Extended Data Fig. 5: Verification of the XFWM signal at 200 mbar.
From: Coherent nonlinear X-ray four-photon interaction with core-shell electrons
Spectral maps recorded in the same experimental conditions but with different number and position of holes opened in the spatial mask. a, Standard measurement configuration, that is, three holes of the spatial mask open, only one incoming beam closed. b,c, Photon energy maps measured closing two of the incoming beams. An indicative scheme of each mask and beam block configuration is shown as inset in the three 2D spectral maps. All measurements were done with the same gas pressure of 200 mbar and 25 fs r.m.s. pulse duration.
