Gating of high-order harmonics generated by incommensurate two-color mid-IR laser pulses

We experimentally demonstrate a new technique for the temporal gating of high-order harmonic generation, based on the mixing of two mid-infrared laser pulses coming from optical parametric amplifiers, at wavelengths of 1.35 and 1.75 mu m, respectively. Both parallel and perpendicular configurations of the polarization directions were investigated. Results obtained in xenon and argon show continuous spectra with a significant cutoff extension, up to 160 eV. These outcomes demonstrate the possibility of extending the two-color gating technique for the generation of isolated attosecond bursts to a mid-infrared laser source and are, to our knowledge, the first experimental demonstration of the gating on a single half-cycle of high-order harmonics driven by laser pulses longer than 30 fs.