Attosecond pulse generation by a coplanar circular and static field combination

We consider high-order harmonic generation by a field which consists of a circularly polarized laser field and a static electric field. The polarization vectors of these fields lie in the same plane. We have found that, in the case when the static electric field strength is 20-26% of the circularly polarized laser field strength, the harmonic spectrum exhibits a sharp peak for the harmonics near the cutoff. The cutoff position is higher than that of the spectrum generated by the corresponding linearly polarized laser field. The harmonics from this peak are emitted as an attosecond pulse.