Photoemission with high-order harmonics: A tool for time-resolved core-level spectroscopy

A setup for femtosecond time-resolved photoelectron spectroscopy of solid surfaces is presented. The photon energies for core-level spectroscopy experiments are created by high-order harmonic generation from infrared 120-femtosecond laser pulses focused in a Ne gas jet. The present experimental realization allows the sample, located in an ultrahigh-vacuum chamber, to be illuminated by ∼106∼106 65-eV photons per laser pulse at a 10 Hz repetition rate. The spectral width of a single harmonic is 0.77 eV (FWHM), and a few harmonics are selected by specially designed Mo/Si multi-layer mirrors. Photoelectrons from the sample are collected by a large-solid-angle time-of-flight electron spectrometer based on a parabolic-grid reflector. Results from experiments probing the Bi 5d5d core-levels are presented, and the results of preliminary pump-probe experiments are described.