Relativistic calculations of angular dependent photoemission time delay
  Angular dependence of photoemission time delay for the valence $np_{3/2}$ and $np_{1/2}$ subshells of Ar, Kr and Xe is studied in the dipole relativistic random phase approximation. Strong angular anisotropy of the time delay is reproduced near respective Cooper minima while the spin-orbit splitting affects the time delay near threshold. 
A. S. Kheifets, Ankur Mandal, P. C. Deshmukh, V. K. Dolmatov and S. T.   Manson
physics.atom-ph