  High-order harmonic generation in gas targets is a widespread scheme used to
produce extreme ultraviolet radiation, however, it has a limited microscopic
efficiency. Macroscopic enhancement of the produced radiation relies on
phase-matching, often only achievable in quasi-phase-matching arrangements. In
the present work we numerically study quasi-phase-matching induced by
low-intensity assisting fields. We investigate the required assisting field
strength dependence on the wavelength and intensity of the driving field,
harmonic order, trajectory class and period of the assisting field. We comment
on the optimal spatial beam profile of the assisting field.
