共查询到20条相似文献,搜索用时 15 毫秒
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利用“泵浦-探测”非共线双等离子体通道方法实现三次谐波增强。泵浦光与探测光间的耦合作用能有效改善探测光光丝中的饱和效应,克服光强钳制对谐波强度增加的限制。实验中将两束能量分别为4.4和10.2 mJ、中心波长均为810 nm、脉宽均为60 fs的超短脉冲在空气中非共线聚焦,能各自形成光丝且产生微弱三次谐波。当强光在时域上超前于弱光时,强光会预先成丝形成等离子体通道,对后续弱光产生调制,使探测光产生的三次谐波强度明显增强。实验发现270 nm谐波能量增加的显著区域内频谱宽度出现振荡变化,当两光以27.3 mrad小角度相交于几何焦点前约15 mm,且探测光滞后约55 fs时,获得的能量增长倍率达到近70倍,对应谱宽约为5 nm。 相似文献
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The propagation of picosecond deep ultraviolet laser pulse at wavelength of 193 nm in air is numerically investigated. Long plasma channel can be formed due to the competition between Kerr self-focusing and ionization induced defocusing. The plasma channel with electron density of above 10^13/cm^3 can be formed over 70 m by 50-ps, 20-mJ laser pulses. The fluctuation of laser intensity and electron density inside ultraviolet (UV) plasma channel is significantly lower UV laser by air is considered in the simulation and it the limit of the length of plasma channel. than that of infrared pulse. The linear absorption of is shown that the linear absorption is important for the limit of the length of plasma channel. 相似文献
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G. L. Chen H. Y. Lu C. Wang J. S. Liu R. X. Li G. Q. Ni Z. Z. Xu 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,47(2):303-307
We propose a plasma channel scheme to obtain an improved
table-top laser driven fusion neutron yield as a result of explosions of
large deuterium clusters irradiated by an intense laser pulse. A cylindrical
plasma channel is created by two moderate intensity laser prepulses at the
edge of a deuterium cluster jet along which an intense main laser pulse
propagates several nanoseconds later. With the aid of this plasma channel,
the main laser pulse will be allowed to deposit its energy into the central
region of the deuterium gas jet where the cluster sizes are larger and the
atomic density is higher. The plasma channel formation and its impact on the
deuterium ion energy spectrum and the consequent fusion neutron yield have
been investigated. The calculated results show that a remarkable increase of
the table-top laser driven fusion neutron yield would be expected. 相似文献
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We investigated the evolution of femtosecond laser pulses at different wavelengths corresponding to normal, zero, and anomalous regimes of group velocity dispersion (GVD) in fused silica. The laser pulse filamentation in different GVD regimes under the same similarity parameters was first considered. It was established numerically that the scenario of the pulse filamentation depends both on temporal factors, which are determined by pulse GVD and self-phase modulation, and spatial factors associated with Kerr self-focusing and plasma defocusing. In presence of strong normal GVD the dispersive stretching causes, a pulse power decrease followed by lowering of the intensity in filament, electron density reduction in plasma channel, and suppressing of the refocusing. For zero GVD the multipeak regime of radiation propagation is realized in the filament as a result of recurring self-focusings of powerful pulse tail, which was defocused in laser plasma. When GVD is anomalous a sequence of ??light bullets?? with duration about 10 fs forms in the filament. And the peak intensity in ??light bullet?? stays the same ?? 5 × 1013 W/cm2. In the regime of anomalous GVD power is transferred from the pulse edges to its center, where the repeated self-focusings occur and form a ??light bullet?? sequence. 相似文献
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A new physical effect of a plasma channel formation by the ponderomotive force of a wakefield generated by a laser pulse with a length of the order of the electron plasma wavelength is discussed. For a narrow pulse, wherein the width is less than c/omega(pe) ( omega(pe) and c are the plasma frequency and light velocity, respectively), the channel has an annular form with on-axis density maximum. The depth of the channel increases with the distance from the pulse until the phase mixing arises and the wake starts to break. The linear fluid theory is used to obtain the scaling for wave-breaking conditions. The results of numerical simulations for high intensity laser pulses are in good agreement with theoretical predictions. 相似文献
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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
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Takahashi K Kodama R Tanaka KA Hashimoto H Kato Y Mima K Weber FA Barbee TW Da Silva LB 《Physical review letters》2000,84(11):2405-2408
A laser self-focused channel formation into overdense plasmas was observed using a soft x-ray laser probe system with a grid image refractometry (GIR) technique. 1.053 &mgr;m laser light with a 100 ps pulse duration was focused onto a preformed plasma at an intensity of 2x10(17) W/cm (2). Cross sections of the channel were obtained which show a 30 &mgr;m diameter in overdense plasmas. The channel width in the overdense region was kept narrow as a result of self-focusing. Conically diverging density ridges were also observed along the channel, indicating a Mach cone created by a shock wave due to the supersonic propagation of the channel front. 相似文献
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Hidaka Y Choi EM Mastovsky I Shapiro MA Sirigiri JR Temkin RJ 《Physical review letters》2008,100(3):035003
We report the observation of two-dimensional plasma filamentary arrays with more than 100 elements generated during breakdown of air at atmospheric pressure by a focused Gaussian beam from a 1.5-MW, 110-GHz gyrotron operating in 3-micros pulses. Each element is a plasma filament elongated in the electric field direction and regularly spaced about one-quarter wavelength apart in the plane perpendicular to the electric field. The development of the array is explained as a result of diffraction of the beam around the filaments, leading to the sequential generation of high intensity spots, at which new filaments are created, about a quarter wavelength upstream from each existing filament. Electromagnetic wave simulations corroborate this explanation and show very good correlation to the observed pattern of filaments. 相似文献
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We investigate the filaments formed by the ultrashort laser pulses with different wavelengths of 400 nm, 586 nm and 800 nm propagating in argon. Numerical results show that, when the input power or the ratio of the input power to the critical power is given, the pulse with 400 nm wavelength has the largest on-axis intensity, as well as the narrowest filament and the most stable beam radius. These results indicate that the pulse with shorter wavelength is more suitable for the long-range propagation in argon. 相似文献
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N. S. Shahabuddin H. Mohamad M. A. Mahdi Z. Yusoff H. Ahmad S. W. Harun 《Laser Physics》2012,22(1):212-215
A simple multi-wavelength source is demonstrated based on spectral slicing of supercontinuum (SC) light using a Sagnac loop
mirror. A mode locked fiber laser with pulse width of 800 fs is employed to generate the SC in photonic crystal fiber (PCF).
The SC light extending from 1200 nm up to the wavelength region above 1750 nm is obtained at the amplified pulse pump power
of 30 dBm. By slicing the SC with a loop mirror, a multiwavelength comb spectrum is obtained with different channel spacing
for different operating wavelength region. Spacings of 1.5, 2.3, and 2.9 nm are shown at wavelength regions of 1220, 1450,
and 1730 nm, respectively. It is also observed that the signal to noise ratio (SNR) increases from 15 to 20 dB as the operating
wavelength increases from 1220 to 1730 nm region. 相似文献
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Competition between multiphoton/tunnel ionization and filamentation induced by powerful femtosecond laser pulses in air 总被引:1,自引:0,他引:1
In this work we present experiments by focusing 42 femtosecond laser pulses in air using three differentfocal length lenses: f=100, 30 and 5 cm. For the longest focal length, only the filament, which is aweak plasma column,is observed. When the shorter focal length lens is used, a high density plasma isgenerated near the geometrical focus and coexists with a weak plasma channel of the filamemt. Under thetightest focusing condition, filamentation is prevented and only a strong plasma volume appears at tehgeometrical focus. 相似文献
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Janulewicz KA Schnürer M Tümmler J Priebe G Risse E Nickles PV Greenberg B Levin M Pukhov A Mandelbaum P Zigler A 《Optics letters》2005,30(12):1572-1574
Investigations of plasma produced by a boron nitride capillary discharge irradiated with a guided 20-TW Ti: sapphire laser pulse at a peak intensity of 4 x 10(18) W/cm2 are presented. The guided laser radiation in the plasma channel generated He-like ions that, subject to suitable plasma temperature, recombined into Li-like nitrogen ions. Intense radiation at a wavelength of 24.77 nm was observed, indicating possible lasing at the 3d(5/2) - 2p(3/2) transition in Li-like nitrogen. 相似文献
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采用热丝化学气相沉积(chemical vapor deposition,CVD)的方法,以丙酮为碳源生长金刚石薄膜时,利用等离子体发射光谱对生长过程中的等离子体空间分布进行了在线诊断。采用SEM,Raman光谱分别对沉积金刚石膜表面、断面的形貌和质量进行表征。光谱分析表明,对于线性阵列布丝情况下,中心区域与边缘区域的基团分布存在差异,中心区温度高,裂解能力强,基团强度高于两边,但中心区域基团特征峰强度的变化比等离子球平缓的多;距离热丝越远,热辐射减小,从丙酮分子中裂解出CH和CO等基团以及由原子H激发的Hβ与Hα等强度降低,反而使得复合生成的C2基团增加。SEM测试结果表明,当丝基间距为4.5,5.5,6.5 mm时,所沉积的金刚石薄膜表面由致密规则晶面向混乱转变,且单位时间内的生长速率也依次降低,此外,Raman光谱表明随着纵向间距的加大,金刚石薄膜的质量随之降低。这与诊断结果中CH和CO强度的降低,C2基团强度增加及基团C2/Hα比强度下降相吻合。 相似文献
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基于大气湍流效应的双波长激光传输特性实验研究 总被引:1,自引:0,他引:1
为研究大气湍流作用下不同波长激光信号的传输特性,建立了基于双波长条件下的激光光束传输实验测试系统,在此基础上进行了室外实验测量,得到了双波长光束同信道传输时的光束漂移和光强起伏变化的测试数据。实验结果表明,大气湍流对激光信号的传输具有较大的影响,且光强的闪烁系数与波长有很大的关系,选择波长较长的激光束可减少湍流对光强起伏的影响;光束质心漂移具有很大的随机性,且其质心变化与波长之间无明显的直接联系。实验测试数据结果与大气湍流理论相符合,对空间大气通信具有一定的参考价值。 相似文献
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利用三维经典系综模型,研究了整个系综两电子(Ar原子为例)从激光场吸收的能量对激光参数(波长、激光强度和椭偏率)的依赖关系.结果显示,当激光强度固定,波长增加时,整个系综两电子从激光场吸收的能量整体呈上升趋势,但不同强度下趋势略有差异.在较低强度时整个系综两电子从激光场吸收的能量对波长的依赖关系呈现持续平稳增加的趋势,在较高强度时呈现先缓慢减小再快速增大的趋势.对强度的依赖关系在不同波长时呈现两个有趣的交叉点.对椭偏率的依赖关系在较低强度时呈现先逐渐减小再缓慢增大的趋势;在中等强度时呈现一个“阶梯型”即先缓慢增大再逐渐减小最后缓慢增大;在更高强度时呈现先逐渐增大再逐渐减小的趋势.为了解释整个系综两电子从激光场吸收的能量对激光参数的依赖关系,把整个系综的动力学过程分为双电离、单电离、受挫单电离和受挫双电离4种通道.然后分析各个通道的特征及其如何主导整个系综两电子从激光场吸收的能量的变化趋势.分析结果表明,整个系综两电子从激光场吸收的能量对波长、激光强度和椭偏率的依赖均是由于某种通道主导整个系综两电子从激光场吸收的能量的结果. 相似文献
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The absorption spectra, fluorescence spectra, and lifetimes of as-grown and annealed Cr,Yb:YAG crystal grown by Czochralski technique have been measured. The broad absorption bands in the visible region increase in intensity and shift to long wavelength after annealing, and the additional absorption around 482 nm may be possibly due to new octahedral Cr4+ center in the crystal, and the increase in the infrared (IR) region is due to the increase of Cra+. The increase of Cr4+ also results in the groud state absorption and the concentration quenching of Ybs+ in Cr,Yb:YAG crystal after annealing, the fluorescence intensity is reduced to 75% and the emission lifetime is shortened from 1.40 to 0.44 ms. 相似文献