Femtosecond photoelectron and photoion spectrometer with vacuum ultraviolet probe pulses

摘要

We describe a setup to study ultrafast dynamics in gas-phase molecules usingtime-resolved photoelectron and photoion spectroscopy. The vacuum ultraviolet(VUV) probe pulses are generated via strong field high-order harmonicgeneration from infrared femtosecond laser pulses. The band pass characteristicin transmission of thin indium (In) metal foil is exploited to isolate the$9^{\text{th}}$ harmonic of the 800 nm fundamental (H9, 14 eV, 89 nm) from allother high harmonics. The $9^{\text{th}}$ harmonic is obtained with highconversion efficiencies and has sufficient photon energy to access the completeset of valence electron levels in most molecules. The setup also allows fordirect comparison of VUV single-photon probe with 800 nm multi-photon probewithout influencing the delay of excitation and probe pulse or the beamgeometry. We use a magnetic bottle spectrometer with high collection efficiencyfor electrons, serving at the same time as a time of flight spectrometer forions. Characterization measurements on Xe reveal the spectral width of H9 to be$190\pm60$ meV and a photon flux of $\sim1\cdot10^{7}$ photons/pulse afterspectral filtering. As a first application, we investigate the S$_1$ excitationof perylene using time-resolved ion spectra obtained with multi-photon probingand time-resolved electron spectra from VUV single-photon probing. The timeresolution extracted from cross-correlation measurements is $65\pm10$ fs forboth probing schemes and the pulse duration of H9 is found to be $35\pm8$ fs.