High photon flux table-top coherent extreme-ultraviolet source
Hädrich S, Klenke A, Rothhardt J, Krebs M, Hoffmann A, Pronin O, Pervak V, Limpert J, Tünnermann A 2014 High photon flux table-top coherent extreme-ultraviolet source Nat Photon 8, 779-783.
Abstract
High harmonic generation (HHG) enables extreme-ultraviolet radiation with table-top set-ups. Its exceptional properties, such as coherence and (sub)-femtosecond pulse durations, have led to a diversity of applications. Some of these require a high photon flux and megahertz repetition rates, for example, to avoid space charge effects in photoelectron spectroscopy. To date, this has only been achieved with enhancement cavities. Here, we establish a novel route towards powerful HHG sources. By achieving phase-matched HHG of a megahertz fibre laser we generate a broad plateau (25 eV–40 eV) of strong harmonics, each containing more than 1 × 1012 photons s–1, which constitutes an increase by more than one order of magnitude in that wavelength range. The strongest harmonic (H25, 30 eV) has an average power of 143 μW (3 × 1013 photons s–1). This concept will greatly advance and facilitate applications in photoelectron or coincidence spectroscopy, coherent diffractive imaging or (multidimensional) surface science.