High-order harmonics and supercontinua formed by a weak optical pump in the presence of an extreme terahertz field

We show that in the presence of an extreme terahertz (THz) field additional weak optical frequency range can modulate ionization probability and thereby generate high-order harmonics. The THz pump suppresses recollisions, also fully suppressing recollision-based Nevertheless, harmonics are effectively generated via alternative mechanism, so-called Brunel based on subsequent acceleration driving (but not reabsorption). Using ab initio simulations for hydrogen atom short few-cycle driver, we appearance a coherent carrier-envelope-phase-insensitive supercontinuum formed by such harmonics, compressible into isolated pulse with 100-attosecond-scale duration.