Wideband supercontinuum generation in tapered tellurite microstructured fibers

Enhanced soliton trapping of dispersive waves in a tapered tellurite microstructured fiber pumped by a 1556 nm femtosecond fiber laser is demonstrated. The short wavelength edge of supercontinuum light is extended from 960 to 600 nm after tapering the tellurite microstructured fiber, which is caused by the enhanced soliton trapping of dispersive waves owing to the changing group velocities in tapered fibers. Wide-band supercontinuum light source spanning from 600 to >2400 nm is generated in tapered tellurite micro-structured fibers. Our experimental and simulated results show that short length (several centimeters) zero-dispersion-wave length decreasing highly nonlinear fiber has a potential for generating wideband supercontinuum light source expanding from visible to mid-infrared region.     

异地时钟同步与时间的度量

介绍了庞加莱等人关于"异地时钟同步"和"相继时间段(绵延)相等"的思考,介绍了爱因斯坦"约定"异地时钟"同时"的方案,以及朗道等人对该方案的发展.我们赞同庞加莱的设想,即对光速传播性质的约定是时间测量的基础,并指出对光速的约定相当于对时空对称性的约定.我们在"约定光速的基础上"给出了钟速同步具有传递性的条件,不仅解决了"异地坐标钟钟速同步"的定义问题,而且解决了"相继时间段相等"的定义问题,证实了庞加莱原初的猜想,简化了时间测量的理论基础.     

一种新型径向三腔同轴虚阴极振荡器全三维粒子模拟研究

提出了一种新型径向三腔同轴虚阴极振荡器,并进行了数值模拟研究. 研究表明: 这种径向三腔结构在束波转换面进行电场调制,能够大幅提高束波转换效率;同时,由阳极栅网和径向三腔结构构成的谐振装置能有效地抑制模式竞争;另外,由于采用了同轴引出结构,在提高能量引出的同时还能有效吸收漂移管中被利用过的电子,因此这种新型虚阴极振荡器能够获得较高的输出功率. 模拟的电子束电压为400 kV,电流为50 kA,主频为4.5 GHz,峰值功率达到6 GW,平均输出功率为3.1 GW,束波转换效率达到15%. 关键词： 高功率微波 同轴虚阴极振荡器 粒子模拟 束波转换效率     

基于波数均匀展宽模型的全反射傅里叶变换成像光谱仪高精度光谱定标处理方法

全反射傅里叶变换成像光谱仪ARFTIS(all-reflection Fourier transform imaging spectrometer)是基于FT成像光谱理论的一种新型仪器,它不但具有高光谱分辨率特点,而且还具有宽波段、无色差的特点,特别适合应用在宽波段成像的遥感领域.目前常用的光谱定标方法有单色法、平均法...     

Single atom entropy squeezing for two two-level atoms interacting with a binomial field

In this paper we consider a system of two two-level atoms interacting with a binomial field in an ideal cavity. We investigate the time evolution of the single atom entropy squeezing, atomic inversion and the linear entropy for the present system. Furthermore, the relationship between the entropy squeezing and the entanglement is investigated. It is shown that the amounts of the nonclassical effects exhibited in the entropy squeezing are dependent on the different initial conditions. The entropy squeezing can give information on the corresponding linear entropy.     

Room-temperature anomalous Hall effect and magnetroresistance in (Ga, Co)-codoped ZnO diluted magnetic semiconductor films

This paper reports that the(Ga,Co)-codoped ZnO thin films have been grown by inductively coupled plasma enhanced physical vapour deposition.Room-temperature ferromagnetism is observed for the as-grown thin films.The x-ray absorption fine structure characterization reveals that Co 2+ and Ga 3+ ions substitute for Zn 2+ ions in the ZnO lattice and exclude the possibility of extrinsic ferromagnetism origin.The ferromagnetic(Ga,Co)-codoped ZnO thin films exhibit carrier concentration dependent anomalous Hall effect and positive magnetoresistance at room temperature.The mechanism of anomalous Hall effect and magneto-transport in ferromagnetic ZnO-based diluted magnetic semiconductors is discussed.     

多壁碳纳米管膜湿敏特性的研究

研究了多壁碳纳米管(MWNTs)薄膜的湿敏特性，实验所用的多壁碳纳米管是用热灯丝化学气相沉积法(CVD)合成的.分别对未修饰和修饰的多壁碳纳米管膜温度和湿度特性进行研究后发现，修饰的多壁碳纳米管对温度和湿度非常敏感，且对湿度的响应时间和恢复时间短，重复性好.而未修饰的多壁碳纳米管对温度和湿度不太敏感.对修饰多壁碳纳米管的湿敏特性进行了理论分析，给出了其理论表示式. 关键词： 多壁碳纳米管 化学修饰 湿敏特性 物理吸附     

RuH2和RuN2电子组态与光谱性质的从头计算

用量子化学从头算方法在B3LYP/6 311G 的水平上 ,研究了RuH2 和RuN2 可能的电子组态和光谱性质 .结果表明 ,RuH2 的3 B2 和5Σ-态对应于静电作用的物理吸附态 .RuN2 的一重态和三重态的计算结果跟钌单晶面上的实验值相接近 .而RuN2 在C∞v对称性时 ,五重态5Σ-的计算频率比实验值稍低 .在C2v对称性时 ,五重态的计算频率值则更低 ,3 B2 和5A1态不能稳定存在     

Optoacoustic imaging with synthetic aperture focusing and coherence weighting

Optoacoustic imaging takes advantage of high optical contrast and low acoustic scattering and has found several biomedical applications. In the common backward mode a laser beam illuminates the image object, and an acoustic transducer located on the same side as the laser beam detects the optoacoustic signal produced by thermoelastic effects. A cross-sectional image is formed by laterally scanning the laser beam and the transducer. Although the laser beam width is generally narrow to provide good lateral resolution, strong optical scattering in tissue broadens the optical illumination pattern and thus degrades the lateral resolution. To solve this problem, a combination of the synthetic aperture focusing technique with coherence weighting is proposed. This method synthesizes a large aperture by summing properly delayed signals received at different positions. The focusing quality is further improved by using the signal coherence as an image quality index. A phantom comprising hair threads in a 1% milk solution was imaged with an optoacoustic imaging system. The results show that the proposed technique improved lateral resolution by 400-800% and the signal-to-noise ratio by 7-23 dB over conventional techniques.     

Proton-exchanged optical waveguides fabricated by glutaric acid

In this paper, we first report that a new proton source, glutaric acid, has been used to fabricate optical waveguides in Z-cut lithium niobate crystals. The relationship was experimentally established between proton-exchanged (PE) waveguide parameters and fabrication conditions. It is shown that this new organic acid can be used to obtain deep PE waveguides in fast diffusion speed (0.275 μm²/h at 221°C) and with low loss (0.2 dB/cm). It provides an alternative approach for fabricating PE waveguides in lithium niobate substrate.