Photoelectron spectra and transition mechanisms of a hydrogen atom in the n = 2 state under circularly polarized pulses in the barrier suppression ionization (BSI) regime, found by solving the time-dependent Schrödinger equation, are presented in detail. The photoelectron peak emerges from low-energy, in contrast to being centered at higher energy in the case of ionization from the ground state. We show that the magnetic quantum number dependence of photoelectron angular distributions on initial states yields 3- and 2-band structures for 2p - and 2p 0 in zenith angle, respectively, and 1-band structures for both 2p + and 2s. The intermediate transition pathways from these initial states to the corresponding final states are also revealed.
- barrier suppression ionization
- circularly polarized pulse
- photoelectron angular distribution
- transition mechanism