Polarization effects in two-photon nonresonant ionization of argon with extreme-ultraviolet and infrared femtosecond pulses

We report the results of experimental and theoretical investigations of the two-color, two-photon ionization of Ar atoms, using femtosecond pulses of infrared laser radiation in combination with its extreme-ultraviolet harmonics. It is shown that the intensities of the photoelectron lines resulting from the absorption of photons from both fields strongly depend both on the respective phases of the fields and on atomic quantities such as the asymmetry parameter. These phases, which are notoriously difficult to measure, can be estimated by changing the polarization state of the laser radiation.