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Figure 2
An illustration of how the spectrometer is exploited for pump–probe measurements. A laser beam (red) enters nearly collinearly with the XFEL beam (blue). Due to the small angle between the two rays, the effective propagation time of the pulses differs. Any spectral variation as a function of the delay is monitored in the 1D spectrometer. The spatial resolution along the incident beam corresponds to a few femtoseconds time resolution of the delay. The box in the top part of the figure schematically shows the pulses and their temporal delay along the propagation of the XFEL beam at different points along the interaction medium. Spectra recorded at three different positions, corresponding to three different delays, are shown in the bottom part of the figure. Typically, the measurements by the 1D spectrometer are combined with measurements by an in-line spectrometer, which directly monitors transient absorption and stimulated emission, indicated to the right in the figure. |