Energy- and angle-resolved photoelectron spectra of above-threshold ionization and detachment

Abstract

We analyze strong-laser-field induced above-threshold ionization and above-threshold detachment processes within the strong-field approximation. Energy and angular distribution of photoelectrons are presented for two cases: (1) high-order above-threshold ionization of electrons from neutral atoms by a linearly polarized laser field and (2) above-threshold detachment of electrons from negative ions by a bicircular laser field. In particular, for the case (1) we compare the results obtained using a long pulse with the flat-top spatial intensity distribution in the laser focus with the results obtained using the Gaussian distribution. We also analyze the intensity-dependent resonant-like enhancements. We show that the position and shape of these enhancements strongly depend on the atomic ground state parity. The bicircular field of the case (2) consists of two counter-rotating circularly polarized fields having the frequencies rω and sω with integer r and s. The properties of the photoelectron spectra generated by such bicircular field are illustrated using an ω–4ω example. The spectra obtained are explained in terms of the interference of partial detachment amplitudes which correspond to different complex solutions of the saddle-point equations.