Ultrafast Electron and Spin Dynamics in Nickel Probed With Femtosecond X-Ray Pulses

We present the first X-ray absorption spectrum over an entire absorption edge using femtosecond pulses from a synchrotron-based slicing source. An ultrafast laser pulse excited a nickel film, and a succeeding X-ray pulse from the BESSY femtoslicing facility probed the Ni L₃-edge. By choosing either linear or circular X-ray polarization, the spectra represent snapshots of the electronic or the magnetic state, respectively, with an exposure time of about 100 fs. We find an almost instantaneous response of the electronic system to the laser pulse, and provide a first direct measurement of the quenching of magnetic moments within 120 fs.