Few-cycle strong-field ionization of atomic hydrogen with elliptically polarized light.

We consider strong-field ionization of atomic hydrogen by elliptically polarized light in the long-wavelength regime (800~nm). By solving the time-dependent Schr\"odinger equation, we analyze the ionization spectra at various peak intensities up to $4 \times 10^{14}\,$W/cm$^2$. The calculations are performed with the length and velocity forms of the electric dipole operator. In particular, we compare the extreme cases of circularly and linearly (studied in~[1]) polarized light. Starting from an oriented atomic state, we also consider the dynamics responsible for circular dichroism~[2], from the multiphoton to the tunneling regime. A model based on the strong-field approximation is employed in an attempt to predict the variation of the dichroism as a function of the laser peak intensity. Finally, we analyze the tunneling time for photo-ionization in the strong-field regime. [1] A. N. Grum-Grzhimailo, B. Abeln, K. Bartschat, D. Weflen, and T.~Urness, Phys.\ Rev. A~{\bf 81} (2010) 043408. [2] M. Ilchen {\it et al.}, Phys.\ Rev.\ Lett.~{\bf 118} (2017) 013002.