An isolated attosecond pulse emission of He atom driven by the midinfrared laser field with polarization gating

We investgate the high-order harmonic generation(HHG) emission of helium atom exposed to the midinfrared fields (λ = 2128 nm) with polarization gating by the strong field approximation(SFA) method. It is shown that the cut-off of HHG from helium atom driven by the fields is extended, and the supercontinuum spectra on the platuea near the cut-off are obtained. As a result, an isolated 44.5 as pulse is generated by superposing the some range of the supercontinuum spectra. In order to explain the emission process of HHG, we also perform the time-frequency analysis. Our results indicate that the emission of attosecond pulses outside the gating are suppressed when the polarization gating is used, thus a single isolated ultrashort pulse can be generated. (authors)