Autoionization rates of core-excited magnesium Rydberg atoms in electric fields using the core fluorescence as a reference

Abstract

$[{\mathrm{M}}^{+*}]nl$ core-excited Rydberg states of the alkaline-earth-metal atoms can decay by electronic autoionization ($[{\mathrm{M}}^{+*}]nl\ensuremath{\rightarrow}{\mathrm{M}}^{+}+\ensuremath{\varepsilon}{l}^{\ensuremath{'}}$) or by fluorescence of the core ($[{\mathrm{M}}^{+*}]nl\ensuremath{\rightarrow}[{\mathrm{M}}^{+}]nl+h\ensuremath{\nu}$). The two processes can be detected separately by monitoring the prompt ${\mathrm{M}}^{+}$ autoionization yield and the delayed pulsed-field-ionization yield of the $[{\mathrm{M}}^{+}]nl$ Rydberg states. Whereas the former process strongly depends on the principal ($n$) and orbital angular-momentum ($l$) quantum numbers, the latter is independent of $n$ and $l$ because it is essentially a property of the ion core. We present an experimental study of the competition between autoionization and core fluorescence in $[\mathrm{Ne}]3{p}_{3/2}nl$ core-excited Rydberg states of Mg atoms and of its dependence on $n$ and weak electric fields. We analyze the experimental results using a kinetic model, from which we extract the electronic-autoionization rates by using the ${\mathrm{Mg}}^{+}\phantom{\rule{4pt}{0ex}}3{p}_{3/2}--3{s}_{1/2}$ core fluorescence (${\ensuremath{\tau}}_{\mathrm{fl}}=3.8$ ns) as an internal clock. The autoionization rate of the $3{p}_{3/2}n{d}_{3/2}$ ($J=3$) and of the fully Stark-mixed $3{p}_{3/2}nk\phantom{\rule{4pt}{0ex}}(m=0,\ifmmode\pm\else\textpm\fi{}2)$ series are $[1.9\ifmmode\times\else\texttimes\fi{}{10}^{16}/{{n}^{*}}^{3}]\phantom{\rule{4pt}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$ and $[8(3)\ifmmode\times\else\texttimes\fi{}{10}^{15}/{n}^{4}]\phantom{\rule{4pt}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$, which would translate for the lowest Rydberg states ($3d$ with ${n}^{*}=2.62$) to autoionization rates of $\ensuremath{\sim}{10}^{15}$ and $\ensuremath{\sim}{10}^{14}\phantom{\rule{4pt}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$, respectively, as fast as Auger decay processes.