1南开大学现代光学研究所天津市微尺度光学信息技术科学重点实验室, 天津 300350
超快激光成丝是高功率超快激光在透明光学介质中传输时出现的一种独特非线性光学现象,所产生长度远超共焦范围的离子体通道被称为光丝;同时伴随超连续谱产生、荧光辐射和受激放大、脉冲自压缩等丰富的光学效应,在大气遥感、超快激光技术、人工干预天气、激光超精细加工等方面具有广泛应用前景。本文对成丝现象研究的历史发展进行了简单介绍,包括实验技术、基本物理机制和调控方法的主要研究进展,并对成丝在大气远程应用、物理化学机制、强THz波产生等方面的研究所面临的挑战进行了展望。
激光光学 超快激光 非线性光学 激光成丝 超快激光现象
1 中国科学院上海光学精密机械研究所强场激光物理国家重点实验室, 上海 201800
2 中国科学院大学, 北京 100049
3 上海交通大学聚变科学与应用协同创新中心, 上海 200240
4 上海师范大学物理系, 上海 200234
5 中国科学院大气物理研究所中层大气和全球环境探测重点开放实验室, 北京 100029
6 拉瓦尔大学光学、光子学和激光研究中心, 加拿大 魁北克市 G1V 0A6
在室温条件下的小型云室中,研究了不同参数对飞秒激光诱导较大尺寸气溶胶生成的影响。实验结果表明,在亚饱和条件下,随着环境相对湿度的提高,不同尺寸气溶胶的数密度增大,尺寸分布以0.3~0.5 μm为主;当环境相对湿度达到近饱和条件时,较大尺寸(直径D≥0.7 μm)气溶胶的数密度显著增大,1.0~2.0 μm气溶胶与0.3~0.5 μm气溶胶的数密度可相比拟。此时,通过延长激光照射时间或者缩紧激光聚焦条件,不同尺寸气溶胶的数密度可同等程度地增大,尺寸分布规律基本不变。理论分析结果表明,环境相对湿度条件是制约飞秒激光诱导较大尺寸气溶胶生成的关键因素。
超快光学 非线性光学 飞秒光丝 气溶胶 光化学反应
Author Affiliations
Abstract
1 Department of Physics, Shanghai University, Shanghai 200444, China
2 State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China
3 Centre d’Optique, Photonique et Laser (COPL) and Département de physique, de génie physique et d’optique, Université Laval, Québec, Québec G1V 0A6, Canada
We report on a systematic study of the laser polarization effect on a femtosecond laser filamentation in air. By changing the laser’s ellipticity from linear polarization to circular polarization, the onset position of laser filament formation becomes farther from the focusing optics, the filament length is shorter, and less laser energy is deposited. The laser polarization effect on air filaments is supported by a simulation and analysis of the polarization-dependent critical power and ionization rates in air.
320.2250 Femtosecond phenomena 260.5430 Polarization Chinese Optics Letters
2018, 16(7): 073201
Author Affiliations
Abstract
1 MOE Key Laboratory of Advanced Micro-structured Materials, Institute of Precision Optical Engineering, School of Physics Science and Engineering, Tongji University, Shanghai 200092, China
2 State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China
3 IFSA Collaborative Innovation Center, Shanghai Jiao Tong University, Shanghai 200240, China
4 Center for Optics, Photonics and Laser (COPL), Laval University, Quebec City, Quebec G1V 0A6, Canada
We report on the experimental observation of the airflow motion induced by an 800 nm, 1 kHz femtosecond filament in a cloud chamber filled with air and helium. It is found that vortex pairs with opposite rotation directions always form both below and above the filaments. We do not observe that the vortices clearly formed above the filament in air just because of the formation of smaller particles with weaker Mie scattering. Simulations of the airflow motion in helium are conducted by using the laser filament as a heat source, and the simulated pattern of vortices and airflow velocity agree well with the experimental results.
140.0140 Lasers and laser optics 190.0190 Nonlinear optics 320.0320 Ultrafast optics Chinese Optics Letters
2016, 14(3): 031401
加拿大拉瓦尔大学, 魁北克 GIVOA6, 加拿大
飞秒激光成丝现象已经开创了从纯物理到应用研究的许多新的科学研究领域,其中包括源于量子和经典物理的多个应用研究。飞秒光丝中的新现象,例如激光强度钳制效应、空气激光、粒子数捕获、分子排列、分子超激发态、光丝诱导降雪、光丝化学等等,开辟了令人振奋的、多学科交叉新领域。激光强度钳制效应是一个复杂的物理现象,结果可以形成一个非常稳定的相互作用状态。粒子数束缚、分子排列、转动及其周期性可被用于脉冲太赫兹辐射的远程探测。光丝中的空气激光现象看起来像是一种新的激发机制,例如,光丝中激光强度可以把氮气和二氧化碳分子激发到一种粒子数反转的状态。与此同时,这种光丝诱导激光现象(或粒子数反转)在空气中“污染分子”形成的分子碎片中也被观察到。利用单一激光,通过探测特征荧光来远程识别污染物、气体或者固体样品已经至少在原理上得到证实。光丝诱导沉积现象已经在云室中变成现实。最后讨论了光丝研究领域未来的挑战以及光丝化学为光丝研究提供的一个新的机遇。
激光成丝 四波混频 放大自发辐射 荧光辐射 filament four wave mixing amplified spontaneous emission fluorescence emission
Author Affiliations
Abstract
1 State Key Laboratory on Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, Changchun 130012, China
2 State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China
3 Centre d’Optique, Photonique et Laser et le Département de Physique, Université Laval, Quebec City, Quebec G1V0A6, Canada
The visible and near-UV emission spectroscopy of methane (CH4) induced by a femtosecond intense laser field (800 nm, 40 fs, 1014 W/cm2) is studied. By measuring the decay profiles of the neutral fragment product CH (A2Δ→X2Π), two reaction pathways, i.e., the electron-ion recombination through e +CH4+ and the direct disintegration of CH4+ are found to be responsible for populating the electronic excited states of the neutral fragment product CH, which gives rise to the photoemissions. Our results provide complementary information on previous understanding of the strong-field-induced photoemission mechanism of CH4 through neutral dissociation of superexcited states.
300.6410 Spectroscopy, multiphoton 300.2530 Fluorescence, laser-induced Chinese Optics Letters
2015, 13(7): 070007
Author Affiliations
Abstract
1 State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China
2 Key Laboratory of Opto-Electronic Information Science and Technology, Ministry of Education, Institute of Modern Optics, Nankai University, Tianjin 300071, China
3 Centre d'Optique, Photonique er Laser (COPL) and Dèpartement de Physique, de Gènie Physique et d'Optique, Universitè Laval, Quèbec, Quèbec G1K 7P4, Canada
With the evolution of a laser pulse in water, the formation of a nonlinear X wave during femtosecond filamentation is investigated based on numerical simulations. In particular, we analyze the far-field angularly resolved spectra obtained for different temporal portions of the ultrashort pulse during its propagation. Our result shows that the refocusing of ultrashort pulse leads to the formation of dynamic X wave which essentially manifests itself as conical emission.
飞秒成丝 脉冲传播 X波 320.0320 Ultrafast optics 190.5530 Pulse propagation and temporal solitons 070.4790 Spectrum analysis Chinese Optics Letters
2010, 8(2): 244
1 南开大学现代光学研究所教育部光电信息科学重点实验室, 天津 300071
2 拉瓦尔大学光学、光子学和激光中心,物理、工程物理和光学系,加拿大 魁北克 G1V 0A6
飞秒激光在空气中形成的等离子体细丝会辐射出太赫兹(THz)信号。实验利用1 mJ,800 nm, 50 fs的飞秒激光脉冲产生等离子体细丝。应用光电取样方法探测了激光成丝现象中前向辐射的THz脉冲,得到了持续时间为0.1 ps、光谱峰值在1 THz左右的单周期THz脉冲。转动抽运光的偏振态,分析了电光取样信号的变化。通过比较实验数据和计算结果,证明了成丝辐射THz脉冲的偏振态为椭圆偏振态。
非线性光学 超快光学 激光成丝 太赫兹波
1 南开大学现代光学研究所光电信息技术科学教育部重点实验室, 天津 300071
2 郑州大学河南省激光与光电信息技术重点实验室， 郑州 450052
3 加拿大拉瓦尔大学物理学、工程物理及光学系， 魁北克 加拿大 GIK7P4
大功率超快脉冲激光和气体相互作用可产生非线性荧光光谱，不同的气体分子具有不同的非线性荧光光谱，因而这种光谱可以作为物质的指纹模式加以识别分类，进而获知气体的成分。由于不同气体分子的光谱在同一波段上有很大的交叉重叠，用传统的光谱分析方法分析存在困难，采用神经网络方法分析上述非线性荧光光谱，利用经过预处理的荧光光谱数据作为模式样本，其中一部分样本作为学习样本对级联神经网络进行训练，用训练好的网络对所有样本进行实时识别，学习样本和测试样本的的正确识别率均可达100%，结果表明此方法可实时判断混合气体的组分。
光谱分析 模式识别 级联神经网络模型 非线性荧光光谱 指纹模式
