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ABSTRACT: We present the spectral dynamics investigations of supercontinuum generation from 2.6TW femtosecond laser pulses propagation
in air. The measured spectra in the supercontinuum channel show a large amount of oscillating structure, which is mostly contributed
from four-wave mixing, stimulated Raman scattering and the electronic mechanism self-phase modulation. The temporal coherence
length is almost the same as 0.45ps for each spectral component with the same spectral width of supercontinuum that is confirmed
with a Michelson interferometer. The spatial coherence property of supercontinuum is measured by a Young’s double slit diffractometer,
which demonstrates that supercontinuum preserves a transverse coherence of about 144μm because of the divergence of the supercontinuum
channel.
Applied Physics B 04/2012; 92(2):153-157. · 2.19 Impact Factor
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Z Jin,
Z L Chen,
H B Zhuo,
A Kon,
M Nakatsutsumi,
H B Wang,
B H Zhang,
Y Q Gu,
Y C Wu,
B Zhu,
L Wang,
M Y Yu,
Z M Sheng,
R Kodama
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ABSTRACT: Near-infrared radiation around 1000 nm generated from the interaction of a high-density MeV electron beam, obtained by impinging an intense ultrashort laser pulse on a solid target, with a metal grating is observed experimentally. Theoretical modeling and particle-in-cell simulation suggest that the radiation is caused by the Smith-Purcell mechanism. The results here indicate that tunable terahertz radiation with tens GV/m field strength can be achieved by using appropriate grating parameters.
Physical Review Letters 12/2011; 107(26):265003. · 7.37 Impact Factor
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ABSTRACT: We developed for the first time, very compact (<1 cm3) extremely low f-number (f/# = 0.4) confocal ellipsoid focusing systems. Direct measurement of the laser focal spot using a low-energy laser beam indicates 1/5 reduction of the spot size compared to standard focusing (using a f/2.7 optics). Such mirror is thus able to achieve significant enhancement of the focused laser intensity without modifying the laser system itself. The mirror is then used under plasma mirror regime which enables us to compactify the size, to liberate us from the anxiety of protecting the optics from target debris after shots, and to enhance the temporal contrast. In this paper, we focus our attention to designing and optimizing the geometry of such innovative plasma optics.
Journal of Physics Conference Series 09/2010; 244(3):032008.
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ABSTRACT: It is found that stable proton acceleration from a thin foil irradiated by a linearly polarized ultraintense laser can be realized for appropriate foil thickness and laser intensity. A dual-peaked electrostatic field, originating from the oscillating and nonoscillating components of the laser ponderomotive force, is formed around the foil surfaces. This field combines radiation-pressure acceleration and target normal sheath acceleration to produce a single quasimonoenergetic ion bunch. A criterion for this mechanism to be operative is obtained and verified by two-dimensional particle-in-cell simulation. At a laser intensity of ∼5.5×10(22) W/cm(2), quasimonoenergetic GeV proton bunches are obtained with ∼100 MeV energy spread, less than 4° spatial divergence, and ∼50% energy conversion efficiency from the laser.
Physical Review Letters 08/2010; 105(6):065003. · 7.37 Impact Factor
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ABSTRACT: We present an estimation of Smith-Purcell Radiation by electrons generated in laser-plasmas interaction, passing near a metallic grating surface. The radiation wavelengths change with different grating periods and emission angles. The output photon numbers are also estimated. This effect could be developed into a new kind of tuneable table-top radiation source and also a diagnostics for the electron transport in over-dense plasmas.
Journal of Physics Conference Series 06/2008; 112(2):022087.
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ABSTRACT: The authors have proposed introducing a micro pulse power technology in high power laser plasma experiments to boost up the return current, resulting in efficiently guiding of energetic electrons. High current pulse power generators with a pulse laser trigger system generate high-density plasma that is well conductor. To efficiently guiding by using a micro pulse power, we estimated parameter of a micro pulse power system that is voltage of rise time, current, charging voltage and capacitance.
Journal of Physics Conference Series 06/2008; 112(2):022109.
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ABSTRACT: Rich soft X-ray emission lines of highly charged silicon ions (Si VI--Si XII) were observed by irradiating an ultra-intense laser pulse with width of 200 fs and energy of $\sim$90 mJ on the solid silicon target. The high resolution spectra of highly charged silicon ions with full-width at half maximum (FWHM) of $\sim$0.3--0.4\AA is analyzed in wavelength range of 40--90 \AA . The wavelengths of 53 prominent lines are determined with statistical uncertainties being up to 0.005 \AA . Collisional-radiative models were constructed for Si VI -- Si XII ions, which satisfactorily reproduces the experimental spectra, and helps the line identification. Calculations at different electron densities reveal that the spectra of dense plasmas are more complicate than the spectra of thin plasmas. A comparison with the Kelly database reveals a good agreement for most peak intensities, and differences for a few emission lines. Comment: 18 pages, 6 figures, and 1 table; In press of publication on ApJS July issue
03/2008;
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Y T Li,
M H Xu,
X H Yuan,
W M Wang,
M Chen,
Z Y Zheng,
Z M Sheng,
Q Z Yu,
Y Zhang,
F Liu, Z Jin,
Z H Wang,
Z Y Wei,
W Zhao,
J Zhang
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ABSTRACT: Fast electron emission from the interaction of femtosecond laser pulses with shaped solid targets has been studied. It is found that the angular distributions of the forward fast electrons are highly dependent upon the target shapes. The important roles played by the electrostatic fields built up at the non-laser-irradiated target surfaces and the collisions in the target are identified. Our two-dimensional particle-in-cell simulations with binary collisions included reproduce the main experimental observations.
Physical Review E 02/2008; 77(1 Pt 2):016406. · 2.26 Impact Factor
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Y T Li,
T T Xi,
Z Q Hao,
Z Zhang,
X Y Peng,
K Li, Z Jin,
Z Y Zheng,
Q Z Yu,
X Lu,
J Zhang
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ABSTRACT: The propagation of a tightly focused femtosecond laser pulse in air has been investigated. Unlike long-distance self-guided propagation of short laser pulses, a novel oval-like hollow distribution of the laser intensity is observed in the experiments and reproduced by the numerical simulations. The formation of the hollow structures can be explained by the interplay between ionization-induced refraction and Kerr self-focusing.
Optics Express 01/2008; 15(26):17973-9. · 3.59 Impact Factor
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Z. M. Sheng,
Y. T. Li,
M. Chen,
Y. Y. Ma,
X. H. Yuan,
M. H. Xu,
Z. Y. Zheng,
W. X. Liang,
Q. Z. Yu,
Y. Zhang,
F. Liu,
Z. H. Wang,
Z. Y. Wei, Z. Jin,
J. Zhang,
T. Nakamura,
K. Mima
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ABSTRACT: Recent experimental and theoretical studies on surface electron emission will be presented. A collimated fast electron beam was observed along the target surface irradiated by intense laser pulses up to 20TW when the laser is incident with large angles such as over 45 degree. Numerical simulations suggest that such an electron beam is formed due to the confinement of the surface quasistatic electric and magnetic fields. Meanwhile, an acceleration process similar to the inverse‐free‐electron‐laser is found to occur and is responsible for the generation of the most energetic electrons. A general formula for electron angular distributions accounting for the quasistatic electric and magnetic fields is given. In certain conditions, quasi‐monoenergetic electron beams are also produced. These results are of interest for potential applications of laser‐produced electron beams and helpful to the undersanding of the cone‐target physics in the fast ignition related experiments. © 2006 American Institute of Physics
AIP Conference Proceedings. 11/2006; 876(1):405-414.
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Y T Li,
X H Yuan,
M H Xu,
Z Y Zheng,
Z M Sheng,
M Chen,
Y Y Ma,
W X Liang,
Q Z Yu,
Y Zhang,
F Liu,
Z H Wang,
Z Y Wei,
W Zhao, Z Jin,
J Zhang
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ABSTRACT: A novel fast electron beam emitting along the surface of a target irradiated by intense laser pulses is observed. The beam is found to appear only when the plasma density scale length is small. Numerical simulations reveal that the electron beam is formed due to the confinement of the surface quasistatic electromagnetic fields. The results are of interest for potential applications of fast electron beams and deep understanding of the cone-target physics in the fast ignition related experiments.
Physical Review Letters 05/2006; 96(16):165003. · 7.37 Impact Factor
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Y T Li,
Z M Sheng,
Y Y Ma, Z Jin,
J Zhang,
Z L Chen,
R Kodama,
T Matsuoka,
M Tampo,
K A Tanaka,
T Tsutsumi,
T Yabuuchi,
K Du,
H Q Zhang,
L Zhang,
Y J Tang
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ABSTRACT: Ion acceleration inside low-density foams irradiated by ultraintense laser pulses has been studied experimentally and theoretically. It is found that the ion generation is closely correlated with the suppressed hot electron transport inside the foams. Particle-in-cell simulations suggest that localized electrostatic fields with multi peaks around the surfaces of lamellar layers inside the foams are induced. These fields inhibit hot electron transport and meanwhile accelerate ions inside the foams, forming a bulk acceleration in contrast to the surface acceleration at the front and rear sides of a thin solid target.
Physical Review E 01/2006; 72(6 Pt 2):066404. · 2.26 Impact Factor
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ABSTRACT: Filamentation formed by self-focusing of intense laser pulses propagating in air is investigated. It is found that the position of filamentation can be controlled continuously by changing the laser power and divergence angle of the laser beam. An analytical model for the process is given.
Optics Express 01/2006; 13(25):10424-30. · 3.59 Impact Factor
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J Zhang,
Y T Li,
Z M Sheng,
Y Y Ma, Z Jin,
Z L Chen,
R Kodama,
T Matsuoka,
M Tampo,
K A Tanaka,
T Tsutsumi,
T Yabuuchi
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ABSTRACT: It is suggested that bulk acceleration of ions can occur in a target with density discontinuities when hot electrons are transported through the target. A foam target just belongs to such a kind of target, which is composed of irregular lamellar layers distributed randomly. To simplify the problem, we study the interaction of a high intensity laser pulse with a target consisting of regular micro-thin layers separated with a thickness of around a micrometre. Particle-in-cell simulations suggest that localized electrostatic fields with multi-peaks around the surfaces of the thin layers inside are induced when fast electrons produced are transported through such a target. These fields inhibit hot electron transport and simultaneously accelerate ions from the thin layers inside the target, forming a bulk acceleration in contrast to the surface acceleration at the front and rear sides of a thin solid target. Bulk acceleration can produce a large number of ions of moderate energy, which may be useful for applications such as fast ignition by fast protons. Experimental evidence of bulk acceleration is found with low-density foams irradiated by ultra-intense laser pulses.
Plasma Physics and Controlled Fusion 11/2005; 47(12B):B879. · 2.42 Impact Factor
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ABSTRACT: The emission direction of outward-ejecting fast electrons generated in laser-solid interactions by 30 fs laser pulses is measured for laser intensities varying from the nonrelativistic to the relativistic. For an s-polarized incident laser beam at nonrelativistic intensities, the ejected electrons are close to the polarization direction of the laser beam. With the increase of the laser intensity, the ejected electrons are still mainly within the polarization plane, but turn away from the laser polarization direction towards the opposite direction of the incident laser beam. At relativistic intensities, electrons eject towards the direction of the reflected laser beam. The increasing ponderomotive force acceleration with the laser intensities might be responsible for the observed changes.
Physical Review E 05/2004; 69(4 Pt 2):046408. · 2.26 Impact Factor
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X Y Peng,
J Zhang, Z Jin,
T J Liang,
Z M Sheng,
Y T Li,
Q Z Yu,
Z Y Zheng,
Z H Wang,
Z L Chen,
J Y Zhong,
X W Tang,
J Yang,
C J Sun
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ABSTRACT: We investigate the angular distribution and the energy spectrum of hot electrons emitted from ethanol droplets irradiated by linearly polarized 150-fs laser pulses at an intensity of 10(16) W/cm(2). Two hot electron jets symmetrically with respect to the laser propagation direction are observed within the polarization plane. This is due to the spherical geometry of droplets in the intense laser field. The maximum energy of the hot electrons is found to be more than 600 keV. Particle-in-cell simulations suggest that the resonance absorption is the main mechanism for hot electron generation.
Physical Review E 03/2004; 69(2 Pt 2):026414. · 2.26 Impact Factor
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ABSTRACT: The resonance absorption of femtosecond pulses by liquid droplets is studied. The angular dependence of the laser absorption may be used to understand the symmetric double-lobe emission of hot electrons generated from liquid droplets. The total laser absorption fraction is found to be strongly related to the scale length of the microplasmas.
Applied Physics B 10/2003; 77(6):687-689. · 2.19 Impact Factor
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ABSTRACT: The behaviors of the blast waves produced by femtosecond laser-water interactions, and the blast waves induced by laser self-focusing in air, have been investigated using optical shadowgraphy at a maximum intensity of 1 x 10(16) W/cm(2). The temporal evolution of the blast wave launched by the water plasma can be described by a planar blast wave model including source mass. An aneurismlike structure, due to the quick propagation inside a hollow channel formed by laser self-focusing, is observed. The expansion of the channel in air is found to agree with a cylindrical self-similar blast wave solution.
Physical Review E 06/2003; 67(5 Pt 2):056403. · 2.26 Impact Factor
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ABSTRACT: The evolution of the forward density front of water-plasmas generated by ultrashort laser pulses on an air–water interface is investigated with optical diagnostics. The density front is found to move with supersonic speed at the beginning, as predicted by a hydrodynamics simulation. This plasma-expansion process is followed by a fluid mechanical process. The expansion rate gradually reduces to the acoustic speed in water. © 2002 American Institute of Physics.
Physics of Plasmas 08/2002; 9(9):4028-4031. · 2.15 Impact Factor
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ABSTRACT: In this paper, the interaction of femtosecond laser pulses with droplets microplasma at the intensity of 1016 W/cm2 is theoretically studied. Laser absorption, suprathermal electron generation, and second harmonic generation are discussed. Using an analytical model and a 2D particle-in-cell code, we find that the dominated mechanism is resonant absorption in the interaction of femtosecond laser pulses with droplets for the misrospherical geometry.
Optics Communications.
