Ultrafast broadband diagnostics of the filling of the $s$ band at the two-photon femtosecond laser excitation of a gold film

The transmission of near infrared femtosecond laser pulses (wavelength of 800 nm) and supercontinuum radiation (300–750 nm) generated by them through a 50-nm gold film immersed in water has been experimentally studied at the power of focused laser radiation in the range of 1–10 GW. An increase in the excitation intensity is accompanied by the blueshift of the edge of the extinction band of the film, which is attributed to the filling of electronic states of the $s$ band with a low density of states caused by two-photon interband transitions from $d$ bands with a high density of states.