Ultrafast x-ray absorption near edge spectroscopy of FeO using a laboratory based femtosecond x-ray source.

Ultrafast time-resolved x-ray absorption near edge spectroscopy (XANES) experiment was performed on a magnetite (FeO) film using a femtosecond laser plasma x-ray source delivering Bremsstrahlung radiation. Ultrafast temporal evolution of the XANES of FeO following an excitation by an infra-red (IR) laser pulse was observed in a pump-probe scheme. The Fe K x-ray absorption edge shifts towards low energy upon IR excitation as much as 12 eV, which is mainly attributed to the charge transfer between the Fe ions. The shift in the absorption edge occurred within about 150 fs, typical time of non-thermal electronic redistribution. The charge transfer also causes an ultrafast increase in the IR transmission in the similar time scale.