Fig. 2
Setup for efficient high average power HHG. The Yb-fibre laser is frequency doubled in a BBO crystal. Afterwards, the 515 nm light is coupled into a gas-filled capillary for spectral broadening and is subsequently compressed using a chirped mirror compressor. The spectral and temporal pulse characteristic at 51 W of average power is shown in the insets (a) and (b). HHG is achieved by focussing the short visible pulses to a diameter of 33 μm (1/e2 intensity, c) into a krypton gas jet. Separation of the driving laser and the XUV light, as well as additional attenuation of the XUV radiation (in order not to saturate the detector) is done using two glass plates in Brewster’s angle and additional aluminium filters. At the end, the XUV beam is characterized spectrally and spatially using a flat field spectrometer equipped with an XUV CCD camera