双螺旋叠栅条纹检测光束准直性的两种方法

介绍双螺旋叠栅条纹检测光束准直性的基本原理,进一步就双螺旋叠栅条纹的特征参量与被测光束发散角(即光束准直精度)的关系进行分析和推导。在分析双螺旋叠栅条纹进行时,首先采用频域低通滤波提取纯叠栅条纹,然后提取纯叠栅条纹的特征参量。提出两种特征参量的提取方法,一种依次进行傅里叶变换计算相位信息的傅里叶变换方法,另一种是受传统时间相移算法启发而提出的空间相移算法,讨论了在两种方法中极坐标的重采样问题和相应的计算公式,并进行了计算机模拟。结果表明,傅里叶变换方法和空间相移算法实质都是获取叠栅条纹全场趋势的平均值,使最终光束发散角的检测具有很高的精度,对自成像条纹周期的检测误差在±2.8‰以内。     

基于二元光学设计的高能激光窗口的初步探讨

对非均匀近场强度分布影响强激光远场聚焦效果的原因进行了分析。对高能激光窗口进行了二元光学设计。提高了光束强度分布的均匀性,改善了光束质量。介绍了二元光学设计的基本原理,采用随机并行扰动爬山法对窗口的位相分布、变换后的光束强度分布、衍射效率和光束均匀性进行了计算。计算结果表明,基于二元光学设计的激光窗口能有效地改善光束强度分布的均匀性,提高了发射光束的质量。     

Low- x QCD physics from RHIC and HERA to the LHC

We present a summary of the physics of gluon saturation and non-linear QCD evolution at small values of the parton momentum fraction x in the proton and nucleus in the context of recent experimental results at HERA and RHIC. The rich physics potential of low-x studies at the LHC, especially in the forward region, is discussed and some benchmark measurements in pp, pA and AA collisions are introduced.     

Propagation of elliptical Gaussian beam passing through apertured paraxial optical systems

The propagation of elliptical Gaussian beam passing through paraxial optical systems with aperture is investigated analytically by using tensor method. The approximate formula for propagation of elliptical Gaussian beam through hard apertured optical systems is derived based on the fact that the circ function can be expanded into a finite sum of complex Gaussian functions. The derived formula provides a convenient tool for treating the propagation and transformation of elliptical Gaussian beam through apertured optical systems. As an application example, the propagation properties of elliptical Gaussian beam through apertured fractional Fourier systems are discussed.     

The backward phase flow and FBI-transform-based Eulerian Gaussian beams for the Schrödinger equation

We propose the backward phase flow method to implement the Fourier–Bros–Iagolnitzer (FBI)-transform-based Eulerian Gaussian beam method for solving the Schrödinger equation in the semi-classical regime. The idea of Eulerian Gaussian beams has been first proposed in [12]. In this paper we aim at two crucial computational issues of the Eulerian Gaussian beam method: how to carry out long-time beam propagation and how to compute beam ingredients rapidly in phase space. By virtue of the FBI transform, we address the first issue by introducing the reinitialization strategy into the Eulerian Gaussian beam framework. Essentially we reinitialize beam propagation by applying the FBI transform to wavefields at intermediate time steps when the beams become too wide. To address the second issue, inspired by the original phase flow method, we propose the backward phase flow method which allows us to compute beam ingredients rapidly. Numerical examples demonstrate the efficiency and accuracy of the proposed algorithms.     

皮秒脉冲功率技术理论模型及其优化设计

为了产生100~500 ps,200~500 kV,1~10 kA数量级的皮秒放电脉冲,建立了一个皮秒脉冲发生器理论模型,并提出利用增益系数极值法,确定其最大兼容工作点,相对于纳秒脉冲成形线,皮秒脉冲成形线实现了90%,70%,85%的归一化电压增益、能量增益和放电功率增益。为了最大限度地降低皮秒脉冲成形线的载压时间,提高系统的绝缘安全因子,利用华罗庚0.618优算法,设计了电压传输系数。在纳秒脉冲成形线与皮秒脉冲成形线阻抗比值等于1.63条件下,在4倍和6倍皮秒脉冲成形线时间之内,归一化电压增益、能量增益和放电功率增益就可以分别达到94%,72%,89%与99%,53%,97%。     

A novel optical beam splitter based on photonic crystal with hybrid lattices

A novel optical beam splitter constructed on the basis of photonic crystal(PC) with hybrid lattices is proposed in this paper.The band gap of square-lattice PC is so designed that the incident light is divided into several branch beams.Triangular-lattice graded-index PCs are combined for focusing each branch.Computational calculations are carried out on the basis of finite-different time-domain algorithm to prove the feasibility of our design.The waveguide is unnecessary in the design.Thus the device has functions of both splitting and focusing beams.Size of the divided beam at site of full-width at half-maximum is of the order of λ/2.The designed splitter has the advantages that it has a small volume and can be integrated by conventional semiconductor manufacturing process.     

Control of polarity and defects in the growth of AlN films on Si (111) surfaces by inserting an Al interlayer

We discuss the role of the Al interlayer in the suppression of pinhole formations and also look at the polarity transition of the AlN layers from N-polarity to Al-polarity when this Al interlayer is present. The AlN layers were grown by molecular beam epitaxy on an AlN nucleation layer. A thin Al interlayer was deposited on the initial nucleated AlN layer after the nitridation of the Al-soaked Si (111) substrates. The AlN layer with an Al interlayer showed a relatively smooth surface with a reduced density of pinholes compared with the AlN layer grown without an Al interlayer. In addition, the AlN layer with an Al interlayer showed some stacking faults in the interface between the Si substrate and the A1N layer. We also identify the polarity change of the AlN layer after the insertion of a thin Al interlayer from N-polarity to Al-polarity by chemical etching. A simple model is constructed to explain the polarity change and the pinhole suppression due to the Al interlayer.     

光学渡越辐射测量中能量分辨精度分析

 基于光学渡越辐射原理的用于高能强流电子束束流参数在线测量及诊断系统,具有时间响应快、分辨率高等特点,可以测量电子束的束剖面、发散角、能量等多个参数。分析了测量系统的结构参数（包括了透镜的焦距、成像面位置、CCD像元尺寸）对电子束能量测量精度的影响,并在理论上模拟了电子束的发散角的影响。还根据系统数据的特点,阐述了数据噪声对能量测量结果精度的影响,指出了光学渡越辐射测量中电子束能量分辨精度受到多种因素的影响,需要在数据处理时考虑修正。