Shanghai Institute of Optics and Fine Mechanics,Chinese Academy of Sciences
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Collective Deceleration of Laser-Driven Electron Bunches
No full textCluster of Excellence MAP [EXC158]; DFG Project [Transregio TR18]; Euratom research and training programme [633053]; Max- Planck-SocietyFew-fs electron bunches from laser wakefield acceleration (LWFA) can efficiently drive plasma wakefields (PWFs), as shown by their propagation through underdense plasma in two experiments. A strong and density-insensitive deceleration of the bunches has been observed in 2 mm of 10(18) cm(-3) density plasma with 5.1 GV/m average gradient, which is attributed to a self-driven PWF. This observation implies that the physics of PWFs, usually relying on large-scale rf accelerators as drivers, can be studied by tabletop LWFA electron sources
Color Difference Analysis of Femtosecond Laser Colorized Metals
No full text利用飞秒激光聚焦辐照金属表面可以诱导出亚波长周期结构,从而实现金属表面着色.改变照明光入射角和样品水平旋转角,金属表面结构色的色调和亮度均发生变化,这说明结构成色具有方向性.为探究飞秒激光在金属表面着色的均匀性,基于国际光学照明委员会关于颜色差的规定对成色的偏差作了分析,结果表明,样品加工面积越大,颜色的均匀性越差.在设定的实验参数下,当样品加工面积达到64mm~2时,其边缘与中心颜色的差异可以被人眼明显察觉.通过制作两个彩色图标来展示结构色的方向性和均匀性对飞秒激光彩色标记实际应用的影响.国家自然科学基金Femtosecond lasers focused on metal surfaces can induce subwavelength periodic structures,which can make metal surfaces colorize.The hue and brightness of the structural colors vary with the incident angle of illumination and sample rotation angle,which indicates the structural color has directional property.In order to investigate the uniformity of femtosecond laser colorization on metal surfaces,based on the color system of International Commission on Illumination the color deviation is analyzed.The results show that the larger the processing area is,the worse the color uniformity is.With the specified experimental parameters,when the processing area of sample reaches to 64 mm~2,the difference between edge color and center color is obvious to human eyes.Two colorized icons are made to demonstrate the effects of the directionality and uniformity of structural colorization on the practical application of femtosecond laser color marking
Control of transmission of right circularly polarized laser light in overdense plasma by applied magnetic field pulses
No full textNational Natural Science Foundation of China [11475147, 11374262, 11304331, 11174303]; National Basic Research Program of China [2013CBA01504, 2011CB808104]; State Key Laboratory of High Field Laser Physics at SIOM; Fundamental Research Funds for CentralThe effect of a transient magnetic field on right-hand circularly polarized (RHCP) laser light propagation in overcritical-density plasma is investigated. When the electron gyrofrequency is larger than the wave frequency, RHCP light can propagate along the external magnetic field in an overcritical density plasma without resonance or cutoff. However, when the magnetic field falls to below the cyclotron resonance point, the propagating laser pulse will be truncated and the local plasma electrons resonantly heated. Particle-in-cell simulation shows that when applied to a thin slab, the process can produce intense two-cycle light pulses as well as long-lasting self-magnetic fields
Design and application of Nd: Glass disc-amplifier as pump source of 5 PW Ti: Sapphire chirped pulsed amplifier
No full text基于蒙特卡罗光线追迹法,进一步研究了钕玻璃片状放大器三维空间聚光腔抽运分布的数值模拟。并且,结合氙灯的充放电回路及辐射光谱、放大自发辐射、以及激光脉冲受激辐射放大等相关数值计算模块,实现了片状钕玻璃放大器由储能至放大的整个过程的动态数值仿真。基于该数值模拟结果,设计研制的钕玻璃片状放大器已用于5PW钛宝石啁啾脉冲放大器的抽运源中,其实验输出结果与数值计算结果基本一致。国家自然科学基金(61378083,61521093)Based on the Monte Carlo rays tracing method, the three dimensional numerical model of pump distribution in Nd: glass disc amplifier is developed. In addition, combined with the other numerical models of Xe flashlamp charge/discharge circuit, amplified spontaneous emission, and laser pulse amplification, the whole work process of Nd: glass disc-amplifier is numerical simulated in detail to realize the whole process of the energy storage to the amplifying of Nd: glass disc amplifier. Based on the results of numerical simulation, the designed Nd: glass disc amplifier is used in the experiments of 5 PW Ti: sapphire chirped pulse amplifier, and the experimental results are in good accordance with the calculated consequence. ? 2016, Chinese Lasers Press. All right reserved
Experimental demonstration of broadband femtosecond optical parametric amplification based on YCOB crystal at near critical wavelength degeneracy
No full textNational Basic Research Program of China [2011CB808101]; National Natural Science Foundation of China [61078037, 11127901, 11134010, 61205208, 11204328]Broadband optical parametric amplification (OPA) in the near-infrared region (1.3-1.8 mu m) is demonstrated in YCOB crystal pumped by 1 kHz Ti:sapphire based femtosecond laser at near critical wavelength degeneracy phase matching condition at first time. The gain bandwidth is closed to BIBO or BBO crystal OPA gain bandwidth. The energy obtained with 3.5 mm-thick YCOB reached 20 pj with RMS 1.9%. After second harmonic generation, 17.6 fs pulse is obtained, and the pulse compressibility is demonstrated. (C) 2016 Elsevier B.V. All rights reserved
Frequency control of the broadband ultrashort terahertz source generated from the laser induced plasma by two-color pluses
No full text实验研究了双色超快强激光场作用于氮气分子束所产生的宽带太赫兹(THz)辐射光谱随等离子体介质的密度和长度的依赖关系, 发现THz辐射的中心频率随等离子体密度提高和长度减小而增大(0.8-1.4 THz), 且谱宽也随之增加(0.78-1.53 THz). 分析和计算表明, 太赫兹光谱的变化由等离子体振荡频率和谱宽决定. 该发现为等离子体宽带太赫兹辐射源的光谱操控提供了新思路.National Natural Science Foundation of China [11274326, 61521093, 61405222, 11134010, 11127901]; National Basic Research Program of China [2011CB808103]The terahertz (THz) radiation becomes an attractive light source utilized in molecular dynamic spectroscopy, remote sensing, medicine, communication and fundamental research. The controlling of the THz spectrum is necessary for the applications. In this paper, a method is proposed for controlling the terahertz spectra generated from the laser induced plasma by two-color pluses based on the contribution of plasma oscillation. The plasma current oscillation can shift the THz spectrum when the length of medium is less than plasma skin depth. Experimentally we use a short length of molecules by means of the molecular beam method. We investigate the changing spectrum of broadband ultrashort terahertz THz generated from a jet of nitrogen (N-2) molecules pumped with the two-color laser pulses following the varying plasma density and plasma length. With the increase of plasma density and the decrease of the plasma length, we observe the increase of THz central frequency (0.8-1.4 THz) and the broadening of the THz spectral width (0.78-1.53 THz). The analysis and the calculation show that the THz spectrum changes due to the frequency and the width of the plasma resonance. This scheme of controlling the THz spectrum by changing the plasma density and length is easier to implement and do not need to use complex shaped optical pulses. The discovery provides a new way of controlling the low-frequency broadband THz spectrum
High contrast amplification at 1053 nm limited by pulse stretching-compressing process
No full textWe report on our high-contrast laser based on high-contrast, high-energy seed injection, low-gain optical parametric chirped pulse amplification (OPCPA), and Nd:glass amplifiers, which can be used as the high-contrast front end of a high-power Nd:glass chirped pulse amplification (CPA) laser system. The energy of the stretched 1053 nm high-contrast seed pulse increases to 60 mu J by optimizing the frequency doubling crystal in the pulse cleaning device. After passing through a two-stage low-gain OPCPA, a 2-pass 2-rod Nd:glass amplifier, and a compressor the amplified pulse of 131 mJ/282 fs is achieved. The third-order correlation scanning measurement shows that the pulse contrast in the tens of ps range is about 10(-7)-10(-8). With the high-contrast seed passing through the stretcher and compressor only, the contrast measurement indicates that the stretching-compressing process leads mainly to the contrast degradation of the amplified pulse
Inner Shell Excitations through Laser Induced Electron Recollision
No full textSub-femtosecond excitation of inner-shell electrons is a prerequisite step toward time domain "pump-probe" study of core-hole dynamics. By using a few cycles 1800nm source, we show that the recolliding electron might provide this necessary step
Lasing in strong-field ionized nitrogen molecules: influence of nuclear dynamics on population inversion
No full textWe investigate nuclear dynamics and population transfer among multiple electronic states in tunnel ionized nitrogen molecules, and clarify the underlying mechanism behind the population inversion responsible for free-space N2(+) lasers
Manipulation of tribological properties of stainless steel by picosecond laser texturing and quenching
No full textNational Natural Science Foundation of China [61178024, 11374316]We reported on the manipulation of tribological properties of stainless steel by picosecond laser texturing and quenching. The micro-grooved textures were formed on the steel surface, accompanied with the appearance of nanostructures with grain sized of 80-400 nm, oxides thin film (Fe2O3 and Cr2O3) and martensite during picosecond laser surface texturing process. The tribological tests indicated that the average friction coefficients and wear rates of textured surfaces initially increased then decreased with the increase of spacing of micro-grooves. The well-controlled friction and wear properties are attributed to the combined effects of induced micro-/nanostructures, martensitic transformation and oxides thin film in the local quenched zone of stainless steel samples. (C) 2016 Elsevier Ltd. All rights reserved