High-dispersive mirror for pulse stretcher in femtosecond fiber laser amplification system

We present a high-dispersive multilayer mirror for pulse stretching in a femtosecond fiber laser amplification system. The designed mirror contains 54 layers with a total physical thickness of 7.3 μm, which can provide a positive group delay dispersion (GDD) of 600 fs² and a high reflectance over 99.9% from 1010 to 1070 nm. The samples were prepared by dual ion beam sputtering. The measured transmittance matches well with the theoretical result. The GDD characteristics of samples were tested by home-made white light interferometer. The measured GDD is higher than the design results, an average GDD of +722 fs² from 1010 nm to 1070 nm. The mirrors were employed in a Yb-doped large-mode-area photonic crystal fiber amplification system. An input pulse compressed by the gratings with autocorrelation function of 83 fs is obtained with a stretched FWHM of 1.29 ps after 28 bounces between the dispersive mirrors. The results show that the multilayer dispersive mirror could be an effective and promising technique for pulse stretching in femtosecond amplification systems.     

Real-time tomographic reconstructor based on convolutional neural networks for solar observation

Solar observation is the branch of astronomy devoted to the study of the Sun. When the light wavefront that comes from the Sun penetrates the atmosphere, it suffers some distortions caused by optically turbulent layers that change the wavefront's shape and morphology. Therefore, in order to obtain a good-quality image, it is necessary to correct the induced error. This is done by applying adaptive optics (AO) techniques. In the case of the present research, it is performed with the help of a Single Conjugate Adaptive Optics System (SCAO). The reconstruction technique proposed in this research is a SCAO based on convolutional neural networks (CNNs). This research develops and assesses a real-time tomographic reconstructor based on CNN, able to correct the error introduced by the atmosphere in the light wavefront received from the Sun. The CNN was trained and validated using data from the Durham AO Simulation Platform as input information. This platform incorporates certain solar functionalities that have been employed in the present research, allowing us to simulate a solar telescope. The normalized errors obtained for both ReLu and Leaky ReLu kernels were promising, without showing statistically significant differences among kernels in the value of RMSE volts of the deformable mirror commands. When different kernel dimensions are compared, statistically significant differences are found, showing that RMSE volts of the deformable mirror commands are lower for 3 × 3 kernels when compared with those of dimensions 5 × 5 and 7 × 7. As far as the authors know, this is the first time that an AO system based on CNN has been developed for solar telescopes.     

Stresses in rotating heterogeneous viscoelastic composite cylinders with variable thickness

An analytical solution is presented for the rotation problem of a two-layer composite elastic cylinder under a plane strain assumption. The external cylinder has variable-thickness formulation, and is made of a heterogeneous orthotropic material. It contains a fiber-reinforced viscoelastic homogeneous isotropic solid core of uniform thickness. The thickness and elastic properties of the external cylinder are taken as power functions of the radial direction. By the boundary and continuity conditions, the radial displacement and stresses for the rotating composite cylinder are determined. The effective moduli and Illyushin’s approximation methods are used to obtain the viscoelastic solution to the problem. The effects of heterogeneity, thickness variation, constitutive, time parameters on the radial displacement, and stresses are investigated.     

用磁探针反演磁岛二维结构的方法及其在HL-2A装置上的应用

介绍了HL-2A装置中利用磁探针数据反演磁岛极向二维结构的新方法,以及在反演基础上建立的撕裂模动态分析方法。在实验中通过磁探针测量确定作为扰动磁场来源的扰动电流。将扰动磁通与由EFIT重建的平衡磁通叠加反演出磁岛的结构,并给出磁岛的宽度。然后,按时间顺序建构二维结构图并依次记录,之后依次展现图像就可以对磁岛进行动态分析。应用此方法进行撕裂模分析,得出了磁岛旋转与电子抗磁漂移方向相同,验证了磁岛宽度与扰动场的关系及ECRH对磁岛的抑制作用。这显示了磁探针反演磁岛结构方法的直观性,对观察并控制MHD不稳定性非常有利。     

旋转薄板的一种高次动力学模型与频率转向

对固结于转动刚体上柔性薄板的刚柔耦合动力学和频率转向特性进行了深入研究,建立了系统的高次刚柔耦合动力学模型,该动力学模型计入了由于横向变形而引起的面内纵向缩短项,即非线性耦合变形量,并且完整保留了与非线性耦合变形量相关的所有项. 研究表明,高次耦合模型不仅适用于小变形问题,而且还适用于大变形问题,弥补了一次近似耦合模型在处理大变形问题上的不足. 旋转悬臂薄板相邻两阶模态间既有柔和的频率转向现象也有剧烈的频率转向现象. 柔和的频率转向伴随着的振型转换的过程是连续的,而剧烈的频率转向伴随着的振型转换的过程则是不连续的. 相隔多阶模态间存在传递性频率转向,并伴随着振型转移.      

探究不同银配合物对银镜反应的影响

为探究配体与银形成不同银配合物对银镜反应的影响,以氨水、乙二胺、硫氰化钾和甲胺为配体,通过利用不同银配合物的稳定常数研究不同温度条件下银镜反应的情况,对银镜形成时间和质量做比较。结果表明,在这4种配体中,以乙二胺为配体形成的银配合物稳定常数较高,且碱性较强,室温条件下能快速形成高质量的银镜,利于课堂上开展银镜反应实验演示教学。     

19-fs pulse generated by supercontinuum compression

Supercontinuum generation and compression in a length of 50-mm photonic crystal fiber with pulse of nanojoule energy are investigated theoretically and experimentally. Chirped mirror pair is used for dispersion compensation and pulse compression. Pulse characteristics are measured by frequency-resolved optical gating. And 19-fs pulse is generated.     

Alternating-current relaxation of a rotating metallic particle

Based on a first-principles approach,we establish an alternating-current(AC) relaxation theory for a rotating metallic particle with complex dielectric constant ε_α=ε_α-iσ_α/ω_0.Here εα is the real part,σ_α the conductivity,ω_0 the angular frequency of an AC electric field,and i=-1~(1/2).Our theory yields an accurate interparticle force,which is in good agreement with the existing experiment.The agreement helps to show that the relaxations of two kinds of charges,namely,surface polarized charges(described by ε_α) and free charges(corresponding to σ_α),contribute to the unusually large reduction in the attracting interparticle force.This theory can be adopted to determine the relaxation time of dynamic particles in various fields.     

Massive Vector Particles Tunneling from the Neutral Rotating Anti-de Sitter Black Holes in Conformal Gravity

We investigate the massive vector particles' Hawking radiation from the neutral rotating Anti-de Sitter(AdS) black holes in conformal gravity by using the tunneling method.It is well known that the dynamics of massive vector particles are governed by the Proca field equation.Applying WKB approximation to the Proca equation,the tunneling probabilities and radiation spectrums of the emitted particles are derived.Hawking temperature of the neutral rotating AdS black holes in conformal gravity is recovered,which is consistent with the previous result in the literature.     

银镜反应实验条件优化的研究性学习活动及行为分析

选择银镜反应实验优化条件为研究性学习活动,阐述了活动目标、实施步骤、银镜反应的正交设计、实验过程及结论。利用NVivo 10.0质性分析工具,对上述活动进行质性分析,阐述了研究过程以及利用NVivo 10.0质性分析工具获得的结论。