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1.
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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本文基于飞秒激光等离子体丝诱导击穿光谱对土壤重金属Cr元素含量进行了实验研究.利用荧光法对等离子体丝的长度进行测量,给出了在不同焦距聚焦透镜作用下土壤中Cr425.5 nm的谱线强度空间分布,实验给出了Cr元素的定标曲线.实验结果表明,土壤中Cr元素浓度分析测量的相对标准偏差小于5%,土壤中重金属Cr元素的检测极限为7.85 ppm.表明飞秒激光等离子体丝诱导击穿光谱技术在土壤重金属Cr元素含量的定量探测方面是完全可行的. 相似文献
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Suk Zhao B Sung Chung H Cho K Hyup Lee S Hwang S Yu J Ahn YH Sohn JY Kim DS Kyung Kang W Chung DS 《Physical review letters》2000,85(13):2705-2708
A cylindrical molecular lens is formed by focusing a nanosecond IR laser pulse. Trajectories of a CS2 molecular beam deflected by the lens are traced using the velocity map imaging technique. The characteristic lens parameters including the focal length, minimum beam width, and distance to the minimum-width position are determined. The laser intensity dependence of the parameters is in good agreement with theoretical predictions. Exciting possibilities for molecular optics and a new type of optical chromatography are opened up. 相似文献
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An 800-MHz self-mode-locked femtosecond Ti:sapphire laser has been developed whose mode-lock frequency can be robustly scanned and modulated. The laser is based on the three-element design of Ramaswamy-Paye and Fujimoto [Opt. Lett. 19, 1756 (1994)]. By translation and modulation of the position of the prismatic output coupler, the mode-lock frequency can be reliably scanned more than 1% and modulated at 80 Hz with a deviation of 2.5 kHz without interrupting the mode lock, changing the pulse length, or inducing significant amplitude modulation. An application in tunable high-resolution terahertz spectroscopy is also demonstrated. 相似文献
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Jung-Kyu Park Ji-Wook Yoon Kyung-Hyun Whang Sung-Hak Cho 《Applied Physics A: Materials Science & Processing》2012,108(2):269-274
The effective removal of nanoparticles from a silicon wafer surface was demonstrated using the self-channeled plasma filament excited by a femtosecond (130?fs) Ti:sapphire laser (?? p=790?nm). The photoinduced self-channeled plasma filament in air reached a length of approximately 110?C130?mm from the first focal spot with diameters ranging from 40 to 50???m at input intensities of more than 1.0×1014?W/cm2. By the scan of wafer using the X?CY?CZ stage during self-channeled plasma filament, the removal variation of nanoparticles on surface was observed in situ before and after the plasma filament occurred. The cleaning efficiency was strongly dependent on the gap distance between the plasma filament and the surface. The removal efficiency of nanoparticles reached 96?% with no damage to the surface when the gap was 150???m. 相似文献
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Generation of terahertz surface polaritons in homogeneous round cross-section plasma waveguides upon nonlinear optical rectification of femtosecond laser pulses is analyzed theoretically. It is assumed that nonlinear polarization inducing a surface electromagnetic wave is formed at the waveguide boundary in a thin layer of the nonlinear dielectric that surrounds the waveguide. The efficiency of the femtosecond radiation conversion into surface polaritons is studied as a function of the waveguide radius and duration of the exciting laser pulse. 相似文献
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A. El Fatimy J.C. Delagnes E. Nguema W. Knap P. Mounaix 《Optics Communications》2009,282(15):3055-3058
The possibility of using plasma wave field effect transistor in a time domain terahertz (THz) spectroscopy setup is presented. We demonstrate that High Electron Mobility Transistors (HEMTs) is an efficient device for detection of pulsed terahertz electric fields generated with a femtosecond laser oscillator. The response was observed in the frequency range of about 1 THz, far above the cutoff frequency of the transistors at room temperature. We show that the physical mechanism of the detection is related to the plasma waves excited in the transistor channel and that significant improvement of the active device can be achieved by increasing the drain current. The two-dimensional terahertz imaging applications clearly demonstrate that plasma wave nanometer HEMT should be employed as efficient future detectors in a matrix configuration. 相似文献
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利用皮秒和飞秒激光研究了激光在空气中聚焦产生单个等离子体通道的条件.研究发现,能量为8—12mJ皮秒激光被焦距为15cm的透镜聚焦后,可以产生较为稳定的单个通道.通过横向纵向阴影成像分析发现,通道的管壁对聚焦产生的自发光具有箍缩作用,而通道内部却有利于光的传输.同时还发现,当采用短焦距透镜时,能量低于10mJ的飞秒激光在空气中较易形成单个等离子通道.
关键词:
等离子体通道
皮秒激光
飞秒激光
阴影成像 相似文献
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The onset and recurrence of multiple filamentary structures in the long-distance propagation of high power femtosecond laser pulses in air displays features analogous to strong turbulence events observed in many areas of physics. However, dissipation is not a key player in regularizing the underlying singular dynamical events. The collapse singularity of the two-dimensional (2D) nonlinear Schrodinger equation is identified as the robust nonlinear mode which both initiates and sustains the waveguide. Physical collapse regularization mechanisms include normal group velocity dispersion and plasma generation in the high intensity nonlinear focal regions. Plasma absorption is weak and the dominant process is the transient generation of a highly localized strongly defocusing lens which evacuates the light behind the leading intense light filament. Consequently the nonlinear waveguide formed is highly dynamic. (c) 2000 American Institute of Physics. 相似文献
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The results of a theoretical analysis of the generation of broadband radiation in the infrared and terahertz spectral ranges
upon the excitation of plasma in air by two femtosecond pulses at the fundamental and second-harmonic frequencies of a Ti-sapphire
laser are presented. It is found that the appearance of long-wavelength radiation in a strong field of pulses of different
frequencies can be described in terms of strongly anharmonic oscillations of optical electrons, whereby electrons are pulled
far away from their atoms; these oscillations are accompanied by cascade transitions of electrons from their ground state
to a bound excited state, followed by a transition to the continuum. It is shown that the generated infrared and terahertz
radiation appears in the form of pulses containing a few oscillations of the light field. The efficiency of terahertz generation
varies periodically with an increase in the interaction length of the femtosecond pulses of different frequencies. 相似文献
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R. A. Akhmedzhanov I. E. Ilyakov V. A. Mironov E. V. Suvorov D. A. Fadeev B. V. Shishkin 《JETP Letters》2009,88(9):569-573
Experimental results on the generation of terahertz radiation in the gas breakdown by high-power quasi-monochromatic laser pulses focused by an axicon lens are presented. A theoretical model developed for the terahertzradiation generation includes the nonlinear interaction of a femtosecond pulse with an ionized gas and the excitation of transverse oscillations of the plasma column. The results of the theoretical analysis are compared with the experimental data. 相似文献
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The multiple filamentation of terawatt femtosecond(fs) laser pulses is experimentally studied in a natural environment.A more than 30-m long plasma filament with a millimeter diameter is formed by the collimated fs laser pulse freely propagating in an open atmosphere. This study provides the first quantitative experimental data about the electron density of a long range light filament in the atmosphere. The electron density of such a filament is quantitatively detected by using an electric method, showing that it is at the 10~(11)-cm~(-3) level. 相似文献
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N. A. Panov O. G. Kosareva V. A. Andreeva A. B. Savel’ev D. S. Uryupina R. V. Volkov V. A. Makarov A. P. Shkurinov 《JETP Letters》2011,93(11):638-641
A phenomenological model of the terahertz radiation of the plasma channel of a femtosecond filament has been elaborated that
satisfactorily describes the experimental results of the detection of low-frequency radiation in air. The angular distributions
of the terahertz radiation intensity in the absence and presence of an external electrostatic field have been obtained. The
dependence of the divergence angle of the terahertz radiation on the filament parameters has been determined. 相似文献
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M. I. Bakunov R. V. Mikhaylovskiy M. Tani C. T. Que 《Applied physics. B, Lasers and optics》2010,100(4):695-698
A structure that can provide enhancement of terahertz emission from a semiconductor surface excited with femtosecond laser
pulses is proposed. The structure consists of a semiconductor layer on a Si substrate with metal coating on the upper surface
of the layer and a Si lens attached to the bottom of the substrate. The semiconductor is excited through a hole in the coating
and emits terahertz radiation through the substrate lens. We demonstrate theoretically that the proposed structure can increase
the terahertz yield by orders of magnitude as compared to the previously used schemes of terahertz emission from a semiconductor
surface. 相似文献
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K. Jakubczak T. Mocek B. Rus J. Polan J. Hrebicek M. Sawicka P. Sikocinski J. Sobota T. Fort L. Pina 《Opto-Electronics Review》2011,19(2):169-175
We present results on development and experimental implementation of a 1-kHz, coherent extreme ultraviolet (XUV) radia- tion
source based on high-order harmonic generation of the femtosecond, near-infrared laser pulses produced by the titanium-doped
sapphire laser system (35 fs, 1.2 mJ, 810 nm) at the Institute of Physics AS CR / PALS Centre. The source comprises a low-density
static gas cell filled with a conversion medium, typically argon. The comprehensive optimization of the XUV harmonic source
has been performed with respect to major parameters such as gas pressure in the cell, cell length, position of the focus of
the driving laser field with respect to the gas cell position, size of the driving near-infrared laser beam, chirp of the
femtosecond pulse, and the focal length of the lens deployed in the experimental setup. Harmonic spectra were recorded using
an XUV transmission grating spectrometer developed specifically for this purpose. Detailed characterization of the XUV source
has been performed including measurement of the XUV beam profile, M2 parameter of the beam, absolute energy, and spatial coherence. 相似文献
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Based on natural protein materials, a series of lenses with different heights and focal lengths were assembled on glass substrates by femtosecond laser non-contact, masking, and cold processing. This lens array itself possesses unique and characteristic optical performance in three-dimensional parallel imaging and bending imaging. What is more profound is that by using equilibrium swelling of protein-hydrogel, once the lens array was placed in a liquid environment, with the change of ion concentration(e.g., pH), the refractive index and curvature of the protein-hydrogel would change, which leads to the flex of the focal plane of the lens, finally realizing the dynamical tunability of a protein microlens. These smart stress devices may have great potential in optical biosensing and microfluidic chip integration fields. 相似文献