Fig. 4: Sketch of the ISRS process and of the FEL layout.
From: Element- and enantiomer-selective visualization of molecular motion in real-time
a Pulse scheme of the experiment with the relevant energy levels: The 4.7 eV pump pulse (purple pulse) generates a coherent superposition of vibrational levels in the HOMO by impulsive stimulated Raman scattering (ISRS). These modes are then probed with element-selectivity by the soft X-ray pulse (light purple pulse) tuned to the carbon K-edge. b The experimental layout. A 786 nm femtosecond laser pulse is split and delivered to an optical parametric amplifier (OPA) where it is up converted to generate the ~4.76 eV pulse that initiate the Free Electron Laser process, as well as a frequency-tripling (THG) to generate the 4.7 eV pump pulse. The seeded electron bunch is propagated through a chain of apple II undulators, allowing control of the polarization and energy of the soft X-ray photons. An ionization chamber (IOM) and a spectrometer are used to record on a pulse-to-pulse base the characteristics of FEL beam. An ellipsoidal mirror is ultimately used to focus the FEL beam on the sample.
