The asymmetry of negative ion photodetachment in a bichromatic laser field

The angular (polar) asymmetry of ejection of a photoelectron produced in a negative ion multiphoton detachment process in a linearly polarized bichromatic electromagnetic (EM) field consisting of coherent superposition of the fundamental laser field frequency and its second harmonic is studied theoretically and the physical mechanism underlying this phenomenon is explained in the frame of perturbation theory for EM interaction. Two model potentials, both the simplest one-dimensional zero-range potential and a three-dimensional nonlocal separable Yamaguchi potential, are used for description of the detached electron interaction with its parent residual atomic core. For either of both exactly solvable models used it is shown that in general, in such an asymmetric (with respect to the replacement e --> -e of the EM field polarization vector) bichromatic field the ejection of detached photoelectrons is also asymmetric with respect to the replacement p --> -p of the detached photoelectron momentum. The degree of this asymmetry of photodetachment depends mostly on the relative phase shift Phi between the harmonics and the ratio of their electric field strengths and it does not vanish even for Phi = pi/2 or 3 pi/2, i.e., even when the bichromatic field is symmetric.