Quantum Beat Photoelectron Imaging Spectroscopy of Xe in the VUV

Time-resolved pump-probe measurements of Xe, pumped at 133 nm and probed at 266 nm, are presented. The pump pulse prepared a long-lived hyperfine wave packet in the Xe $5{p}^{5}(^{2}P_{1/2}^{\ensuremath{\circ}})6s{\phantom{\rule{0.16em}{0ex}}}^{2}{[1/2]}_{1}^{\ensuremath{\circ}}$ manifold ($E=77\phantom{\rule{0.16em}{0ex}}185\phantom{\rule{0.16em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}=9.57\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$). The wave packet was monitored via single-photon ionization and velocity map photoelectron images were measured. The images provide angle- and time-resolved data which, when obtained over a large time window (900 ps), constitute a precision quantum-beat spectroscopy measurement of the hyperfine state splittings. Additionally, analysis of the full photoelectron image stack provides a quantum-beat imaging modality, in which the Fourier components of the photoelectron images correlated with specific beat components can be obtained. This may also permit the extraction of isotope-resolved photoelectron images in the frequency domain, in cases where nuclear spins (hence beat components) can be uniquely assigned to specific isotopes (as herein), and also provides phase information relating to the ionization dynamics. The information content of both raw and inverted image stacks is investigated, suggesting the utility of the Fourier analysis methodology in cases where images cannot be inverted.