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Yu.M. Mikhailova, V.T. Platonenko
Low intensity of attosecond pulses obtained in the process of high-order harmonic generation by atoms in laser beams is one of the most serious problems facing the attosecond technology. In this connection the possibility to obtain high-intensity single attosecond pulses in the interaction of ultrarelativistic laser pulses with laser-induced overcritical plasmas, shown theoretically by several authors [N.M. Naumova et al, 92, 063902 (2004); Yu.M. Mikhailova et al, JETP Lett. 81, 571 (2005); T. Baeva et al, Phys. Rev. E 74, 065401(R) (2006)], is promising and important. The proposed methods for isolation of single attosecond pulses, which are necessary for experimental resolving attosecond processes in molecules and atoms, from the trains of attopulses include using few-cycle exciting pulses together with spectral or spatial filtering as well as gating by means of time-dependent polarization of laser pulse. With 2D pic simulations we have analyzed the possibilities to obtain trains and isolated attosecond pulses in the process of high harmonic generation in overcritical plasmas irradiated by few-cycle ultrarelativistic laser pulse. Under appropriate conditions, single attosecond electromagnetic pulses with the intensity as much as 1% of the exciting laser intensity can be obtained by spectral filtering of light reflected or transmitted through a thin overdense plasma slab. As is shown, the increase in the laser intensity leads to the increase in the efficiency of attosecond pulse generation. Moreover, varying the laser intensity, thickness and density of the plasma slab, one can obtain single attosecond pulses with various spectra, which can include frequencies several hundred times higher than the laser frequency (the photon energies up to several kilo electron volts). |
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