Tunnelling photoionization in a bichromatic laser field

Abstract
The process of electron tunnelling through a one-dimensional non-stationary barrier created by an atomic potential and an external electromagnetic bichromatic field consisting of coherent superposition of the fundamental laser field frequency and its second harmonic is considered and studied theoretically. Within the framework of the imaginary time method the analytical expression for the corresponding photoionization probability has been derived which is, in fact, the analogue of the well known Keldysh formula generalized for the bichromatic case.