Abstract
SynopsisIn contrast to one-photon transitions and non-resonant multiphoton transitions, time delay in resonant multi-photon electron emission can exhibit large positive and negative values that have no scattering equivalent, due to the interference of multiple ionization paths.
Highlights
When a wave packet scatters off a short-range potential, it acquires a delay, compared with a reference free wave
We have shown that, when intermediate resonances are populated in two-photon ionization processes, the usual relationships between one-photon induced ionization time delay, electron wave-packet group delay, Wigner time delay, and multiphoton time delay no longer hold
This is because the one-photon dipole coupling between the ground state and the continuum, DEg, vanishes at a specific energy, so that one-photon time delays cannot be defined as the energy derivative of the corresponding matrix element
Summary
When a wave packet scatters off a short-range potential, it acquires a delay, compared with a reference free wave. The probe photon is exchanged first, whereas the resonant path involves the radiative transition between the intermediate metastable state and the final continuum In this case, h ∂E arg DE(2g) differs from τW by a new sharply peaked resonant term with no scattering counterpart. The relative strength of the resonant and nonresonant paths is controlled by the probe frequency ωIR By varying this frequency and keeping the pump frequency (and all other parameters) constant, it is possible to radically alter the group delay τ (2) of the two-photon photoelectron wave packet.
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