Development of a 10 kHz high harmonic source up to 140 eV photon energy for ultrafast time-, angle-, and phase-resolved photoelectron emission spectroscopy on solid targets.

We present a newly developed high harmonic beamline for time-, angle-, and carrier-envelope phase-resolved extreme ultraviolet photoemission spectroscopy on solid targets for the investigation of ultrafast band structure dynamics in the low-fs to sub-fs time regime. The source operates at a repetition rate of 10 kHz and is driven by 5 fs few-cycle near-infrared laser pulses generating high harmonic radiation with photon energies up to 120 eV at a feasible flux. The experimental end station consists of a complementary combination of photoelectron detectors which are able to spectroscopically address electron dynamics both in real and in k-space. The versatility of the source is completed by a phase-meter which allows for tracking the carrier-envelope phase for each pulse and which is synchronized to the photoelectron detectors, thus enabling phase sensitive measurements on the one hand and the selection of single attosecond pulses for ultimate time resolution in pump-probe experiments on the other hand. We demonstrate the applicability of the source by an angle- and carrier-envelope phase-resolved photoemission measurement on a tungsten (110) surface with 95 eV extreme ultraviolet radiation.

Sub-phonon-period compression of electron pulses for atomic diffraction.

Visualizing the rearrangement of atoms in a wide range of molecular and condensed-matter systems requires resolving picometre displacements on a 10-fs timescale, which is achievable using pump-probe diffraction, given short enough pulses. Here we demonstrate the compression of single-electron pulses with a de Broglie wavelength of 0.08 ångström to a full-width at half-maximum duration of 28 fs or equivalently 12-fs root-mean square, substantially shorter than most phonon periods and molecular normal modes. Atomic resolution diffraction from a complex organic molecule is obtained with good signal-to-noise ratio within a data acquisition period of minutes. The electron-laser timing is found to be stable within 5 fs (s.d.) over several hours, allowing pump-probe diffraction at repetitive excitation. These measurements show the feasibility of laser-pump/electron-probe scans that can resolve the fastest atomic motions relevant in reversible condensed-matter transformations and organic chemistry.