About spatial asymmetry of photoelectron emission in a bichromatic laser field

The angular (polar) asymmetry of ejection of photoelectron produced at negative ion multiphoton detachment process in a linearly polarized bichromatic electromagnetic field consisting of coherent superposition of fundamental laser field frequency and its second harmonic is studied theoretically within frame of perturbation theory on EM interaction. For particular case of exactly solvable model of zero-range potential used for description of detached electron interaction with its parent residual atomic core in such spatially asymmetric bichromatic field the ejection of detached photoelectrons is also generally asymmetric (in respect of the detached photoelectron momentum replacement p --> -p). The degree of this asymmetry depends mostly on relative phase shift Phi between the harmonies, the ratio of the harmonic electric field strengths and angle between the harmonics field polarization vectors. In particular, this latter asymmetry of photoelectron emission is not vanishing even at phase shifts Phi = pi/2 or 3pi/2 (i.e., even when the considered ionizing bichromatic field has always spatially symmetric temporal dependence) and the physical mechanism underlying this paradoxical phenomenon is explained thoroughly.