Ardana-Lamas, FLambert, GTrisorio, AVodungbo, BMalka, VZeitoun, PHauri, C P2015-03-122015-03-122015-03-12201310.1088/1367-2630/15/7/073040https://infoscience.epfl.ch/handle/20.500.14299/112350WOS:000322110600002We present a bright and coherent soft x-ray source based on high harmonic generation delivering up to 10(10) photons per second centered at 120 eV within an 80 eV bandwidth. The source profits from fully phase-matched harmonic generation in an unmodulated hollow waveguide. Under these conditions, the resulting high harmonic spectrum is shown to be flat-top up to the cutoff photon energy and in line with the theoretical single-atom response. The source is characterized in view of seeding a free-electron laser and is shown to overcome the free-electron laser noise floor for wavelengths as short as 8.9 nm. This opens the perspective toward direct high harmonic seeding of a free-electron laser at soft x-ray wavelengths.text::journal::journal article::research article