High-Order Harmonic Generation in the Presence of Static Electric Field

We study the effects of the static electric field on the high-order harmonic generation (HOHG). It is found that the presence of the static electric field breaks the inversion and reflection symmetry, as a result, the HOHG spectrum exhibits a double plateau structure. Furthermore, the cutoff of the HOHG is no longer corresponding to the maximum kinetic energy the ionized electron can obtain from the laser field. Instead, it corresponds to the maximum kinetic energy of the electron with one return.