Berlin 2018 – scientific programme

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O: Fachverband Oberflächenphysik

O 79: Poster: Ultrafast Electron and Spin Dynamics at Interfaces

O 79.8: Poster

Wednesday, March 14, 2018, 18:15–20:30, Poster A

A novel setup for XUV-based time-resolved ARPES at 500 kHz repetition rate — M. Puppin, C. Nicholson, P. Xian, W. Windsor, Y. Deng, J. Feldl, C. Monney, M. Wolf, •L. Rettig, and R. Ernstorfer — Fritz-Haber-Institut der MPG, Faradayweg 4-6, 14195 Berlin

We present a novel setup for time- and angle-resolved photoemission spectroscopy (trARPES) based on ultrashort extreme ultraviolet (XUV) laser source with 0.5 MHz repetition rate. The source is driven by an optical parametric chirped pulse amplifier (OPCPA) based on a hybrid fiber-slab amplifier system. The near-infrared OPCPA output is frequency-upconverted sequentially: frequency-doubling to 3.1 eV photon energy is followed by 7th harmonic generation (21.7 eV) in a dense noble gas jet. After spectral filtering, an XUV pulse with 20 fs pulse duration, a bandwidth of ∼100 meV and a photon flux exceeding 10¹¹ photons/s is available for trARPES.

We demonstrate the capabilities of the setup by mapping the excited state structure of bulk WSe₂ 100 fs after optical excitation with 3.1 eV photons throughout the Brillouin zone and compare the results to DFT band structure calculations. Furthermore, in TbTe₃ we investigate the closing of the charge density wave energy gap and unfolding of the band structure in both occupied an unoccupied states after excitation with 1.55 eV photons. Our experimental setup allows the observation of occupied and transiently populated unoccupied states and their dynamics in the whole Brillouin zone, and the determination of direct and indirect band gaps within a single experiment.