Fig. 2: Experimental setup.
From: Bright continuously tunable vacuum ultraviolet source for ultrafast spectroscopy
a The experimental setup for tunable high-order harmonic generation (HHG) implemented into the HHG beamline at ELI Beamlines14. The infra-red laser beam is apertured by a motorized iris and focused by a spherical mirror at almost normal incidence on a Kr gas target. A beta-barium borate (BBO) crystal in the beam path is used for the second harmonic generation, and a thin dichroic mirror is used to separate SH from IR. Thin metallic filters separate the generated VUV from residual pump light. The partially reflected pump beam from the metallic filters is characterized by a UV-NIR spectrometer. A wavelength-calibrated flat-field spectrometer can be used to characterize the VUV beam, or the beam is sent to the user end-station MAC. The MAC station61 is set up to investigate He nanodroplets, including a cryo-cooled pulsed He source, heated cells for doping the droplets with evaporated substances, and a velocity map imaging detector for either electrons or ions detection. b Typical spectra obtained when VUV pulses are generated by HHG from both the fundamental and SH as a drive, i.e., without the dichroic mirror (red line), and when only the SH pulses are used to drive HHG, i.e., with the dichroic mirror (blue line).
