Shanghai Institute of Optics and Fine Mechanics,Chinese Academy of Sciences
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Picosecond laser-induced water condensation in a cloud chamber
No full textNational Natural Science Foundation of China [11425418, 61475167, 11404354, 61221064]; Shanghai Science and Technology Talent Project [12XD1405200]; State Key Laboratory Program of the Chinese Ministry of Science and Technology; Talent Program of ChineseWe investigated water condensation in a laboratory cloud chamber induced by picosecond (ps) laser pulses at similar to 350 ps (800 nm/1-1000 Hz) with a maximum peak power of similar to 25 MW. The peak power was much lower than the critical power for self-focusing in air (similar to 3-10 GW depending on the pulse duration). Sparks, airflow and snow formation were observed under different laser energies or repetition rates. It was found that weaker ps laser pulses can also induce water condensation by exploding and breaking down ice crystals and/or water droplets into tiny particles although there was no formation of laser filament. These tiny particles would grow until precipitation in a super-saturation zone due to laser-induced airflow in a cold region with a large temperature gradient. (C) 2016 Optical Society of Americ
Strong Spatial Confinement of Terahertz Wave inside Femtosecond Laser Filament
No full textNational Basic Research Program of China [2014CB339802, 2014CB339806]; National Natural Science Foundation of China [11574160]; Major National Development Project of Scientific Instrument and Equipment [2012YQ150092, 2012YQ14000504]; Tianjin Research Program of Application Foundation and Advanced Technology [15JCZDJC31700]; Shanghai Subject Chief Scientist [14XD1403000]; Shanghai Basic Research Key Project [14DZ1206600]; State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics (SIOM)In this paper, a new experimental phenomenon is demonstrated. During the femtosecond laser filamentation, the generated terahertz (THz) pulse has been found to be strongly confined inside the plasma channel, reaching a spatial diameter of a few tens of micrometers. It has been attributed to the formation of a plasma negative dielectric waveguide induced by the transverse inhomogeneous plasma density distribution. The new experimental phenomenon will renew the understanding of the THz wave generation and propagation dynamics during the femtosecond laser and air plasma interaction. Due to this strong spatial confinement, THz electric field strength could be enhanced by orders of magnitude, potentially providing a new approach to performing THz nonlinear optics with low laser energy
Ultrafast Laser Annealingof Semiconductors
No full text脉冲激光退火技术从1974年问世以来一直被认为是一种热处理方式。皮秒范围内的超短脉冲退火可以用热模型解释。飞秒或脉宽更短的超短脉冲激光可以直接通过电子激发来实现晶格结构的改变,在低于熔点的情况下完成退火。超短脉冲激光退火属于非热模型退火,是一种新型的退火方式。主要介绍了两种退火模型的基本原理,概括了超短脉冲激光退火发展的历史和现状,并分析了其未来的研究趋势。国家自然科学基金The technique that intense laser pulses is used to anneal the lattice has been established a thermal process since it was discovered in 1974.The thermal model works well for any material that is excited with picosecond or longer-duration laser pulses.For femtosecond and shorter-duration laser pulses,however,the lattice structural changes can be driven directly by electronic excitation.This means that annealing can be completed under melting point.The ultrashort laser pulse annealing is a non-thermal process and it is a new way of annealing.This review focuses on the nature of thermal and non-thermal models.The history,current situation,and the trend of ultrashort laser pulse annealing are also summarized
Highly reliable optical system for a rubidium space cold atom clock
No full textNational Natural Science Foundation of China (NSFC) [11034008]; Ministry of Science and Technology of the People's Republic of China (MOST) [2013YQ09094304]; Youth Innovation Promotion Association of the Chinese Academy of SciencesWe describe a highly reliable optical system designed for a rubidium space cold atom clock (SCAC), presenting its design, key technologies, and optical components. All of the optical and electronic components are integrated onto an optimized two-sided 300 mm x 290 mm x 30 mm optical bench. The compact optical structure and special thermal design ensure that the optical system can pass all of the space environmental qualification tests including both thermal vacuum and mechanical tests. To verify its performance, the optical system is carefully checked before and after each test. The results indicate that this optical system is suitably robust for the space applications for which the rubidium SCAC was built. (C) 2016 Optical Society of Americ
Measuring magnetic field vector by stimulated Raman transitions
No full textNational Natural Science Foundation of China [11404353, 91336105, 61275204]We present a method for measuring the magnetic field vector in an atomic fountain by probing the line strength of stimulated Raman transitions. The relative line strength for a A-type level system with an existing magnetic field is theoretically analyzed. The magnetic field vector measured by our proposed method is consistent well with that by the traditional bias magnetic field method with an axial resolution of 6.1 mrad and a radial resolution of 0.16 rad. Dependences of the Raman transitions on laser polarization schemes are also analyzed. Our method offers the potential advantages for magnetic field measurement without requiring additional bias fields, beyond the limitation of magnetic field intensity, and extending the spatial measurement range. The proposed method can be widely used for measuring magnetic field vector in other precision measurement fields. (C) 2016 AIP Publishing LLC
Arrangement of Beam-Guiding System in Target Area of Laser Driver
No full text靶场光路导引系统(BGS)具有两个功能,一是将主激光的列阵排布转变为满足打靶激光要求的球形辐照结构,二是保证所有光路等光程传输到靶室中心。主要研究了主激光和打靶激光的传输模型以及它们之间的编组方式。结合靶室入射法兰口分布的对称特性,提出传输子单元概念来简化系统的排布。首先,综合考虑反射镜的种类和数量以及靶场的空间大小,确定传输子单元的具体模型以及靶场的对称划分方式。再根据激光偏振态和光路无交叉限制,得到主激光和打靶激光两种可能的传输模型。通过分层定基线算法,结合物像传递关系,确定具体的编组方式,从而最终得中以惯性约束聚变能源先期关键技术合作研究Beam-guiding system (BGS) has two functions, one shifts the array arrangement of the main laser to the spherical irradiation structure which meets the requirements of shooting laser, the other ensures that all the laser beams transmit to the target chamber center with the same light path length. Main issues are focused on the transmission models of the main lasers and shooting lasers and the switch manner between them. Combining the symmetric properties of the beam port distribution on the target chamber, the transmission sub-unit is proposed to simplify the system arrangement. Firstly, considering the quantity and style of the total mirrors and the space size of the target area, the specific transmission models in a transmission sub-unit and the symmetrical division of target area are determined. Then, two possible transmission models for main lasers and shooting lasers are obtained with the constraints of laser polarization and no intersection among beams during propagation. The switch manner is calculated with a stratified baseline algorithm and the relationship between the image and object of the propagation lasers. In this manner, the entire BGS geometric arrangement is figured out
Spectrum Control Based on All-Fiber Multi-Pass Phase Modulation Structure
No full text提出了一种基于全光纤多程相位调制的光谱控制方法,并对其进行了理论模拟和实验研究。理论模拟结果表明,调制次数、调制深度、调制信号形状和宽度以及调制信号和光脉冲的时间同步均会对输出光谱的中心波长、光谱宽度和形状产生影响。在实验上对光谱宽度为0.03 nm的注入信号进行多程相位调制,得到了带宽为2.238 nm的输出光谱,实验结果与理论模拟结果相符合。并从实验上研究了不同相位调制信号波形与输出光谱的对应关系,验证了通过控制调制信号波形进行光谱特性控制的可行性。国家自然科学基金A method of controlling spectrum based on all-fiber multi-pass phase modulation is demonstrated experimentally and theoretically. Numerical simulation results indicate that modulation times, modulation depth, shape and width of the modulation signal and synchronized precision between optical pulse and modulation signal have influences on the central wavelength, bandwidth as well as the shape of the output spectrum. The input spectrum with bandwidth of 0.03 nm is broadened into 2.238 nm after multi-pass phase modulation, and the experimental results match well with the simulation results. The corresponding relationship between the modulation signal waveforms with different phases and the output spectra is obtained, and the feasibility of the spectral characteristics control is verified
光学系统的光束指向稳定性光电测试法研究
No full text从振动的基本理论出发,应用矩阵光学理论,推导了光学图像法测试光束指向稳定性的原理。设计了光电法测试光束指向稳定性的测试应用,并搭建了实验光路,结果表明:光学图像法可以准确分析光束指向稳定性误差的大小、产生的误差的振动频率及其影响程度,并结合加速度计的电学法测试,可以探测光路中引起光束指向误差的来源。光电法测试结果正确可靠、简单方便,具有较好的工程应用价值,特别适合大型光学系统的光束指向稳定性测试
Damage morphology and mechanism in ablation cutting of thin glass sheets with picosecond pulsed lasers
No full textWe experimentally investigated the morphology and mechanism of laser-induced damage in the ablation cutting of thin glass sheets with picosecond pulsed lasers and we compared the experimental results to our models. After several passes of laser ablation, we observed two different kinds of damage morphologies on the cross-section of the cut channel. They are distinguished to be the damage region caused by high-density free-electrons and the heat-affected zone due to the heat accumulation, respectively. Furthermore, micro-cracks can be observed on the top surface of the workpiece near the cut edge. The nano-cracks could be generated by high energy free-electrons but opened and developed to be visible micro-cracks by thermal stress generated in the heat-affected zone. The crack length was proportional to the volume of heat-affected zone. Heat-affected-zone and visible-cracks free conditions of glass cutting were achieved by controlling the repetition rate and spatial overlap of laser pulses. (C) 2016 Elsevier Ltd. All rights reserved
Light intensity distribution of high-power laser beams on target plane under different focus system of 2 x 2 beam array
No full text大口径高功率激光装置为提高激光靶面的光强强度,通常采用2*2集束聚焦的模式进行打靶.大口径楔形透镜是组成2*2集束聚焦系统的核心元件,可分为二维离轴楔形透镜、一维离轴楔形透镜和非离轴楔形透镜3类.为了获得理想靶面光强分布,基于这3类楔形透镜,对比研究相应2*2集束聚焦系统下的靶面光强分布特性.研究结果表明:相比离轴楔形透镜,采用基于非离轴楔形透镜的2*2集束聚焦系统时,容易在激光靶面获得更窄的主瓣宽度、更强的峰值强度、更高的能量集中度.研究结果对高功率激光靶场聚焦系统的配置选择有重要参考价值.National Natural Science Foundation of China [60707019]Large aperture high-power laser drivers usually focus the high power laser beams in 2 x 2 quads to the target chamber center in order to increase the light intensity on the target plane. The large aperture wedged focus lenses are the core components in the focus system of quadruplets of beams, and it is thought possible to use four two-dimensional off-axis wedged focus lenses as four sub-lenses to make up a larger aperture wedged focus lens in form to focus the four beams. Given that the large aperture two-dimensional off-axis wedged focus lenses are processed and used difficultly, the wedged focus lenses are divided into three categories: the two-dimensional off-axis wedged focus lenses, the one-dimensional off-axis wedged focus lenses, and the non-off-axis wedged focus lenses. On the basis of the three modes of the wedged focus lenses and the corresponding specific incidence angles of each sub-beam, the three focus schemes for the 2 x 2 beam array are put forward to comparatively research the light intensity distribution on the target plane. Research results show that from a perspective of the coherence among the four sub-beams, the phase factors of each sub-beam respectively introducing by the three focus systems with the two-dimensional off-axis, one-dimensional off-axis, and non-off-axis wedged focus lenses are asymmetric, asymmetric and symmetric inside each sub-beam, and symmetric, asymmetric and symmetric among the four sub-beams. Therefore, the wave front consistency of the four sub-beams decreases in the order of the focus systems with the non-off-axis, two-dimensional off-axis, and one-dimensional off-axis wedged focus lenses. The focus schemes with the non-off-axis wedged focus lenses for 2 x 2 beam array can get the narrowest main-lobe, the strongest peak-value intensity, the highest energy concentration ratio on the target plane, followed by the one-dimensional off-axis and two-dimensional off-axis wedged focus lenses. The off-axis mode of the wedged focus lenses not only increases the complexity in the course of processing and using, but also increases the main-lobe size, decreases the peak-value intensity and the energy concentration ratio, which obtains a weaker focusing characteristics than that of the non-off-axis mode of the wedged focus lenses. Research results can provide an important reference for the design of the focus system in the target area of high-power laser drivers