Bulletin of the American Physical Society

Electric field-induced changes in the autoionization branching ratios of the 6p{sub 1/2}nd J = 3 states of barium

William E. Cooke, G. T. Xu

Published May 1, 1993• 0 citations

Abstract

We report a measurement of the branching ratio for production of 5d{sub 3/2} ions in various m{sub j} states following the autoionization of the (6{sub p1/2}nd{sub 5/2})J=M{sub J}=3 states of barium in an electric field. By detecting the population in different ion states, rather than the electron distribution, we are able to measure the decay routes even in the presence of an electric field. These branching ratios show pronounced new structure, even at fields as low as 30 V/cm.

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Bulletin of the American Physical Society

Electric field-induced changes in the autoionization branching ratios of the 6p{sub 1/2}nd J = 3 states of barium

William E. Cooke, G. T. Xu

Published May 1, 1993• 0 citations

OpenAlex

Abstract

Related papers

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The authors have measured the population in each of the 5d 3/2 (m j ) ion states following autoionization of the (6p 3/2 nd) J=MJ=3 state by using a circularly polarized laser to excite the Ba + 5d 3/2 to 6p 1 2/ transition, and observing the polarized fluorescence of the Ba + 6p 1/2 to 6s 1/2 transition. The branching ratios for autoionization into each of the 5d 3/2 in l j channels can be related to these ion populations by using angular momentum algebra. The fractions of ions found in the m j =+3/2, +1/2, -1/2 and -3.2 state of the 5d 3/2 ion states were 5.9(+or-2.6)%, 4.5(+or-1.9)%, 3.2(+or-1.3)% and 1.9(+or-0.6)% respectively. This method can easily be generalized to measure the branching ratio for autoonization into other ion states.The authors have measured the population in each of the 5d 3/2 (m j ) ion states following autoionization of the (6p 3/2 nd) J=MJ=3 state by using a circularly polarized laser to excite the Ba + 5d 3/2 to 6p 1 2/ transition, and observing the polarized fluorescence of the Ba + 6p 1/2 to 6s 1/2 transition. The branching ratios for autoionization into each of the 5d 3/2 in l j channels can be related to these ion populations by using angular momentum algebra. The fractions of ions found in the m j =+3/2, +1/2, -1/2 and -3.2 state of the 5d 3/2 ion states were 5.9(+or-2.6)%, 4.5(+or-1.9)%, 3.2(+or-1.3)% and 1.9(+or-0.6)% respectively. This method can easily be generalized to measure the branching ratio for autoonization into other ion states.

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Electric-field–induced interferences in autoionizing resonances

E. B. Saloman, J. Cooper, Daniel E. Kelleher

We have observed the effect of electric fields on the 5d9p ${}^{3}$ ${P}_{1}$ \ifmmode^\circ\else\textdegree\fi{} barium resonance above the first ionization threshold. This relatively broad autoionizing level is nearly degenerate with a much narrower level of opposite parity. At moderate fields the sharp level produces an interference dip in the broad level. At higher fields the interference eventually gives rise to two split components. The results are in good agreement with a nonperturbative theory, summarized in this letter.We have observed the effect of electric fields on the 5d9p ${}^{3}$${P}_{1}$\ifmmode^\circ\else\textdegree\fi{} barium resonance above the first ionization threshold. This relatively broad autoionizing level is nearly degenerate with a much narrower level of opposite parity. At moderate fields the sharp level produces an interference dip in the broad level. At higher fields the interference eventually gives rise to two split components. The results are in good agreement with a nonperturbative theory, summarized in this letter.

Physical Review LettersJul 8, 198536 citations

We have measured the relative population in the two

{\mathit{m}}_{\mathit{j}}

states of barium 6

{\mathit{p}}_{1/2}

ions produced by the autoionization of (6

{\mathit{p}}_{3/2}

{)}_{\mathit{J}=\mathit{M}\mathit{J}}

=3 states by detecting the helicity of the emitted fluorescence. These populations can be related to the relative branching ratio into the 6

{\mathit{p}}_{1/2}

\ensuremath{\epsilon}

{\mathit{d}}_{5/2}

and 6

{\mathit{p}}_{1/2}

\ensuremath{\epsilon}

{\mathit{g}}_{7/2}

continuum channels. Rydberg states with n=16--23 have similar branching ratios, producing approximately six times as much 6

{\mathit{p}}_{1/2}

\ensuremath{\epsilon}

{\mathit{d}}_{5/2}

population as 6

{\mathit{p}}_{1/2}

\ensuremath{\epsilon}

{\mathit{g}}_{7/2}

population.

We report the effects of static electric fields on the doubly excited

6{p}_{\frac{1}{2}}\mathrm{nl}

states of barium in the region

{n}^{*}=12

. Using a three-step laser excitation scheme we have measured the electric-field dependence of the positions and autoionization widths of the $6{p}_{\frac{1}{2}}\ensuremath{-}17s,16p,15d,12l (l=4\ensuremath{-}10),12f, \mathrm{and} 16s$ states at field values of up to 4.92 kV/cm. The photoexcitation spectra of the autoionizing states exhibit interference effects which are well understood and provide a better understanding of the character of these states in electric fields. The systematic study of the spectra and positions allows us to explain the field dependence of the autoionization widths in terms of electric-field mixing of the discrete portions of the auoionizing states. The relationship of these effects to dielectronic recombination rates of ions and electrons in plasma microfields is discussed.

We have measured the lifetimes of

^{1}P^{e}

(n=9--12)

doubly excited states in static electric fields

(1--6\phantom{\rule{0.3em}{0ex}}\mathrm{kV}∕\mathrm{cm})

by observing the decay of the fluorescence signal as a function of time. The effects of the field on these helium states below the second ionization threshold are twofold: their excitation becomes possible due to the Stark mixing with the optically allowed

^{1}P^{o}

series, and their lifetime is strongly modified by the opening of the autoionization channel, not accessible in zero field. Although the electric field represents only a tiny perturbation of the atomic potential, a substantial shortening of the lifetimes below

100\phantom{\rule{0.3em}{0ex}}\mathrm{ps}

is observed. This is the simplest quantum system where the ratio of autoionization to fluorescence decay probability can be effectively controlled by an electric field of moderate strength.

We have observed the effect of electric fields on the 5d9p

{}^{3}

{P}_{1}

\ifmmode^\circ\else\textdegree\fi{} barium resonance above the first ionization threshold. This relatively broad autoionizing level is nearly degenerate with a much narrower level of opposite parity. At moderate fields the sharp level produces an interference dip in the broad level. At higher fields the interference eventually gives rise to two split components. The results are in good agreement with a nonperturbative theory, summarized in this letter.