A deep vacuum-ultraviolet (VUV) light source is highly desirable for time-resolved studies involving highlying excited or ionized states of molecules. Such a source can provide one-photon excitation of these states and thus simplify the studied dynamics. We have realized a femtosecond VUV source based on low-order harmonic generation in a semi-infinite gas cell. A 400-nm driver is used to generate the third (133nm, 9.3 eV) and fifth order (80 nm, 15.5 eV) harmonics. We have implemented a two-colour single-photon pump-probe scheme combining the harmonic source with 266-nm femtosecond pulses. The beamline is coupled with a velocity map imaging (VMI) spectrometer to detect energy and momentum distributions of charged particles.
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