Attosecond Pulses from a Solid Driven by a Synthesized Two-Color Field at Megahertz Repetition Rate

Probing coherent quantum dynamics in light–matter interactions at the microscopic level requires high-repetition-rate isolated attosecond pulses (IAPs) in pump–probe experiments. To date, the generation of IAPs has been mainly limited to the kilohertz regime. In this work, we experimentally achieve attosecond control of extreme-ultraviolet (XUV) high harmonics in the wide-bandgap dielectric MgO, driven by a synthesized field of two femtosecond pulses at 800 and 2000 nm with relative phase stability. The resulting quasi-continuous harmonic plateau with ∼9 eV spectral width centered around 16.5 eV photon energy can be tuned by the two-color phase and supports the generation of an IAP (∼700 attoseconds), confirmed by numerical simulations based on the three-band semiconductor Bloch equations. Leveraging the high-repetition-rate driver laser, the moderate intensity requirements of solid-state high-harmonic generation, and band-structure-induced spectral enhancement, we achieve IAP production at an unprecedented megahertz repetition rate, paving the way for compact all-solid-state XUV sources for IAP generation.