FIG. 9.

The spectrum of a typical transmitted pair of SASE pulses (green) at the excitation ((a) and (c)) and emission ((b) and (d)) transitions and their ensemble average (blue). Panels (a) and (b) correspond to the transmitted spectrum of a propagation distance of z = 0.15 mm and (c) and (d) z = 1 mm. Due to the strong resonant absorption of the pump radiation, a larger dynamic range of the spectrometer setup is required for the longer medium.