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Interpreting attoclock measurements of tunnelling times

Abstract

Resolving in time the dynamics of light absorption by atoms and molecules, and the electronic rearrangement this induces, is among the most challenging goals of attosecond spectroscopy. The attoclock is an elegant approach to this problem, which encodes ionization times in the strong-field regime. However, the accurate reconstruction of these times from experimental data presents a formidable theoretical task. Here, we solve this problem by combining analytical theory with ab initio numerical simulations. We apply our theory to numerical attoclock experiments on the hydrogen atom to extract ionization time delays and analyse their nature. Strong-field ionization is often viewed as optical tunnelling through the barrier created by the field and the core potential. We show that, in the hydrogen atom, optical tunnelling is instantaneous. We also show how calibrating the attoclock using the hydrogen atom opens the way to identifying possible delays associated with multielectron dynamics during strong-field ionization.

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Figure 1: The attoclock set-up.
Figure 2: Comparison of numerical and analytical calculations.
Figure 3: Offset angles θ extracted from photoelectron spectra as a function of intensity.
Figure 4: Attoclock spectra for long and short range potentials.
Figure 5: Reconstruction of ionization times.

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Acknowledgements

We acknowledge stimulating discussions with U. Keller and A. Landsman. J.K., O.S. and M.I. acknowledge support of the EU Marie Curie ITN network CORINF, Grant Agreement No. 264951. F.M. and O.S. acknowledge support of the DFG project SM 292/3-1, S.S. and M.I. acknowledge support of the EPSRC Programme Grant EP/I032517/1, M.I. acknowledges the support of the United States Air Force Office of Scientific Research program No. FA9550-12-1-0482, O.S., L.T. and J.K. acknowledge support of the DFG grant SM 292/2-3. A.K. and I.I. acknowledge support of the Australian Research Council Grant DP120101805. A.Z. and A.S. acknowledge support from the DFG through excellence cluster Munich Center for Advanced Photonics (MAP) and from the Austrian Science Foundation project ViCoM (F41). O.S., M.I., F.M. and A.S. acknowledge the support of the European COST Action XLIC CM1204, H.G.M. acknowledges the hospitality of the Max Born Institute.

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L.T., J.K. and O.S. derived the ARM method and performed the analytical study. F.M., H.G.M., M.I., A.Z., A.S., A.K., I.I. and S.S. performed the numerical simulations and checked the convergence and consistency of the results. F.M., O.S. and M.I. analysed the origins of negative ionization times. O.S. directed and coordinated the research. L.T., M.I. and O.S. wrote the paper. All authors discussed the results and provided contributions to the text of the manuscript.

Corresponding author

Correspondence to Olga Smirnova.

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The authors declare no competing financial interests.

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Torlina, L., Morales, F., Kaushal, J. et al. Interpreting attoclock measurements of tunnelling times. Nature Phys 11, 503–508 (2015). https://doi.org/10.1038/nphys3340

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