Stability and optoelectronic property of low-dimensional organic tin bromide perovskites

The toxicity and degradation of hybrid lead-halide perovskites hinder their extensive applications.It is thus of great importance to explore non-toxic alternative materials with excellent stability and optoelectronic property.We investigate the atomic structures and optoelectronic properties of non-toxic organic tin bromide perovskites(OTBP)with one/zerodimensional(1D/0D)structures by first-principles calculations.The calculated atomic structures show that the 1D/0D OTBPs are stable and the structure of inorganic octahedra in 0D is higher order than that in 1D.Moreover,the origination of exceptional purity emitting light in experiments is explained based on the calculated electronic structure.     

非平稳随机激励下系统首次穿越概率的近似解法

提出了非平稳Gausss白噪声激励下线性系统条件首次穿越概率的近似解析解.该近似解基于VanMarcke近似,但是,因为引进了随机过程和界限水平的标准化,VanMarcke公式中的期望衰减率可由响应的二阶统计矩获得,而不需要知道响应的相关函数或谱密度函数.给出了非平稳激励下线性系统响应的显式二阶统计矩.调制白噪声激励下单自由度线性系统的首次穿越概率分析说明了该方法的精度、效率和应用过程.     

Observation of single neutral atoms in a large-magnetic-gradient vapour-cell magneto-optical trap

Single caesium atoms in a large-magnetic-gradient vapour-cell magneto-optical trap have been identified. The trapping of individual atoms is marked by the steps in fluorescence signal corresponding to the capture or loss of single atoms. The typical magnetic gradient is about 29 mT/cm, which evidently reduces the capture rate of magneto-optical trap.     

卟啉衍生物的合成与性能研究进展

卟啉化学是有机化学研究中不可或缺的一个方向。由于卟啉在结构上具有一个大的共轭体系,从而具有典型的芳香性。其具有优异的光电性能、独特的光动力治疗作用、高效的催化活性,并且广泛存在于血红素、叶绿素、维生素B_(12)、过氧化氢酶等有机生物分子中,所有这一切都吸引着科学家们进行深入研究。本文从取代卟啉、缩合卟啉以及扩环卟啉三个方面分别讨论了卟啉的研究进展,通过列举一系列经典的反应以及卟啉衍生物,总结了卟啉衍生物的合成方法及其发展方向。另外,文中还对于卟啉的一些特殊物理、化学和光电性质,做了重点介绍。本文旨在为卟啉的研究者们提供参考。     

Interactive length of fundamental wave and second harmonic generated on the surface of anomalous dispersion medium

In this Letter, a new method is presented to calculate the interactive length between the fundamental wave and second harmonic generation(SHG) for the configuration of total internal reflection on the inner surface of a nonlinear crystal. Three independent experiments are designed to measure the bandwidths of this second harmonic wave. The theoretical expression of the intensity of SHG is obtained through a nonlinear coupled wave equation. The interactive length of this phase-matched SHG can be calculated mathematically by utilizing the measured bandwidths and the intensity equation. There is no existing method to obtain the interactive length either from theoretical calculations or by experimental measurement. This method can be applied to estimate the extremely short interactive volume in nonlinear processes.     

Photodetecting and light-emitting devices based on two-dimensional materials

Two-dimensional(2D) materials, e.g., graphene, transition metal dichalcogenides(TMDs), and black phosphorus(BP), have demonstrated fascinating electrical and optical characteristics and exhibited great potential in optoelectronic applications. High-performance and multifunctional devices were achieved by employing diverse designs, such as hybrid systems with nanostructured materials, bulk semiconductors and organics, forming 2D heterostructures. In this review,we mainly discuss the recent progress of 2D materials in high-responsive photodetectors, light-emitting devices and single photon emitters. Hybrid systems and van der Waals heterostructure-based devices are emphasized, which exhibit great potential in state-of-the-art applications.     

Deterministic loading of an individual atom:Towards scalable implementation of multi-qubit

We report the realization of a deterministic single-atom preparation by the method of all-optical feedback. Using a fast-real-time feedback, the light-induced atom desorption effect and blue detuned light-induced atom collision process can increase a success probability of single-atom preparation up to more than 99%. We investigate the dynamics of loading single atom trapped in a trap with a size of hundreds of micrometers into a pair of microscopic tweezers. The detailed experimental results show that the feedback loading is spatially insensitive, which implies that it is possible to use the feedback protocol to simultaneously implement the loading of large number of qubits arrays.     

低分析频率压缩光的实验制备

基于PPKTP晶体的阈值以下光学参量振荡(OPO)过程,制备了共振于铷原子D1线795 nm的压缩真空态光场,研究了分析频率处于千赫兹范围的主要噪声来源,特别是795 nm激光及其二次谐波397.5 nm激光在晶体内吸收引起的非线性损耗增加和系统热不稳定的问题(397.5 nm激光处于PPKTP晶体透光范围边缘,具有高于其他波长数倍的吸收系数).以795 nm和1064 nm为例,分析了非线性损耗及晶体内热效应对压缩度的影响.受限于以上因素,795 nm压缩光很难得到1064 nm波段同样的压缩度.探测系统中的噪声耦合则限制了压缩频带.实验上对分析频率为千赫兹的经典噪声进行了有效控制,通过使用真空注入的OPO、垂直偏振及反向传输的腔长锁定光、低噪声的平衡零拍探测器、高稳定度的实验系统及量子噪声锁定等方法,最终在2.6—100 kHz的分析频段得到了约2.8 dB的795 nm压缩真空.该压缩光可用作磁场测量系统的探测光以提高测量灵敏度.     

Saturable Absorption Enchantment of Au Nanorods Based on Energy Transfer between Longitudinal and Transverse Energy Levels

Four kinds of Au nanorods(NRs)with different aspect ratios are designed to adjust the relationship between resonance energy level of longitudinal(L)and transverse(T)modes.During the femto-second Z-scan experiments,huge saturable absorption phenomena are observed while the energy level T is located between one to two times of the energylevel L.This means that the energy may transfer between longitudinal and transverse energylevels in the same and/or different Au NRs.It effectively depresses the production of revised saturated absorption and increases the saturable absorption efficiency.This method is significant for the preparation of high-efficiency saturable absorption devices.     

Calculating the dielectric anisotropy of nematic liquid crystals: a reinvestigation of the Maier——Meier theory

This paper investigates the average dielectric permittivity (\overline ε ) in the Maier--Meier theory for calculating the dielectric anisotropy (Δε) of nematic liquid crystals. For the reason that \overline ε of nematics has the same expression as the dielectric permittivity of the isotropic state, the Onsager equation for isotropic dielectric was used to calculate it. The computed \overline ε shows reasonable agreement with the results of the numerical methods used in the literature. Molecular parameters, such as the polarizability and its anisotropy, the dipole moment and its angle with the molecular long axis, were taken from semi-empirical quantum chemistry (MOCPAC/AM1) modeling. The calculated values of Δε according to the Maier--Meier equation are in good agreement with the experimental results for the investigated compounds having different core structures and polar substituents.