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Multi-pulsed intense electron beam emission from velvet,carbon fibers,carbon nano-tubes and dispenser cathodes
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XIA Lian-Sheng YANG An-Min CHEN Yi ZHANG Huang LIU Xing-Guang LI Jin JIANG Xiao-Guo ZHANG Kai-Zhi SHI Jin-Shui DENG Jian-Jun ZHANG Lin-Wen 《中国物理C(英文版)》2010,34(11):1733-1737
The experimental results of studies of four kinds of cathode emitting intense electron beams are demonstrated under multi-pulsed mode based on an experimental setup including two multi-pulse high voltage sources.The tested cathodes include velvet,carbon fibers,carbon nano-tubes(CNTs)and dispenser cathodes.The results indicate that all four are able to emit multi-pulsed beams.For velvet,carbon fiber and CNTs,the electron induced cathode plasma emission may be the main process and this means that there are differences in beam parameters from pulse to pulse.For dispenser cathodes tested in the experiment,although there is a little difference from pulse to pulse for some reason,thermal-electric field emission may be the main process. 相似文献
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This paper presents a Nd : YAG laser operating in free running (FR) regime, with a pulse duration (20 μs) shorter than conventional systems (>200 μs), mainly developed for applications in laser cleaning of stones, especially for the restoration of cultural heritage. The system was also optimized to achieve high energy and low divergence, for easy coupling with optical fibers. The unusual pulse temporal regime induces a spiky behavior of the laser output which could also help in the application. Details on the technologies for the flashlamps power supplies, including the discharge circuits needed to achieve the short pulses, are given. Application trials on artworks and artificial samples are also discussed. Results show that the intermediate pulse duration avoids the mechanical damage induced by the photomechanical effect of Q-switch lasers and the thermal damage, as superficial melting, usually induced by long pulse FR lasers. 相似文献
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《中国光学快报(英文版)》2017,(1)
We present a lamp-pumped Nd: phosphate glass laser amplifier delivering up to 1 J of pulse energy at 1053 nm with a repetition rate of 1 Hz and an injected pulse energy of 2.5 mJ. The amplifier system employs a beamshaping module and a four-pass, lamp-pumped amplifier. The thermally induced wavefront distortion is mitigated and a uniform gain distribution is obtained by a four-lamp-pumped laser head in the amplifier. Thus,an excellent beam quality is obtained. 相似文献
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Ultrashort Gaussian pulse-width expansion and shape deformation induced by group velocity dispersion
Pulse-width expansion and pulse-shape deformation of an ultrashort Gaussian pulse induced by both low and high order group
velocity dispersion were theoretically analyzed in terms of energy conservation and coupled equations for three wave radiations.
As an example, the optical parametric interaction processes in a negative uniaxial crystal of CsLiB6O10 with 50 fs of ultrashort Gaussian pulse were simulated. The results indicate that the degree of the pulse expansion induced
by low and high order group velocity dispersion is determined by both the wavelength of the incident wave and the crystal
length. A pulse could be expanded to 1.41 times its initial value as a crystal length equals the dispersion length and further
heavily expanded with decreasing wave-length and increasing crystal length. The pulse expansion induced by high order group
velocity dispersion using an incident wavelength of 213 nm is 1.6 times that when using 532 nm in a 50 fs pulse width without
chirp modulation, and the symmetry deformation and the frequency pushing phenomena of the ultrashort pulse shape are also
found.
The text was submitted by the authors in English. 相似文献
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Direct detection of ultrafast thermal transients by use of a chirped, supercontinuum white-light pulse 总被引:1,自引:0,他引:1
An experimental technique is demonstrated that permits direct optical measurement of ultrafast material transients during a single excitation-relaxation cycle. Reflection of a linearly chirped, supercontinuum optical pulse from a gold film with changing surface temperature induced by an ultrafast pump pulse allows the thermal transients to be encoded onto the spectrum of the probe pulse. Calibrating the chirp of the probe pulse and the wavelength sensitivity of the sample permits mapping of the measured transient into the time domain. Measurements are completed over the course of 100 ps with subpicosecond time resolution. Results obtained with this technique are compared with similar measurements obtained with conventional pump-probe correlation techniques. 相似文献
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《等离子体物理论文集》2017,57(1):29-39
In this paper, a two dimensional Particle In Cell‐Monte Carlo Collision simulation scheme is used to examine the THz generation via the interaction of high intensity ultra‐short laser pulses with an underdense molecular hydrogen plasma slab. The influences of plasma density, laser pulse duration and its intensity on the induced plasma current density and the subsequent effects on the generated THz signal characteristics are studied. It is observed that the induced current density in the plasma medium and THz spectral intensity are increased at the higher laser pulse intensities, laser pulse durations and plasma densities. Moreover, the generated THz electric field amplitude is reduced at the higher laser pulse durations. A wider frequency range for the generated THz signal is shown at the lower laser pulse durations and higher plasma densities. Additionally, it is found that the induced current density in hydrogen plasma medium is the dominant factor influencing the generation of THz pulse radiation. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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The excitation of a phase transient grating induced by two equal pulses from the same laser, which intersect in a nonlinear (cubic) medium, is considered theoretically. The grating parameters are calculated. The grating amplitude is shown to be spatially non-uniform and to be described by the pulse autocorrelation function, a display of the pulse coherence and of the two-pulse interference pattern. The diffraction problem of the induced grating is then solved using the electrodynamic perturbation theory. The diffraction efficiency of the grating is calculated. It is shown that the measurement of the spectral intensity of the probe light diffracted from the induced grating enables the complete computation of the grating amplitude. Such a measurement may be carried out for the whole of the time of grating decay after the excitation of the grating. Some possible applications of the induced grating are considered. The medium parameters and the autocorrelation trace of the single pulse may be determined. The shape and duration of a bandwidth-limited pulse or the spectrum of an arbitrary one are shown to be measurable. 相似文献
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Self-scattering of a transverse acoustic pulse from a longitudinal strain video pulse (induced by an acoustic pulse) in a paramagnetic crystal in a magnetic field is predicted. This effect is accompanied by a continuous frequency shift of the hypersonic pulse to the red region; this shift is proportional to the pulse intensity. 相似文献
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Z.-C. Luo A.-P. Luo W.-C. Xu J.-R. Liu H.-S. Yin 《Applied physics. B, Lasers and optics》2010,100(4):811-820
We report on the observation of the modulation instability induced by cross-phase modulation in a dual-wavelength operation
dispersion-managed soliton fiber ring laser with net negative cavity dispersion. The passively mode-locked operation is achieved
by using a nonlinear polarization rotation technique. A new type of dual-wavelength operation, where one is femtosecond pulse
and the other is picosecond pulse operation, is obtained by properly rotating the polarization controllers. When the dual-wavelength
pulses are simultaneously circulating in the laser ring cavity, a series of stable modulation sidebands appears in the picosecond
pulse spectrum at longer wavelength with lower peak power due to modulation instability induced by cross-phase modulation
between the two lasing wavelengths. Moreover, the intensities and wavelength shifts of the modulation sidebands can be tuned
by varying the power of the femtosecond pulse or the lasing central wavelengths of the dual-wavelength pulses. The theoretical
analysis of the modulation instability induced by cross-phase modulation in our fiber laser is also presented. 相似文献
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运用时域有限差分法计算了地面有限长电缆在高功率微波、超宽带和核电磁脉冲作用下的外导体感应电流。计算结果表明:场强相同情况下,核电磁脉冲在电缆上感应的电流最大,持续时间最长,高功率微波和超宽带在几m长和几十m长的电缆上感应的电流相差不大;入射角对电缆感应电流也有影响,电场方向与电缆平行时感应最强;地面电缆的感应电流振荡频率比自由空间中电缆的感应电流振荡频率低;随着大地电导率的增大,感应电流反射波衰减加快;电缆任一端接地后,接地端电缆感应电流都会增大。 相似文献
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研究了9.33 GHz高功率脉冲微波对IAR20鼠肝细胞和L-02人肝细胞增殖的影响,利用噻唑蓝比色法测量细胞增殖并对实验数据进行拟合,得到脉冲个数、场强和脉宽与细胞增殖之间的关系。当脉冲微波场强与脉宽保持不变,脉冲微波细胞效应随脉冲个数呈现非线性的指数递增规律。当脉冲微波的脉冲个数、脉宽一定时,场强越大,细胞增殖被抑制的程度越大;当脉冲个数、场强不变,脉宽越大,细胞增殖受到抑制的作用越明显,即脉冲微波细胞效应与场强和脉宽成正比。相同脉冲微波参量对不同种类细胞增殖的影响是不同的,对IAR20鼠肝细胞的影响比对L-02人肝细胞的影响略大。 相似文献
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应用激发态吸收增强瞬态热折射理论结合激发态折射理论研究了新型锌卟啉化合物Zn-porphyrin 中激发态吸收增强瞬态热折射与激发态折射间的相互竞争. 样品在不同脉宽激光激发下呈现自聚焦-自散焦间的转化. 当入射激光脉宽为4 ns时,激发态折射占主要地位,样品呈现自聚焦性质;当入射激光脉宽为8ns时,激发态吸收增强瞬态热折射占主要地位,激发态折射占次要地位,样品呈现自散焦性质.
关键词:
金属卟啉化合物
激发态折射
瞬态热折射 相似文献
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基于啁啾脉冲放大技术的超短脉冲激光系统是提供超快、超强激光的重要途径,具有良好输出波形和高损伤阈值的多层介质膜脉冲宽度压缩光栅是获得高峰值功率脉冲激光的关键. 基于傅里叶谱变换方法和严格模式理论,分析了多层介质膜光栅(MDG)在超短脉冲作用下的光学特性. 结果表明,当MDG的反射带宽小于具有高斯分布的入射脉冲的频谱宽度时,-1级反射脉冲呈非对称高斯分布,其前沿出现振荡,并且-1级反射脉冲能量开始剧烈下降. 讨论了MDG结构参数对其反射带宽的影响. 分析了MDG与超短脉冲作用时的近场光分布,对提高其抗激光损
关键词:
脉冲压缩光栅
傅里叶谱变换
模式理论
损伤阈值 相似文献