Isolated sub-100 attosecond pulse generation driven by a multi-cycle chirped laser pulse and a polarization gating

We theoretically investigate the high-order harmonic generation driven by the combination of a multi-cycle nonlinear chirped laser pulse and a polarization gating. On the one hand, the x-component of the polarization gating enlarges the asymmetry of the pulse centre of the chirped laser field, which leads to the extension of the cutoff of the high-order harmonic spectrum; on the other hand, only a few cycles of the combination field centre remain linearly polarized due to the existence of the y-component of the polarization gating, which helps to generate the continuum spectrum. Therefore, in the high-order harmonic spectrum, a very broad continuum spectrum appears even in the multi-cycle regime, from which an isolated sub-100 as pulse could be obtained.