Electrical generation of pure spin current with oscillating spin-orbit interaction

We propose an electrical scheme for the generation of a pure spin current without a charge current in a two-terminal device, which consists of a scattering region of a two-dimensional electron gas (2DEG) with Rashba (R) and/or Dresselhaus (S) spin-orbit interaction (SOI) and two normal leads. The SOI is modulated by a time-dependent gate voltage to pump a spin current. Based on a tight-binding model and the Keldysh Green’s function technique, we obtain the analytical expression of the spin current. It is shown that a pure spin current can be pumped out, and its magnitude could be modulated by device parameters such as the oscillating frequency of the SOI, as well as the SOI strength. Moreover, the spin polarisation direction of the spin current could also be tuned by the strength ratio between RSOI and DSOI. Our proposal provides not only a fully electrical means to generate a pure spin current but also a way to control the spin polarisation direction of the generated spin current.     

Towards a monolithic optical cavity for atom detection and manipulation

We study a Fabry-Perot cavity formed from a ridge waveguide on a AlGaAs substrate. We experimentally determined the propagation losses in the waveguide at 780 nm, the wavelength of Rb atoms. We have also made a numerical and analytical estimate of the losses induced by the presence of the gap which would allow the interaction of cold atoms with the cavity field. We found that the intrinsic finesse of the gapped cavity can be on the order of F∼30, which, when one takes into account the losses due to mirror transmission, corresponds to a cooperativity parameter for our system C∼1.     

Correlations in photon-numbers and integrated intensities in parametric processes involving three optical fields

Two strongly-pumped parametric interactions are simultaneously realized in a single nonlinear crystal in order to generate three strongly correlated optical fields. By combining together the outputs of two of the three detectors measuring intensities of the generated fields, we obtain the joint photocount statistics between the single field and the sum of the other two. We apply a microscopic quantum theory developed earlier to determine the joint photon-number distribution and the joint quasi-distributions of integrated intensities and prove nonclassical nature of the three-mode state. Finally, by performing a conditional measurement on the single field, we obtain a state endowed with a sub-Poissonian statistics, as testified by the analysis of the conditional Fano factor. The role of quantum detection efficiencies in this conditional state-preparation method is discussed in detail.     

Entanglement generation in a two-mode single-atom laser

We present a method of generating two-mode single atom laser based on the nonresonant interaction of a three-level Λ type atom in a two-mode cavity with three strong classical driving fields. An analytical solution for this effective dynamics under the presence of the cavity losses is obtained, which allow us to analyze the entanglement properties and the photon statistics of the two cavity modes exactly. It is also shown that the possible generation of the two-mode entangled coherent states in the transient regime after the atomic measurement.     

长周期波导光栅窄带光滤波器特性的模拟

利用两路平行的刻有长周期光栅(LPWG)波导间耦合的理论模型,研究了LPWG波导光滤波器,利用弱耦合实现高耦合效率和窄带滤波的方法,设计了一个窄带光滤波器。仿真结果表明,在1 530~1 560 nm范围,能实现单一的带通、带阻互补滤波输出,3 dB带宽为1 nm,耦合效率高达98%。     

纳米光纤的色散特性及其超连续谱产生

通过数值计算,分析了纳米光纤的色散特性,并比较了纳米光纤中不同直径和不同材料的色散特性.结果表明：二氧化硅纳米光纤有两个零色散波长,随光纤直径的增大,其色散曲线趋于平坦,零色散波长也随之发生改变;硅光纤只有一个零色散波长,且随着直径的增大,零色散波长向长波方向移动.采用广义非线性薛定谔方程来描述超短激光脉冲在纳米光纤中的传输演化过程,利用分步傅里叶方法求解方程.比较了超短脉冲在光纤不同色散区传输时,色散对超连续谱产生的影响以及脉冲波形的演化.在正常色散区,超连续谱谱宽很窄,而在零色散区和反常色散区则可产生 关键词： 色散 超连续谱产生 非线性光学 纳米光纤     

基于布拉格反射镜的X射线多色单能成像谱仪

报道了一种基于布拉格反射镜的多色单能成像谱仪研制工作,谱仪由针孔阵列、布拉格反射镜和CCD相机组成.大约有300个微孔的针孔阵列板置于布拉格镜前用于空间成像,通过布拉格反射镜的单色化,投射到CCD上的数百个小孔成像沿色散方向获得了能量分辨.经过图像处理,可以还原得到目标的多色单能二维成像.根据采用的布拉格分光元件和图像还原方法,谱仪的能量分辨达到了50—200（λ/Δλ）;针孔成像的空间分辨优于10 μm.同时还为该谱仪开发了专门的单能图像重建软件及图像数据后处理软件,可以在任意选择的窄能带内还原准单能图像.并重点介绍了该谱仪的优化设计、获得的技术指标以及专门研制的超短周期（2.5 nm）X射线W/B₄C多层镜. 关键词： X射线光学 诊断技术 布拉格反射镜 X射线多层镜     

基于表面等离子体激元共振的飞秒抽运探测技术研究

对基于表面等离子体激元共振（SPR）的飞秒抽运探测技术进行了系统地数字分析.计算结果表明,利用SPR技术可将飞秒抽运探测信号强度ΔR/R提高2—3个数量级,其提高的比例依赖于金属膜的厚度和探测光的入射角,其中R和ΔR分别为探测光反射率的总量和变化量.特别地,对于金属-吸收介质体系,金属膜的介电常数变化对ΔR的影响仅为吸收介质影响的2%,所以ΔR/R主要反应吸收介质中的动力学过程,因此该技术对研究表面和界面的超 关键词： 超快光学 表面等离子体共振 飞秒抽运探测技术 信号强度     

2能级模型处理长脉冲圆偏振光与钠原子相互作用的合理性

 采用密度矩阵方法来处理长脉冲光与钠原子的相互作用,求解24能级钠精细结构的布洛赫方程,给出参与跃迁的每个态密度随时间的演化曲线。对于圆偏振情形,发现在长脉冲(大于100 ns)的持续时间内,最终的原子通过转移只在3S_1/2(2,2)到3P_/3/2(3,3)之间进行泵浦并且激发态达到稳态。进一步的2能级模型计算与24能级计算结果的对比表明：用2能级近似的速率方程方法取代24能级密度矩阵方法具有合理性,由此简化了模型,节约了后续研究的计算量。     

基于金属表面等离子激元控制光束的新进展

表面等离子激元(Surface plasmon polaritons,SPPs)是一种在金属-介质界面上激发并耦合电荷密度起伏的电磁振荡,具有近场增强、表面受限、短波长等特性,在纳米光子学的研究中扮演着重要角色。近年来表面等离子光学和基于SPPs的纳米光子器件的研究引起了国际上科学家们的广泛关注。讨论了SPPs的基本原理和在亚波长结构下的光学特性,介绍了基于亚波长金属结构的表面等离子激元在空间光束准直与聚焦、平面内光束聚焦与传导和在近场纳米光束的控制等方面的研究情况,以及在纳米光子学器件中的潜在应用。