High photon flux table-top coherent extreme-ultraviolet source

摘要

High harmonic generation (HHG) enables extreme-ultraviolet radiation with table-top set-ups1. 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 × 10~(12) 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 (3×10~(13) photons s~(-1)). This concept will greatly advance and facilitate applications in photoelectron or coincidence spectroscopy, coherent diffractive imaging or (multidimensional) surface science.