New Journal of Physics
We analyze the role of group-velocity matching (GVM) in the macroscopic build up of the high-harmonic signal generated in gas targets at high pressures. A definition of the walk-off length, associated with GVM, in the non-perturbative intensity regime of high-harmonic generation is given. Semiclassical predictions based on this definition are in excellent agreement with full quantum simulations. We demonstrate that group velocity matching is a relevant factor in high harmonic generation and the isolation of attosecond pulses driven by long wavelength lasers and preferentially selects contributions from the short quantum trajectories.
Hernández-García, C; Popmintchev, T; Murnane, M.M.; Kapteyn, H.C.; Plaja, L; Becker, A; and Jaron-Becker, A, "Group velocity matching in high-order harmonic generation driven by mid-infrared lasers" (2016). Physics Faculty Contributions. 94.