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Pulse-duration control of subcycle multiband electron dynamics extends the high-harmonic cutoff in a light-driven insulator
We demonstrate pathway-selective control of extreme-ultraviolet high-harmonic generation by jointly tuning laser pulse duration (5 - 29 fs) and intensity (0.8 – 74 TW/cm2). Many-cycle pulses at moderate intensities, ∼ 6 TW/cm2, promote cumulative carrier transfer over successive optical cycles, progressively accessing higher conduction bands. In contrast, few-cycle, high-intensity, ∼ 22 TW/cm2, pulses drive subcycle multiband dynamics that reach 25 - 50 eV photon energies before decoherence can suppress coherent emission. These results reveal pulse duration and intensity as decisive control knobs for high-harmonic emission, opening a route to band-structure-guided pulse design for higher energy extreme-ultraviolet light sources.