Tunable ultranarrow linewidth of a cavity induced by interacting dark resonances

A scheme for obtaining a tunable ultranarrow linewidth of a cavity due to an embedded four-level atomic medium with double-dark resonances is proposed. It is shown that the steep dispersion induced by double-dark resonances in the transparency window leads to the ultranarrow transmission peak. Compared with the case of a single-dark resonance system, the linewidth can be narrowed even by one order under proper conditions. Furthermore, the position of the ultranarrow peak can be engineered by varying the detuning of the control field.     

The local-field corrective effect on Rabi oscillation of ultrashort pulse excitation in semiconductor GaAs

The Rabi oscillation of the thin bulk semiconductor GaAs, which takes into account the effect of the local-field correction induced by the interacting excitons, is investigated by numerically solving the semiconductor Bloch equations. It is found, for a 2π few-cycle pulse excitation, that two incomplete Rabi-floppings emerge due to the competition between the Rabi frequency of the incident pulse and the internal-field matrices. Furthermore, for a sub-cycle 2π pulse excitation a complete Rabi-flopping can occur because of the absolute phase effect. We ascribe these characteristics of the Rabi oscillation to the renormalized Rabi frequency.     

Direct observation of broadband conical emission along femtosecond-laser-induced rainbow filament in silver-nanoparticle-doped water

An experimental investigation is reported of conical emission (CE) along a femtosecond-laser-induced filament in water doped with sliver nanoparticles with a diameter of ～50?nm. In our experiment, the enhanced CE covers an extremely broad spectral range from 400?nm to 600?nm, which is directly observed from the side of the filaments. The finite-difference time-domain method is employed to calculate the localized surface plasmon resonance of one single 50?nm silver particle. The simulation result of the nanoparticle in the visible region agrees well with the observed spectral features of the supercontinuum generated during femtosecond laser filamentation.     

环形凹槽结构借助金属圆盘和金属锥尖实现增强聚束效应

基于传统“牛眼”结构对光波的聚束原理,介绍一种新颖的亚波长光聚束组合结构,在入射端的一定距离添加金属圆盘和出射端添加金属锥尖,实现聚柬能力的增强,FDTD仿真结果表明,基于金属圆盘和金属薄膜之间形成强烈共振的波导腔,使得远场光束中心能量增强 利用金属锥尖对出射光激发的表面等离激元进行局域和收集,抑制了远场光束的边锋,进一步增强了中心光束的能量,角分布变窄。该结构聚束作用和锥尖顶端局域场增强作用可广泛地应用于亚波长光学元器件设计、生物医疗探测等领域。     

Multi-synergy ablative effects of laminated SiO2–graphite/SiO2/Cu composite irradiated by high power laser

Faced with the challenge of ultra–high–temperature ablation problems, multi-synergy and efficient energy dissipation method is a feasible solution. A structure-modified silica-graphite composite with multiple copper layers was prepared by hot-pressing. The ablation behaviors and mechanisms were analyzed in detail. During the laser ablation, the designed composite exhibits excellent ablation resistance with a multi-synergy effects strategy. As ablation time increases, the ablation mechanisms change from reflection and horizontal thermal diffusion to reaction and horizontal thermal diffusion and vertical heat insulation. Moreover, the gap generated by the reaction volume contraction can further insulate against heat transfer in the vertical direction. The rate of increase of back-surface temperature can be further reduced. This multi-synergy effects strategy and designed structure accompanied with appropriate materials can greatly enhance the ablation resistance ability of the composite.     

载波包络相位稳定的6 fs超快强激光脉冲及其在高次谐波产生中的应用

脉冲宽度40 fs,功率1.1 W的载波包络相位(CEP)稳定的飞秒激光脉冲在充氩气的空芯光纤内由于自相位调制频谱展宽,通过啁啾镜和斜劈补偿色散,最终可获得脉冲宽度为6 fs的载波包络相位稳定的强激光脉冲.将之应用到高次谐波实验中得到了脉冲宽度为500 as的单个阿秒脉冲.     

Design of a [FeFe] macrocyclic metallotecton for light-driven hydrogen evolution reaction

Combining the two most fascinating fields of chemistry in the development of novel metal-organic architectures viz. macrocyclic chemistry and metallotectons, herein, we report the one-pot synthesis of a binuclear Fe(II) macrocyclic metallotecton 2 via coordination-driven assembly in excellent yield and purity. The single crystal structure of 2 indicates two units of cationic iron complex with ligand 1 (6- pyridin-2-yl- [1,3,5]-triazine-2,4-diamine) acting as metallotectons connected to each other by two [μ-PHO₃CH₃]^- bridges forming a [FeFe] macrocycle embedded in two metallotectons. The pyridine and DAT rings of both ligands 1 are nearly coplanar in 2 and each iron(II) has a distorted octahedral geometry. Diaminotriazine groups incorporated in 2 direct multiple hydrogen bonding according to predictable motifs II to produce a final three-dimensional structure. Thermal stability, electronic properties and redox properties of 2 have been studied by thermogravimetric analysis, UV–Vis and cyclic voltammetry respectively. The hydrogen evolution reaction (HER) study of 2 reveals it as an efficient photocatalyst displaying a high turnover number (TON) and turnover frequency (TOF), which is much higher than other Fe based molecular catalysts reported in literature. Also, its photocatalytic activity outperforms the most reported standard reference cobaloxime catalyst (Co^III(dmgH)₂(py)Cl). This is by far, the only report showcasing a macrocyclic metallotecton for photocatalytic HER. In addition, complex 2 can be regarded as the next level in supramolecular chemistry as it bridges the gap between macrocycles and metallotectons as well as it can be a future option for our deteriorating environment.     

双色场相位平缓对远场前向太赫兹的增强

太赫兹辐射极性和幅度依赖于双色场相位。由于等离子体光丝中色散和Gouy相移,导致双色场的相对相位随着激光的传播发生改变。当相位的改变量大于时,丝中的太赫兹电场极性发生反转,使得远场太赫兹辐射在离轴相位匹配角方向相干增强,而光轴前向相消减弱。通过对基频和倍频聚焦条件的调整和传输非线性色散的作用对双色场相对相位进行了调制,提出了可以使相对相位平缓的方法。模型计算证明了等离子体形成和Gouy相移调制是使双色场相移变平缓的原因。随后利用相位变平缓的条件得到了太赫兹发生极性反转的失相长度延长,最大长度近三倍于空气介质中的失相长度。在满足相位变平的条件下,远场太赫兹辐射在光轴前向的分布得到增强。     

Optical Instruments and Techniques

We experimentally demonstrate that significant enhancement of third harmonic generation during filamentation in air can be achieved by terminating a filament with either a pair of uncoated glass plates or a thin plasma string created by a second laser pulse. By comparing the results obtained under these two conditions, it appears likely that the inserted plasma string plays a role as a phase plate, by which the phase mismatch induced by the Gouy phase can be partially corrected.     

激光诱导材料表面着色研究进展

概述了三种激光着色机理:氧化膜干涉着色,以纳秒激光为主要着色方式,具有成本低、工业应用成熟等特点;周期性结构衍射着色,除了传统的超快激光诱导条纹结构着色,近些年发展起来的多光束干涉着色,丰富了周期性结构的种类,又大大提高了着色效率,更加适用于工业应用;等离基元金属纳米结构着色,通过调节纳米结构的间距、纳米结构尺寸等参数...