Ultrafast processes in matter, such as the electron emission following light absorption, can now be studied using light pulses of attosecond duration in the extreme ultraviolet spectral range. However, the short temporal duration of these pulses implies a large energy spread of the photoelectrons according to Heisenberg’s uncertainty principle. Indeed, the lack of spectral resolution due to the use of short pulses has raised issues in the interpretation of the experimental results in comparison with theoretical calculations. Here, we present new experimental results on the long-standing problem of photoionization time delays in neon atoms that were originally measured by Schultze and co-workers using isolated attosecond pulses 1. Using our alternative approach 2, based on attosecond pulse trains, we gain both high temporal and spectral resolution by photoelectron interferometry. This allows us to spectrally disentangle direct ionization from ionization with shake-up, in which a second electron is left in an excited state, and obtain excellent agreement with theoretical calculations based on diagrammatic many-body perturbation theory 3. In this way we have solved a 7-year-old puzzle in attosecond science.
1. Schultze, M. et al. Delay in Photoemission. Science (80-. ). 328, 1658–1662 (2010).
2. Isinger, M. et al. Photoionization in the time and frequency domain. Science (80-. ). (2017). doi:10.1126/science.aao7043
3. Dahlström, J. M., Carette, T. & Lindroth, E. Diagrammatic approach to attosecond delays in photoionization. Phys. Rev. A 86, 61402 (2012).