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Attosecond timing of photons and electrons one by one

February 3, 2020

Experimental Principle and Quantum Path Disentanglement

a) Schematic of the photoionization pathways contributing to a sideband (SB) in the RABBITT experiment in Helium. (b)-(d) Experimental anisotropy parameters (β_0, β_2, β_4) of the angle resolved RABBITT spectra. Insets: angular distribution terms.

We perform angle resolved photoelectron spectroscopy in helium using a COLTRIMS detector [3] following the RABBITT scheme [4]. As illustrated in Figure 1a, four quantum pathways contribute to each sideband (SB), comprising the pathways with angular quantum numbers s->p->s and s->p->d for absorption and emission [5]. This allows us to reduce the angular dependence of the measured RABBITT spectra to a set of three anisotropy parameters (Figure 1b- d) for which analytic expression can be determined within second order perturbation theory. A simultaneous fit of the sideband oscillations of the anisotropy parameters then retrieves both, the amplitudes and the relative phases of the four contributing quantum pathways. Further, comparing the relative phase between pathways following the absorption of the same XUV photon, both XUV and Wigner phase cancel out and, hence, the contribution of the cc- transitions to the photoionization phase can be isolated. Further details on Ultrafast Laser Physics, ETH Zürich  here.

Reference: J. Fuchs, N. Douguet, S. Donsa, F. Martin. J. Burgdörfer, L. Argenti, L. Cattaneo, U. Keller , "Time delays from one- photon transitions in the continuum, " Optica, vol. 7, No. 2, pp. 154- 161, 2020, (DOI: 10.1364/OPTICA.378639)
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