Fig. 1

Experimental setup. The laser beam (\(\lambda =1.315\ \upmu {\rm{m}}\), \(I=4.55\times 1{0}^{15}\ {\rm{W}}{{\rm{cm}}}^{-2}\)) irradiates a 1.5–\(\upmu {\rm{m}}\)–thick Cu foil at normal incidence. The Cu K–shell emission is observed by spatially resolving crystal spectrometer and a temporally resolving streak camera