Splitting of isolated attosecond pulses via phase-mismatched spectral minima in macroscopic HHG driven by single-cycle mid-infrared laser pulses

We propose a method to split isolated attosecond pulses (IAPs) using phase-mismatch-induced spectral minima in high-order harmonic generation driven by single-cycle mid-infrared laser pulses. We demonstrate that the spectral minimum shifts to higher harmonic orders with increasing gas pressure but is insensitive to the laser's carrier-envelope phase. At higher laser intensities, the double-minimum harmonics can reach the hundred-eV range. The resulting IAP profiles, obtained through spectral synthesis and spatial integration of low-divergence far-field high harmonics, exhibit clear splitting. This work offers a tunable scheme for shaping IAPs in the extreme ultraviolet to soft X-ray spectral regions.