Angular distributions and quantum beats of photoelectrons from resonant two-photon ionization of lithium

Angular distributions of photoelectrons from resonant two-photon ionization via the $2p$ ${}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}$ or $2p$ ${}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}$ state of lithium have been measured. The quantum beats of hyperfine levels strongly affect the angular distribution. Three microscopic parameters are extracted: the ratio of the radial matrix elements from $2p$ excited states to $l=0\mathrm{} \mathrm{and} 2$ final states, the difference of the phase shifts of the continuum electrons in final channels, and a time-dependent parameter for hyperfine interaction. The experimental results agree with theoretical quantum-defect calculation and extrapolated bound-state data.