Absolute Rb one-color two-photon ionization cross-section measurement near a quantum interference

Abstract

We observe destructive interference in the ground-state Rb two-photon ionization cross section when the single photon energy is tuned between the $5S\ensuremath{\rightarrow}5P$ and $5S\ensuremath{\rightarrow}6P$ transition energies. The minimum cross section is $5.9(1.5)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}52}\phantom{\rule{0.3em}{0ex}}{\text{cm}}^{4}\phantom{\rule{0.3em}{0ex}}\mathrm{s}$ and it occurs at a wavelength of $441.0(3)\phantom{\rule{0.3em}{0ex}}\text{nm}$ (in vacuo). Relative measurements of these cross sections are made at various wavelengths by counting ions produced when magneto-optically trapped Rb atoms are exposed to light from a tunable pulsed laser. This relative curve is calibrated to an absolute cross-section measurement at $532\phantom{\rule{0.3em}{0ex}}\text{nm}$ using the trap loss method. A simple calculation agrees reasonably with our results.