When interacting with a molecule or an atom, an intense ultra short laser
field periodically drives electron wave packets away and back to the parent
ion. At each return, the electron bunch may recombine to the initial
electronic state producing an XUV light burst of attosecond duration. The
characteristics of the XUV radiation is therefore directly mapped out from
the temporal and spectral structure of the electrons wave packets while
recolliding. Controlling the laser field to allow only one recollision
event is the key to produce a single attosecond pulse.
Here, for the first time, we have unambiguously achieved the temporal confinement of XUV harmonic radiation down to an isolated attosecond burst using the technique of polarization gating with (CEP) phase-stabilized few-optical-cycle driving pulses . The signature of a single attosecond pulse emission has been observed in two gases, argon and neon, for three different broad spectral ranges, 25-40 eV in argon and 35-70 eV or 50-100 eV in neon. While earlier work was limited to attosecond pulse bandwidth of few eV hence to pulse longer than 100 as, polarization gating provides access to the full bandwidth of the recolliding EWP and potentially enables the generation of isolated pulses of few attoseconds. Isolated attosecond pulses are thus becoming accessible in new spectral and temporal ranges and will benefit to new attosecond science such as time resolved tomographic imaging of electron wave packet motion or electron-electron interaction dynamics at the atomic unit time scale.
 I. Sola, E. Mével, L. Elouga, E. Constant, V. Strelkov, L. Poletto, P . Villoresi, E. Benedetti, J.-P. Caumes, S. Stagira, C. Vozzi, G. Sansone and M. Nisoli, "Controlling attosecond electron dynamics by phase-stabilized polarization gating", Nature Physics, 2, 319 (2006)
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