Fig. 7.

Photoelectron spectra from the high-harmonic generation in argon and neon. For spectral filtering the neon (argon) harmonics, an XUV multilayer mirror centred at 65 eV (49 eV) was used. In both cases, photoelectron peaks stemming from the tungsten valence band and the 4f core state are clearly visible and separated by the 4f 7/2 binding energy of 31.4 eV⁴². To account for the different excitation energies, the photoelectron spectra are shifted by 22.3 eV with respect to each other (note different x-axes). Results in argon are shown in black; neon in red