Probing atomic and molecular targets by intense bicircular counter-rotating laser fields

Abstract

We present an ab initio study of strong-field ionization of H and by two-colour bicircular counter-rotating 1ω–2ω laser pulses containing two and ten optical cycles at the fundamental frequency corresponding to a wavelength of 800 nm. We address effects of laser intensity, pulse duration and in the case of of alignment on photoelectron momentum distributions (PMDs). In the long pulse limit, as expected from a simple classical picture, the PMDs of H and of aligned perpendicular to the polarization plane show a three-fold symmetry imposed by the bicircular laser field. Compared with the expectation for the positions of the peaks in this three-fold structure, we observe off-set angles that depend on the photoelectron energy as well as the laser intensity. For , the symmetry in the PMDs is broken by the anisotropic molecular potential at molecular alignment not perpendicular to the plane of laser polarization. In the short pulse limit, the PMDs are sensitive to the carrier envelope phase of the laser field.