Analysis of interference effects in the direct photodetachment from H− in a two-color laser pulse

We extend the adiabatic saddle-point (SP) method of Shearer et al (2011 Phys. Rev. A 84 033409) to study electron detachment from H− exposed to a two-color few-cycle linearly polarized laser pulse that consists of a fundamental frequency and its half harmonic. We show that the photoelectron angular distributions (PADs) are dominantly contributed from several central SPs that correspond to the strongest part of two-color pulses. By separately calculating the PADs formed in the different detachment steps, the rich oscillatory patterns in the PADs can be mainly attributed to the interference effects of coherent quantum wave packets in the classical propagation step of detachment processes, whereas the interference effects in the quantum tunneling step are weaker because the corresponding shape of the PADs is almost independent of the relative time delay of two pulses. The interference effects in the classical propagation step are also confirmed by the angle-dependent averaged cosine value of phase differences for each two dominant SPs. We find that the PADs of H− ions can be efficiently controlled by properly adjusting the relative time delay and intensity ratio of a controlling field to the driving field. (paper)