Phase Effects in Two-Color Multiphoton Processes

Abstract

There has been considerable interest over the past few years in the interactions of atoms and molecules with intense, short pulsed lasers. Measurements and calculations of ionization rates and photoemission rates have been reported for many wavelengths and intensities for single frequency laser fields. More recently, the effects of the presence of a second, intense laser field have been considered. Predictions that ionization dynamics can be controlled using two lasers with a fixed phase relationship between the them have been realized in experiments by Chen and Elliot1 and by Muller, et al.2 In both experiments the rate for multiphoton ionization was shown to depend on this phase. Muller, et al. also showed that the ATI (above threshold ionization) photoelectron energy distributions were also affected. Here we report calculations of the two-color ionization of hydrogen that reproduce these observed phase sensitive effects. We also present angular distributions for the photoelectrons and their variation with the relative phase between the lasers. In addition these calculactions address the question of the magnitude of the ponderomotive shift of the ionization potential caused by the combined laser fields.