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Resolving the time when an electron exits a tunnelling barrier


The tunnelling of a particle through a barrier is one of the most fundamental and ubiquitous quantum processes. When induced by an intense laser field, electron tunnelling from atoms and molecules initiates a broad range of phenomena such as the generation of attosecond pulses1, laser-induced electron diffraction2,3 and holography2,4. These processes evolve on the attosecond timescale (1 attosecond ≡ 1 as = 10−18 seconds) and are well suited to the investigation of a general issue much debated since the early days of quantum mechanics5,6,7—the link between the tunnelling of an electron through a barrier and its dynamics outside the barrier. Previous experiments have measured tunnelling rates with attosecond time resolution8 and tunnelling delay times9. Here we study laser-induced tunnelling by using a weak probe field to steer the tunnelled electron in the lateral direction and then monitor the effect on the attosecond light bursts emitted when the liberated electron re-encounters the parent ion10. We show that this approach allows us to measure the time at which the electron exits from the tunnelling barrier. We demonstrate the high sensitivity of the measurement by detecting subtle delays in ionization times from two orbitals of a carbon dioxide molecule. Measurement of the tunnelling process is essential for all attosecond experiments where strong-field ionization initiates ultrafast dynamics10. Our approach provides a general tool for time-resolving multi-electron rearrangements in atoms and molecules11,12,13—one of the key challenges in ultrafast science.

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Figure 1: Electron trajectories contributing to the recollision process.
Figure 2: Schematic description of the two-colour gates.
Figure 3: Reconstruction of the ionization and recollision times.
Figure 4: Gating two-channel tunnel ionization in aligned carbon dioxide molecules.

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  1. Hentschel, M. et al. Attosecond metrology. Nature 414, 509–513 (2001)

    Article  ADS  CAS  Google Scholar 

  2. Spanner, M., Smirnova, O., Corkum, P. B., Ivanov, M. & Yu Reading diffraction images in strong field ionization of diatomic molecules. J. Phys. B 37, L243–L250 (2004)

    Article  ADS  CAS  Google Scholar 

  3. Meckel, M. et al. Laser-induced electron tunneling and diffraction. Science 320, 1478–1482 (2008)

    Article  ADS  CAS  Google Scholar 

  4. Huismans, Y. et al. Time-resolved holography with photoelectron waves. Science 331, 61–64 (2011)

    Article  ADS  CAS  Google Scholar 

  5. Büttiker, M. & Landauer, R. Traversal time for tunneling. Phys. Rev. Lett. 49, 1739–1742 (1982)

    Article  ADS  Google Scholar 

  6. Steinberg, M. A., Kwiat, P. G. & Chiao, R. Y. Measurement of the single-photon tunnelling time. Phys. Rev. Lett. 71, 708–711 (1993)

    Article  ADS  CAS  Google Scholar 

  7. Landauer, R. & Martin Barrier interaction time in tunneling. Rev. Mod. Phys. 66, 217–228 (1994)

    Article  ADS  Google Scholar 

  8. Uiberacker, M. et al. Attosecond real-time observation of electron tunnelling in atoms. Nature 446, 627–632 (2007)

    Article  ADS  CAS  Google Scholar 

  9. Eckle, P. et al. Attosecond ionization and tunneling delay time measurements in helium. Science 322, 1525–1529 (2008)

    Article  ADS  CAS  Google Scholar 

  10. Krausz, F., Ivanov, M. & Yu Attosecond physics. Rev. Mod. Phys. 81, 163–234 (2009)

    Article  ADS  Google Scholar 

  11. Schultze, M. et al. Delay in photoemission. Science 328, 1658–1662 (2010)

    Article  ADS  CAS  Google Scholar 

  12. Smirnova, O. et al. High harmonic interferometry of multi-electron dynamics in molecules. Nature 460, 972–977 (2009)

    Article  ADS  CAS  Google Scholar 

  13. Walters, Z. B. & Smirnova, O. Attosecond correlation dynamics during electron tunnelling from molecules. J. Phys. B 43, 161002 (2010)

    Article  ADS  Google Scholar 

  14. Keldysh, L. V. Ionization in the field of a strong electromagnetic wave. Sov. Phys. JETP 20, 1307–1314 (1965)

    Google Scholar 

  15. Perelomov, M. A., Popov, S. V. & Terent’ev, M. V. Ionization of atoms in an alternating electric field: II. Sov. Phys. JETP 24, 207 (1967)

    ADS  Google Scholar 

  16. Corkum, P. B. Plasma perspective on strong field multiphoton ionization. Phys. Rev. Lett. 71, 1994–1997 (1993)

    Article  ADS  CAS  Google Scholar 

  17. Salières, P. et al. Feynman’s path-integral approach for intense-laser-atom interactions. Science 292, 902–905 (2001)

    Article  ADS  Google Scholar 

  18. Pfeiffer, A. N. et al. Attoclock reveals natural coordinates of the laser-induced tunnelling current flow in atoms. Nature Phys. 8, 76–80 (2012)

    Article  ADS  CAS  Google Scholar 

  19. Baker, S. et al. Probing proton dynamics in molecules on an attosecond time scale. Science 312, 424–427 (2006)

    Article  ADS  CAS  Google Scholar 

  20. Mairesse, Y. et al. Attosecond synchronization of high-harmonic soft X-rays. Science 302, 1540–1543 (2003)

    Article  ADS  CAS  Google Scholar 

  21. Dudovich, N. et al. Measuring and controlling the birth of attosecond XUV pulses. Nature Phys. 2, 781–786 (2006)

    Article  ADS  CAS  Google Scholar 

  22. Chirilă, C. C., Dreissigacker, I., van der Zwan, E. V. & Lein, M. Emission times in high-order harmonic generation. Phys. Rev. A 81, 033412 (2010)

    Article  ADS  Google Scholar 

  23. Shafir, D. et al. Atomic wavefunctions probed through strong-field light-matter interaction. Nature Phys. 5, 412–416 (2009)

    Article  ADS  CAS  Google Scholar 

  24. Lewenstein, M., Balcou, Ivanov, M., Yu, L’Huillier, A. & Corkum, P. B. Theory of high-harmonic generation by low-frequency laser fields. Phys. Rev. A 49, 2117–2132 (1994)

    Article  ADS  CAS  Google Scholar 

  25. Dahlström, J. M., L’Huillier, A. & Mauritsson, J. Quantum mechanical approach to probing the birth of attosecond pulses using a two-colour field. J. Phys. B 44, 095602 (2011)

    Article  ADS  Google Scholar 

  26. Haessler, S. et al. Attosecond imaging of molecular electronic wavepackets. Nature Phys. 6, 200–206 (2010)

    Article  ADS  CAS  Google Scholar 

  27. Murray, R., Spanner, M., Patchkovskii, S., Ivanov, M. & Yu Tunnel ionization of molecules and orbital imaging. Phys. Rev. Lett. 106, 173001 (2011)

    Article  ADS  Google Scholar 

  28. Tong, X. M., Zhao, Z. X. & Lin, C. D. Probing molecular dynamics at attosecond resolution with femtosecond laser pulses. Phys. Rev. Lett. 91, 233203 (2003)

    Article  ADS  CAS  Google Scholar 

  29. Niikura, H. et al. Probing molecular dynamics with attosecond resolution using correlated wave packet pairs. Nature 421, 826–829 (2003)

    Article  ADS  CAS  Google Scholar 

  30. Mairesse, Y. et al. High harmonic spectroscopy of multichannel dynamics in strong-field ionization. Phys. Rev. Lett. 104, 213601 (2010)

    Article  ADS  CAS  Google Scholar 

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N.D. acknowledges the Minerva Foundation, the Israeli Science Foundation and the Crown Center of Photonics for financial support. N.D. and O.S. acknowledge the German-Israeli Foundation, and D.S. acknowledges support from the Converging Technologies Fellowship of the Israeli Ministry of Science. H.S. is supported by the Adams Fellowship Program of the Israel Academy of Sciences and Humanities. O.S. acknowledges the support of the DFG grant Sm292/2-1, and M.Yu.I. acknowledges the support of the EPSRC programme grant EP/I032517/1. Y.M. acknowledges financial support from the ANR (ANR-08-JCJC-0029 HarModyn) and the Conseil Regional d’Aquitaine (20091304003 AttoMol). M.I. acknowledges support of the EPSRC Programme Grant EP/I0325171/1.

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D.S., H.S., B.D.B., M.D. and N.D. designed, performed and analysed the experiment. Y.M. contributed to the analysis. M.Yu.I. and O.S. developed the theory and performed the calculations of harmonic spectra. S.P. provided the quantum chemistry input for the calculations. All authors contributed to writing the manuscript.

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Correspondence to Nirit Dudovich.

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The authors declare no competing financial interests.

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Shafir, D., Soifer, H., Bruner, B. et al. Resolving the time when an electron exits a tunnelling barrier. Nature 485, 343–346 (2012).

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