Absolute photoionization cross-section measurement of selectively excited magnesium

Abstract

We report the first absolute measurement of the cross section for photoionization from a selectively excited short-lived atomic singlet state. Employing two simultaneous tunable laser pulses, the $3s3p^{1}P_{1}^{o}\ensuremath{-}3{p}^{2}^{1}S_{0}$ autoionization resonance in MgI was found to have a peak cross section of (8\ifmmode\pm\else\textpm\fi{}4)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}16}$ ${\mathrm{cm}}^{2}$ at $\ensuremath{\lambda}300.9$ nm and a half-width of 2.5 nm. The measured ratio of the cross sections to the $3{p}^{2}^{1}S_{0}$ and $^{1}D_{2}$ states was 14:1. The effect of polarization of the lasers has been investigated and shown to provide a means of identifying the angular momentum states of autoionizing levels.