Figure 3: Experimental spectra.

Quantitative comparison of the measured XUV spectra obtained from a 50- and 10-nm foil irradiated with (a,b) the drive pulse only and (c,d) drive and probe pulses synchronously. The backscattered XUV radiation reveals a periodically modulated spectrum when irradiating the nanometre foils with the counter-propagating pulse, whereas the signal without the probe is shot noise-dominated. In a–d dashed lines give the linear fit to the background. In c, error bars on the fit line are the maximal deviation of the background noise from the linear fit, whereas error bars at the spectral peaks are signal noise deduced from photon counting statistics. The spectra shown here are representative for a data set comprising 25 target shots, both in single- and dual-pulse configuration. No signal was observed when irradiating the foil with the probe pulse exclusively (not shown here). (e) Detector image (hot pixels removed) obtained from a 50-nm probe shot.