A Few-Femtosecond UV Light Source for the Realtime Tracking of Coherent Electron and Nuclear Dynamics in Molecules

Few-femtosecond ultraviolet (UV) light pulses are required for the real-time monitoring of electron dynamics occurring in electronically-excited neutral molecules [1]. We report the design and implementation of a compact, integrated microfluidic chip for broadband UV generation. The chip features a differentially pumped glass cell (Fig. 1a) that enhances gas confinement and improves the conversion efficiency of third harmonic generation driven by few-cycle temporally-reshaped near-infrared (NIR) pulses [2]. The resulting UV pulses (typical spectra are shown in Fig. 1b and 1c) were subsequently combined with few-femtosecond near-infrared (NIR) probe pulses to study the ultrafast excited-state dynamics of acetone. Previous studies have shown that resonant excitation to the Rydberg states of acetone via a 2-UV photon transition is followed by ultrafast relaxation via non-adiabatic crossings between the electronic states [3]. However, these studies have lacked the temporal resolution to fully resolve the dynamics occurring on a sub-10 fs timescale. Here, we take advantage of the unprecedented resolution offered by the UV source described above to monitor the ultrafast dynamics of (excited) acetone. Data were acquired using a double-sided spectrometer capable of simultaneous mass spectrometry and electron velocity map imaging.