Recent measurements of time delays during tunnelling of cold atoms through an optically created potential barrier have fuelled an ongoing debate about possible time delays during light-induced tunnelling of an electron from an atom. Yet, such a delay—whether it is present or not—is only one quantity characterizing the tunnelling wavepacket, whilst the underlying dynamics are richer. Here we show how to complement photo-electron detection in laser-induced tunnelling by measuring the light emitted by the tunnelling electron—the so-called Brunel radiation. Using a combination of single- and two-colour driving fields, we identify the all-optical signatures of the reshaping of the tunnelling wavepacket as it emerges from the tunnelling barrier and moves away from the core. This reshaping includes not only an effective time delay but also the time-reversal asymmetry of the ionization process, which we describe theoretically and observe experimentally. We show how both delay and reshaping are mapped onto the polarization properties of the Brunel radiation, with different harmonics behaving as different hands of a clock moving at different speeds. The all-optical detection may also allow time-resolved measurements of optical tunnelling in condensed matter systems on the attosecond time scale.
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Source data are available for this paper. All other data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request. Source data are provided with this paper.
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I.B., A.D. and U.M. thank the Deutsche Forschungsgemeinschaft (DFG) (projects BA 4156/4-2, MO 850-19/2) as well as the Cluster of Excellence PhoenixD (EXC 2122, project ID 390833453) for financial support. O.G.K., I.A.N., N.A.P. and D.E.S. thank the Russian Science Foundation (grant no. 21-49-00023) and National Natural Science Foundation of China (12061131010) for support. S.S. acknowledges support by the Qatar National Research Fund (grant NPRP 12S-0205-190047) and HPC resources from GENCI (grant no. A0080507594). Á.J.G. acknowledges funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement no. 101028938. M.I. acknowledges support by the DFG priority programme QUTIF under grant agreement IV 152/6-2 and funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement no 899794.
The authors declare no competing interests.
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Babushkin, I., Galán, Á.J., de Andrade, J.R.C. et al. All-optical attoclock for imaging tunnelling wavepackets. Nat. Phys. 18, 417–422 (2022). https://doi.org/10.1038/s41567-022-01505-2