Systematic analysis of an attosecond pulse generation by a sub-cycle laser field

Abstract: We investigated the influence of sub-cycle driving fields on high-order harmonic generation (HHG), with a focus on intrinsic chirp, carrier-envelope phase (CEP), and number of laser cycles. Our findings reveals that the center frequency of a laser pulse scales as $\tau^{-5/4}$ with pulse duration $\tau$, and that attochirp exhibits a similar dependence on pulse duration. Additionally, we identified CEP-specific trends in harmonic yield: it increases as $\tau^{5/4}$ for $\phi_0=0^\circ$ and decreases as $\tau^{-4.1}$ for $\phi_0= -90^\circ$. Although sub-cycle pulses can generate intense isolated attosecond pulses (IAPs), they also tend to produce higher attochirp and reduced cutoff energies. However, effective compensation for attochirp can mitigate these drawbacks, thereby increasing the capability of sub-cycle pulses to generate short-duration, high-intensity IAPs. These results offer valuable insights into HHG using sub-cycle pulses and have important implications for the advancement of ultrafast light sources and the understanding of ultrafast phenomena at the attosecond timescale.