Extended Data Fig. 2: Typical streaking spectrogram measured for I/W(110) at 32% of the saturated iodine surface coverage and its reconstruction.

The first column shows the experimental data, the second column the results of the reconstruction algorithm and the third column their difference. The residual mainly consists of background independent of the XUV−NIR-delay, which is cancelled during the retrieval by differentiating along the delay axis. The three rows focus, from top to bottom, on the streaking of the valence, W4f and I4d photoemission peaks. The XUV−NIR-delay difference between consecutive spectra in the spectrogram is 200 as. The photoemission delay results extracted from this sample spectrogram are \({\rm{\Delta }}{\tau }_{{\rm{W}}4f-{\rm{I}}4d}=81\hspace{1pt}{\rm{as}}\) and \({\rm{\Delta }}{\tau }_{{\rm{Valence}}-{\rm{I}}4d}=14\hspace{1.5pt}{\rm{as}}\).