Two-Color Multiphoton Ionization of Atoms Using High-Order Harmonic Radiation

Laser-assisted single-photon ionization of an atomic system can be observed in the simultaneous presence of a strong low-frequency laser field and of one of its (weaker) high-order harmonics. Typical photoelectron spectra associated to such two-color processes are simulated via the numerical solution of the time-dependent Schrödinger equation, for a hydrogen atom in the presence of both fields. We address the question of the interplay between this laser-assisted process and above-threshold ionization. Our results show that new sets of two-color experiments can be performed at moderate laser intensities easily attainable by currently operated sources.