Coherent continuum generation above 100 eV driven by an ir parametric source in a two-color scheme

High-order harmonics were generated in a two-color scheme exploiting an infrared parametric source with self-stabilization of the carrier-envelope phase. A significant cutoff extension was observed with respect to single color, 800 nm driving pulses at comparable peak intensities. Exploiting the wavelength tuning of the parametric source in the 1.5-1.6 mu m range, a continuous xuv spectrum extending from 36 to 70 eV was generated in krypton. A broader xuv continuum, extending beyond 100 eV, was observed in argon. These results represent a step forward in the extension of attosecond science toward the soft x-rays region and open new perspectives in the investigation of quantum effects in atoms and molecules.