Absorption Enhancement of an Electric Quadrupole Transition of Cesium Atoms in an Evanescent Field

Abstract

We have observed for the first time reflection spectra of an electric quadrupole transition for the cesium atom ($6\text{ }^{2}S_{1/2}\mathrm{\text{\ensuremath{-}}}5\text{ }^{2}D_{5/2}$) line at an angle of incidence from ${\ensuremath{\theta}}_{c}\ensuremath{-}11.9$ to ${\ensuremath{\theta}}_{c}+107.5\text{ }\mathrm{m}\mathrm{r}\mathrm{a}\mathrm{d}$, where ${\ensuremath{\theta}}_{c}$ is the critical angle for total reflection. From a comparison with the calculated absorption in the attenuated total reflection, the oscillator strengths for $s$ and $p$ polarizations were found to increase with an increase in the angle of incidence by a factor up to 1.5 at ${\ensuremath{\theta}}_{c}+83.8\text{ }\mathrm{m}\mathrm{r}\mathrm{a}\mathrm{d}$ and 2.4 at ${\ensuremath{\theta}}_{c}+107.5\text{ }\mathrm{m}\mathrm{r}\mathrm{a}\mathrm{d}$, respectively, in the experiment. The dependences of the observed enhancement on the angle of incidence were in good agreement with the calculated ones for the oscillator strength of the quadrupole transition in the evanescent light.