共查询到20条相似文献,搜索用时 935 毫秒
1.
Q. Luo S.A. Hosseini W. Liu J.-F. Gravel O.G. Kosareva N.A. Panov N. Aközbek V.P. Kandidov G. Roy S.L. Chin 《Applied physics. B, Lasers and optics》2005,80(1):35-38
This paper describes the effects observed during the propagation of intense femtosecond laser pulses in air following the modification of the laser beam diameter with a pair of convex–concave lenses placed/mounted in a telescopic configuration. We observed that by reducing the diameter of the beam the detected back-scattered nitrogen fluorescence from the filaments becomes more stable on a shot-to-shot basis while, for a larger beam size, greater fluctuations are observed that are not correlated to shot-to-shot fluctuations in the laser pulse energy. This result leads to a new method to control the fluorescence signal which can be very important in remote-sensing applications. PACS 42.65.Jx; 42.68.Ay; 42.68.Wt 相似文献
2.
Effective length of filaments measurement using backscattered fluorescence from nitrogen molecules 总被引:2,自引:0,他引:2
S.A. Hosseini Q. Luo B. Ferland W. Liu N. Aközbek G. Roy S.L. Chin 《Applied physics. B, Lasers and optics》2003,77(6-7):697-702
The effective length of self-induced long (100 meters) plasma filaments, generated by intense femtosecond near IR laser pulses in air, was measured remotely using a lidar technique. This technique is based on detecting the backscattered fluorescence signal from nitrogen molecules excited along the intense laser pulse propagation path. This opens up the possibility of measuring remotely long filaments extending over hundreds of meters in the atmosphere. PACS 42.65.Jx; 42.68.Ay; 42.68.Wt 相似文献
3.
J.-F. Daigle O. Kosareva N. Panov M. Bégin F. Lessard C. Marceau Y. Kamali G. Roy V. P. Kandidov S. L. Chin 《Applied physics. B, Lasers and optics》2009,94(2):249-257
A simple method to produce longer filaments with higher ionization density in air by controlling the diameter of an aperture
in the laser beam path is studied via an analysis of the backscattered N2 fluorescence collected by LIDAR. Significant increase in the fluorescence signal (approximately by a factor of five depending
on the conditions) and an increased filament length was observed at an optimum diameter. 3D + time stochastic numerical simulations
have shown that the optimum aperture size corresponds to the case of multiple filament ‘squeezing’ around the propagation
axis forming the regularized elongated structure with higher overall amount of plasma. The optimum range of aperture sizes
is the same for the initial transverse perturbation scale variation at least within a factor of three. 相似文献
4.
5.
The longitudinal plasma profile of a laboratory scale filament induced by the propagation of an intense femtosecond laser pulse in air was measured simultaneously by three different methods. Each of them is based on a specific property of the filament, including electromagnetic pulse emission, backward emitted nitrogen fluorescence, and acoustic wave generation. Although each of above methods has been separately reported, it is the first time that a simultaneous multi-parameter measurement on a laser filament is presented. Such multiparameter measurement allows a direct comparison between the different methods, and a better understating of the dynamics of a filament from its generation through multi-photon/tunnel ionization (MPI/TI) to its damping through acoustic wave emission. The advantages as well as drawbacks of each method are analyzed in a comparative way. PACS 42.65.Jx; 42.68.Ay; 42.68.Wt 相似文献
6.
The triggering and guiding of high voltage discharge by plasma filaments generated by 400 nm and 800 nm femtosecond laser were studied experimentally. The detailed diagnostics for characteristics of filaments, such as amount of free electrons, diameter and electron density, were performed using sonographic method, fluorescence imaging and resistivity measurement. A significant reduction of the breakdown voltage threshold due to the pre-ionization of the air gap by laser pulse filaments was observed. It is shown that the 400 nm laser pulses demonstrated stronger triggering ability than 800 nm laser pulse under same pulse energy. This behavior of 400 nm femtosecond pulse is connected to the rich population of highly excited particles in filaments. 相似文献
7.
为精确再现超强飞秒脉冲激光在大气中的传输特性,有效控制激光诱导等离子体通道的性能参数,基于扩展的非线性薛定谔方程,研究了空气中产生的等离子通道的演变过程。该模型在考虑衍射、色散和多光子效应的基础上,引入了拉曼散射、等离子体尾波场和相对论自聚焦等多种效应。讨论了电子密度和光强通量的空间分布特性,运用分步傅里叶法和有限差分法得到了电子密度和光强通量的分布,仿真结果显示,激光波长、单脉冲能量、脉宽和束腰半径等初始参数的变化将对等离子体通道的演变产生显著影响,为超短脉冲强激光在大气中成丝位置和形态控制提供了可能的途径。 相似文献
8.
A. A. Ionin S. I. Kudryashov S. V. Makarov L. V. Seleznev D. V. Sinitsyn 《JETP Letters》2009,90(6):423-427
The propagation of focused femtosecond laser pulses with supercritical peak powers in air has been investigated by the methods
of optical visualization, profilometry, and calorimetry. Laser pulses with supercritical powers create a bundle of submillimeter
filaments with a diameter of about 5 μm ahead of the lens focus; the maximum number of filaments in the beam cross section
and their length increase linearly and sublinearly, respectively, with the radiation peak power. The optical visualization
and calorimetry indicate that the plasma channels of filaments are optical contrast (a plasma density of 1018–1019 cm−3), ensuring the refraction of laser radiation incident on them. 相似文献
9.
W. Liu F. Théberge J.-F. Daigle P.T. Simard S.M. Sarifi Y. Kamali H.L. Xu S.L. Chin 《Applied physics. B, Lasers and optics》2006,85(1):55-58
The unavoidable hot spots in a practical terawatt level laser pulse will self-focus in air at a short distance. The short distance cannot be changed significantly by only controlling the chirp or divergence. We overcome such early self-focusing by using a telescope, which enlarges the diameter of the beam, thus that of the hot spots. The telescope’s effective focal length is much shorter than the self-focusing distance of both the enlarged beam and the hot spots. Then, the resulting filaments merge into the geometrical focus whose position is controllable by the telescope. This technique also minimizes the generation of white light. PACS 52.38.Hb; 42.65.Jx; 52.35.Mw 相似文献
10.
Triggering and guiding of high voltage discharge by using femtosecond laser filaments with different parameters 下载免费PDF全文
This paper demonstrates the triggering and guiding of the stationary
high voltage (HV) discharges at 5--40 kV by using plasma filaments
generated by femtosecond laser pulses in air. A significant
reduction of the breakdown voltage threshold due to the
pre-ionization of the air gap by laser filamentation is observed.
The discharge experiments are performed by using laser pulses with
different energy from 15--60 mJ. The electron density of filaments
is detected by sonography method. The influence of the electron
density of laser filaments on the triggering and guiding HV
discharge is experimentally investigated. The results have shown
that the behaviour of plasma filaments can strongly affect the
efficiency of triggering and guiding HV discharge. 相似文献
11.
Deng YP Zhu JB Ji ZG Liu JS Shuai B Li RX Xu ZZ Théberge F Chin SL 《Optics letters》2006,31(4):546-548
We investigate the evolution of filamentation in air by using a longitudinal diffraction method and a plasma fluorescence imaging technique. The diameter of a single filament in which the intensity is clamped increases as the energy of the pump light pulse increases, until multiple filaments appear. 相似文献
12.
D. A. Jones E. L. Kane P. Lalousis P. R. Wiles H. Hora 《Applied physics. B, Lasers and optics》1982,27(3):157-159
We describe the results of a numerical code which models the relativistic selffocussing of high-intensity laser beams in plasmas by the nonlinear relativistic dependence of the optical constants on laser intensity. The plasma dynamics of 1013 W Nd glass lasers of 30 m initial beam diameter in nearly cut-off density plasmas is followed for a few picoseconds interaction time and 25 m depth into the plasma. Rapid relativistic selffocussing down to a beam diameter of one micron in a distance of the order of the original beam diameter is observed, as well as the production of GeV ions moving against the laser light. 相似文献
13.
Femtosecond laser filamentation is particularly interesting for remote sensing pollutant in the atmosphere. In this work, we investigate the local shot-to-shot stability of the filament induced fluorescence of nitrogen in air. It is found that the root-mean square fluctuation of the fluorescence signal is at least one order of magnitude lower than that of the linear propagation case. In practice, it would contribute to improve the robustness of long distance spectroscopic analysis of the fluorescence of pollutant molecules inside the filament. We further point out that this unique property of filament induced fluorescence spectroscopy is because of the intensity clamping, a profound phenomenon of filamentation. 相似文献
14.
Naveen Gupta 《等离子体物理论文集》2019,59(2):154-165
This paper presents a theoretical investigation of the propagation characteristics of a q‐Gaussian laser beam propagating through a plasma channel created by the ignitor‐heater technique. The ignitor beam creates the plasma by tunnel‐ionization of air. The heater beam heats the plasma electrons and establishes a parabolic channel. The third beam (q‐Gaussian beam) is guided in the plasma channel under the combined effects of density non‐uniformity and non‐uniform ohmic heating of the plasma channel. Numerical solutions of the non‐linear Schrodinger wave equation (NSWE) for the fields of laser beams are obtained with the help of the moment theory approach. Particular emphasis is placed on the dynamical variations of the spot size of the laser beams and the longitudinal phase shift of the guided beam with the distance of propagation. 相似文献
15.
M. Hanif M. Salik Nek M. Sheikh M. A. Baig 《Applied physics. B, Lasers and optics》2013,110(4):563-571
We present the optical emission characteristics of the barium plasma produced at the surface of barium hydroxide Ba(OH)2, also known as baryta, generated by the first harmonic (1,064 nm) of a Q-switched Nd:YAG laser. The laser beam was focused on target material by placing it in air at atmospheric pressure. The experimentally observed line profiles of neutral barium have been used to extract the electron temperature using the Boltzmann plot method, whereas the electron number density has been determined from the Stark broadening. The electron temperature is calculated by varying distance from the target surface along the line of propagation of plasma plume and also by varying the laser energy. Besides, we have studied the variation of number density as a function of laser energy as well as its variation with distance from the target surface. It is observed that electron temperature and electron number density increase as laser energy increases. 相似文献
16.
G. Méjean J. Kasparian J. Yu S. Frey E. Salmon R. Ackermann J.P. Wolf L. Bergé S. Skupin 《Applied physics. B, Lasers and optics》2006,82(3):341-345
We report new experimental and numerical results on supercontinuum generation at ultraviolet/visible wavelengths produced
by the propagation of infrared femtosecond laser pulses in air. Spectral broadening is shown to similarly affect single filaments
over laboratory distance scales, as well as broad beams over long-range propagation distances. Numerical simulations display
evidence of the crucial role of third harmonic generation in the build-up of UV–visible wavelengths, by comparison with current
single-envelope models including chromatic dispersion and self-steepening.
PACS 52.38.Hb; 42.65.Tg; 42.65.Jx; 42.68.Ay 相似文献
17.
The generation of extremely stable light bullets in a preformed plasma near critical density has been observed experimentally during the interaction of intense picosecond laser beam with a metallic target in air. Optical probing measurements indicate the formation of pulsating channels, typically of about 5 microm in diameter, directed towards a heating laser beam, as well as of disconnected massive plasma blocks moving also towards the laser beam. The velocities of the dense plasma blocks reach the values of 4.5x10(8) cm/s. The blocks are stable during their acceleration and propagation in air. Self-generated magnetic fields up to 4-7 MG were observed by means of the Faraday rotation of a probe laser beam. 相似文献
18.
V. D. Zvorykin A. O. Levchenko A. G. Molchanov I. V. Smetanin N. N. Ustinovskii 《Bulletin of the Lebedev Physics Institute》2010,37(2):60-64
The grazing mode of microwave propagation in a hollow plasma waveguide formed by ionization of atmospheric air with a small
easily ionized additive by strong UV pulses of the Garpun KrF laser (λ = 248 nm, the pulse duration and energy are ∼70 ns and ∼50 J) was experimentally demonstrated for the first time. The annular
laser beam produced a hollow tube ∼10 cm in diameter with an electron density of ∼1012 cm−3 in a plasma wall ∼1 cm thick, over whichmicrowave radiation with λ
mw
∼ 8 mm was transmitted to a distance of 60 m. Themicrowave signal transmitted by the waveguide was amplified by a factor
of 6 in comparison with propagation in free space. 相似文献
19.
基于等离子体荧光法研究了Nd∶YAG纳秒1 064 nm激光脉冲诱导击穿空气等离子体的膨胀动力学过程,用ICCD相机捕获了不同激光脉冲能量诱导的空气等离子体随时间演化图像,给出激光能量100,150,200,300 mJ时击穿空气产生的空气等离子体波阵面前沿的膨胀距离,推演出空气等离子体的扩展速度。实验结果表明等离子体发光区域主要分布在等离子体膨胀区域,等离子体荧光强度随时间增加变强然后渐渐变弱,膨胀区域逐渐增大,在300 mJ,22 ns膨胀距离最大达到3.76 mm,等离子体扩展速度在膨胀初期达到105 m·s-1量级,在膨胀16 ns内迅速衰减,随后趋于平缓。激光脉冲能量越大,引起空气击穿的时刻靠近高斯激光脉冲上升阶段。 相似文献
20.
We present the optical emission studies of sulphur (S) plasma generated by the first (1064 nm) and second (532 nm) wavelengths of a Q-switched Nd:YAG laser. The target material was placed in front of laser beam in air at atmospheric pressure. The experimentally observed line profiles of neutral sulphur have been used to extract the electron temperature (T e ) using the Boltzmann plot method, whereas the electron number density (N e ) has been determined from the Stark broadening. The electron temperature is calculated by varying, distance from, the target surface along the line of propagation of plasma plume and also by varying the laser irradiance. Beside we have studied the variation of number density as a function of laser irradiance as well as its variation with distance from the target surface. It is observed that electron temperature and electron number density increases as laser irradiance is increased. 相似文献