Two-photon decay in gold atoms following photoionization with synchrotron radiation

We have measured two-photon decay of single K vacancies in gold atoms following photoionization with synchrotron radiation. Our results for the $2\overrightarrow{s}1s$ and $3\overrightarrow{d}1s$ two-photon transitions determine the rates for two-photon decay when the photons share the transition energy equally and have opening angles near $\theta =\pi /2.\mathrm{}$ These results are compared with nonrelativistic calculations for H-like Au ions and with theoretical and experimental results on lighter atoms.