Control Of Photoemission Delay In Resonant Two-Photon Transitions

Abstract

The photoelectron emission time delay τ associated with one-photon absorption, which coincides with half the Wigner delay τW experienced by an electron scattered off the ionic potential, is a fundamental descriptor of the photoelectric effect. Although it is hard to access directly from experiment, it is possible to infer it from the time delay of two-photon transitions, τ(2), measured with attosecond pump-probe schemes, provided that the contribution of the probe stage can be factored out. In the absence of resonances, τ can be expressed as the energy derivative of the one-photon ionization amplitude phase, τ=∂EargDEg, and, to a good approximation, τ=τ(2)-τcc, where τcc is associated with the dipole transition between Coulomb functions. Here we show that, in the presence of a resonance, the correspondence between τ and ∂EargDEg is lost. Furthermore, while τ(2) can still be written as the energy derivative of the two-photon ionization amplitude phase, ∂EargDEg(2), it does not have any scattering counterpart. Indeed, τ(2) can be much larger than the lifetime of an intermediate resonance in the two-photon process or more negative than the lower bound imposed on scattering delays by causality. Finally, we show that τ(2) is controlled by the frequency of the probe pulse, ωIR, so that by varying ωIR, it is possible to radically alter the photoelectron group delay.

Publication Date

4-26-2017

Publication Title

Physical Review A

Volume

95

Issue

4

Document Type

Article

Personal Identifier

scopus

DOI Link

https://doi.org/10.1103/PhysRevA.95.043426

Socpus ID

85018325055 (Scopus)

Source API URL

https://api.elsevier.com/content/abstract/scopus_id/85018325055

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