Coherent narrowband light source for ultrafast photoelectron spectroscopy in the 17–31 eV photon energy range
Riccardo Cucini, Tommaso Pincelli, G. Panaccione, Damir Kopić, Fabio Frassetto, Paolo Miotti, Gian Marco Pierantozzi, Simone Peli, A. Fondacaro, Aleksander De Luisa, Alessandro De Vita, Pietro Carrara, Damjan Krizmancic, Daniel T. Payne, Federico Salvador, Andrea Sterzi, Luca Poletto, F. Parmigiani, G. Rossi, Federico Cilento
Abstract
Here, we report on a novel narrowband High Harmonic Generation (HHG) light source designed for ultrafast photoelectron spectroscopy (PES) on solids. Notably, at 16.9 eV photon energy, the harmonics bandwidth equals 19 meV. This result has been obtained by seeding the HHG process with 230 fs pulses at 515 nm. The ultimate energy resolution achieved on a polycrystalline Au sample at 40 K is ∼22 meV at 16.9 eV. These parameters set a new benchmark for narrowband HHG sources and have been obtained by varying the repetition rate up to 200 kHz and, consequently, mitigating the space charge, operating with ≈3×107 electrons/s and ≈5×108 photons/s. By comparing the harmonics bandwidth and the ultimate energy resolution with a pulse duration of ∼105 fs (as retrieved from time-resolved experiments on bismuth selenide), we demonstrate a new route for ultrafast space-charge-free PES experiments on solids close to transform-limit conditions.