Spectral extension and energy redistribution during high-harmonic generation in gas driven by a coherent combination of near-IR and mid-IR intense laser fields
Phys. Rev. A 113, 013516 – Published 12 January, 2026
DOI: https://doi.org/10.1103/f3bg-3z26
Abstract
We experimentally demonstrate the extension and energy redistribution of a high-order harmonic spectrum generated by the near-IR 1.24-µm 100-fs laser pulse coherently combined with the long-wavelength 4.5-µm 200 fs field. This synthesized multicycle field allows formation of up to 200 eV soft-x-ray continuum in He gas under moderate driving field intensity at the level of . The observed extension is caused by the activation of the cutoff trajectory of the second return while maintaining high photoemission efficiency via the enhanced ionization probability. The decrease in the driving pulses duration and the increase of a long-wavelength field strength will allow further extension of the harmonic spectrum, opening opportunities for the time-resolved K-edge absorption spectroscopy in the water window and keV spectral ranges.
