Phase control in two-color multiphoton ionization of hydrogen

We consider the two-color ionization of the ground state hydrogen atom by an electromagnetic field consisting of a coherent superposition of the fundamental frequency of an UV laser and its third harmonic, with a constant relative phase. We analyze the ionization process due to the net absorption of the energy 3homega. In the intensity regime investigated here, the final continuum state is reached by the interference of two different routes: (i) the absorption of one photon from the third harmonic and (ii) the absorption of three laser photons. The influence of the harmonic phase and of the field intensity on the azimuthal angular distribution of photoelectrons is analyzed. Dichroic effects are also emphasized.