Fig. 2: Time-resolved photoelectron spectroscopy from tungsten 4f and valence band.

a XUV spectrum generated in neon (black line) and XUV mirror reflectivity (blue filled area). The XUV spectrum is cut off at 72 eV by a 300 nm Al foil filter. b Static photoelectron spectrum with photoelectrons emitted from the tungsten valence band (blue filled area) and the deeper-bound 4f state (red filled area). The comb-like appearance of the excitation spectrum is imprinted in the photoelectron spectrum. Sideband positions are indicated by dashed lines (likewise in c and d). c RABBITT spectrogram. Due to depletion, not only the sidebands (predominantly blue) but also the high harmonic peaks (predominantly red) oscillate in intensity. A distinct anomaly in the regularity of the pattern is observed around 62 eV. For better visibility, the displayed spectrogram is background subtracted (see “Methods”). The inset shows the intensities of the sidebands at 59.5 and 61.9 eV (circles), and their fits (lines). d Comparison of sideband delays with the electron transport time to the crystal surface. The blue area shows transport times predicted by the final-state group velocities. A classical free-electron propagation results in the red line. Sideband delays extracted from c are indicated by black circles. Sideband delays from another RABBITT spectrogram using argon harmonics (see Supplementary Fig. 2a) is indicated by orange circles. The error bars represent the SD over all traces in each dataset (see “Methods”). As only relative photoemission delays are extracted from the spectrograms, an arbitrary delay offset has been added to each dataset to match the calculated delays.