Singlesub−50−attosecondpulse generation from chirp-compensated harmonic radiation using material dispersion

Abstract

A method for obtaining a single $\mathrm{sub}\text{\ensuremath{-}}50\text{\ensuremath{-}}\text{attosecond}$ pulse using harmonic radiation is proposed. For the generation of broad harmonic radiation during a single half-optical cycle, atoms are driven by a femtosecond laser pulse with intensity above the saturation intensity for optical field ionization and hence experience a large nonadiabatic increase of the laser electric field between optical cycles. Although the chirped structure of the harmonic radiation imposes a limit on the minimum achievable pulse duration, we demonstrate that its positive chirp can be compensated by the negative group delay dispersion of an appropriately selected x-ray filter material, used also for the spectral selection, resulting in a single attosecond pulse with a duration less than $50\phantom{\rule{0.3em}{0ex}}\mathrm{as}$.