Time Resolved 3D momentum imaging of Molecular Dynamics with VUV pulse pairs

We report progress on an apparatus for running UV-VUV pump-probe experiments with Cold Target Recoil Ion Momentum Spectroscopy (COLTRIMS) for investigating ultrafast dynamics in polyatomic molecules upon VUV excitation. We loosely focus a high-power 400 nm pulsed laser into an argon filled 10 cm long gas cell to create a high-flux, coherent third harmonic (133nm) photon beam (10$^{\mathrm{9}}$ photons/shot) via High Harmonic Generation (HHG). A custom, in-vacuum split-mirror interferometer creates VUV - VUV/UV pulse pairs for pump-probe studies with a relative delay range up to several picoseconds, and 170 as resolution. In the experimental end-station, the beam is back-focused into a supersonic jet by a spherical mirror at the exit of a COLTRIMS spectrometer, which measures the 3D momenta of charged particles that are produced.