Phase dependence of three-colour two-photon ionization of hydrogen

We consider a ground-state hydrogen atom interacting with a three-colour el ectromagnetic field, taken as the superposition of a fundamental frequency omega and two consecutive odd harmonics of order 2p - 1 and 2p + 1 (p great er than or equal to 2 and integer), with constant relative phase difference s. We study in the lowest-order perturbation theory the process of ionizati on due to the net absorption of energy 2ph omega. The ionization rate is co ntrolled by the relative phase difference delta between the harmonics, whic h modifies the interference terms. We present an analysis of both the angul ar electron distribution and the total rate, which shows that the interfere nce effects are influenced by the order of the harmonics and their intensit y ratio.