum output power. With the modified Ti:sapphire laser model, the dependences of the threshold and slope efficiency on the ring cavity and crystal parameters are studied through the numerical calculations, which clarify the roles of various parameters in affecting the output power. Our calculated results are in good agreement with the reported experimental data for the laser at 756 nm. Therefore our numerically calculated results could be used as a guideline for designing and optimizing such kind of the lasers.     

基于Demons算法改进的图像去噪模型研究

在Demons算法的基础上, 将扩散过程看作图像配准, 建立一种新的基于图像配准的Demons 去噪模型. 实验表明, 该模型去噪效果优于经典的Perona-Malik模型, 排除了模型的病态性. 考虑到新模型在图像去噪过程中仅靠梯度信息表示图像的局部特征还不完善, 故将水平集曲率作为控制图像结构的驱动力因素引入到此模型中, 提出了一种新的梯度和曲率双重驱动力的图像去噪模型. 分析和仿真结果表明, 两种新模型都可有效抑制噪声, 清晰度也有明显的提高, 其中双重驱动力的图像去噪模型去噪效果更具优越性.     

Wide-band circular polarization-keeping reflection mediated by metasurface

In this paper,we show that circular polarization-keeping reflection can be achieved using reflective metasurfaces.The underlying physical mechanism of the polarization-keeping reflection is analyzed using a reflection matrix.A wideband circular polarization-keeping reflector is demonstrated using N-shaped resonators.Both the simulation and experiment results show that the polarization-keeping reflection can be achieved with a high efficiency larger than 98%over the frequency range from 9.2 GHz to 17.7 GHz for both incident left-and right-handed circularly polarized waves.Under oblique incidence,the bandwidth increases as the incident angle varies from 0°to 80°. Moreover,the co-polarization reflection is independent of the incident azimuth angles.     

Frequency-locking and threshold current-lowering effects of a quantum cascade laser and an application in gas detection field

In this paper,the frequency-locking and threshold current-lowering effects of a quantum cascade laser are studied and achieved.Combined with cavity-enhanced absorption spectroscopy,the noninvasive detection of H_2 with a prepared concentration of 500 ppm in multiple dissolved gases is performed and evaluated.The high frequency selectivity of 0.0051 cm~(-1) at an acquisition time of 1 s allows the sensitive detection of the(1-0) S(l) band of H_2 with a high accuracy of(96.53±0.29)%and shows that the detection limit to an absorption line of 4712.9046 cm~(-1) is approximately(17.26±0.63) ppm at an atmospheric pressure and a temperature of 20 ℃.     

低密度稀土氧化物基气凝胶靶的研制

低密度的高原子序数元素氧化物气凝胶由于前驱体形成端基双键而易于收缩和开裂。通过调控配位环境结合无机分散溶胶凝胶法,制备了稀土氧化物气凝胶。氧化镧基气凝胶和氧化钇基气凝胶块体的成型性好,最低密度分别为0.05g·cm-3和0.06g·cm-3。其成分分别为六方相的La(OH)3和六方相的Y(OH)3,而聚丙烯酸中的羧基与稀土离子之间以桥接的方式进行配位。两种气凝胶均存在明显的多级结构,氧化镧基和氧化钇基气凝胶的初级粒子分别为纤维状和片/球混合形貌,而其二级粒子均为球形。两种气凝胶的比表面积分别为229.1m2·g-1和229.6m2·g-1。该方法制备的稀土氧化物气凝胶具有低的密度和纳米尺度的均匀性,在背光源中有潜在的应用。