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Free-electron lasers (FELs) operating in the extreme ultraviolet region are unique laser sources giving access, for the first time, to the exploration of nonlinear processes in this spectral range [1].Recently, FERMI@Elettra came into operation providing users with XUV pulses characterized by an excellent pulse to pulse energy stability (<10 %) and with the possibility to finely tune the photon energy in the range 19-62 eV.