Fig. 3
High harmonic generation at 1 MHz. a Generated high harmonic spectrum using krypton with a backing pressure of 0.4 bar and a 430 μm gas nozzle, together with the corresponding average power in each harmonic line. The highest average power in the 11th harmonic of 12.9 ± 3.5 mW corresponds to a photon flux of 3 · 1015 ph/s. b Fourier limited pulse duration of the 11th harmonic at 26.5 eV of 3.4 fs (FWHM) as well as the simulated high harmonic signal (5.1 fs, supplement). c Long term measurement of the average power in the 11th harmonic at 26.5 eV over a time period of 30 min every 0.2 s, showing an rms deviation of 2.6%. d Spatial lineout of the whole XUV beam with a corresponding Gaussian fit