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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

Numerical modeling of some peculiarities of multipulse excitation of antiprotonic helium

Vladimir Leonardovich Derbov, Leonid A. Melnikov, Natalia I. Teper, И. М. Уманский

Published Mar 20, 2000• 0 citations
Publisher

Abstract

We report the results of numerical modeling of the coherent laser multi-pulse technique, proposed in our earlier papers to measure the population of the metastable states of antiprotonic helium and to control the decay kinetics in the adjacent transition chains. It is demonstrated that a sequence of properly chosen (pi) -pulses may result in a sequence of annihilation spikes whose amplitudes are nearly proportional to the populations of individual metastable states. The limitations related to the pulse duration and delay are studied as well as the role of the lifetime of the short-lived final state.

DOI
10.1117/12.380130

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Journal of Optics B Quantum and Semiclassical Optics•Aug 1, 2001•0 citations
We report the results of numerical modeling of the coherent laser multi-pulse technique, proposed in our earlier papers to measure the population of the metastable states of antiprotonic helium and to control the decay kinetics in the adjacent transition chains. It is demonstrated that a sequence of properly chosen (pi) -pulses may result in a sequence of annihilation spikes whose amplitudes are nearly proportional to the populations of individual metastable states. The limitations related to the pulse duration and delay are studied as well as the role of the lifetime of the short-lived final state.
We report the results of numerical modeling of the coherent action of a single short laser pulse on a multilevel quantum system of metastable and short-lived states of antiprotonic helium. Increasing the pulse intensity we observed more new states getting involved into the coherent interaction, their populations being affected by the pulse. Examples of intensity-dependent dynamics of the metastable states populations are considered. Extraction of spectroscopic information about the states of antiprotonic helium from the experiments with fixed-frequency variable-intensity laser pulses is discussed.
The time evolution of the state populations in the $v\ensuremath{\equiv}n\ensuremath{-}\ensuremath{\ell}\ensuremath{-}1=2$ and 3 metastable cascades of antiprotonic helium (p‾4He+{\overline{p}}^{4}{\mathrm{He}}^{+}p​4He+) atoms were studied using laser spectroscopy. The antiprotonic states $(n,\ensuremath{\ell})=(39,35)$, (40,36), and (41,37) in the v=3v=3v=3 cascade were estimated to initially contain, respectively, $(0.28\ifmmode\pm\else\textpm\fi{}0.04)%$, $(0.06\ifmmode\pm\else\textpm\fi{}0.02)%$, and $(0.02\ifmmode\pm\else\textpm\fi{}0.01)%$ of the antiprotons stopped in the helium target, while the corresponding values for states (37,34)(37,34)(37,34), (38,35)(38,35)(38,35), and (39,36)(39,36)(39,36) in the v=2v=2v=2 cascade were $(0.21\ifmmode\pm\else\textpm\fi{}0.04)%$, $(0.49\ifmmode\pm\else\textpm\fi{}0.07)%$, and $(0.19\ifmmode\pm\else\textpm\fi{}0.07)%$. The shortening of the state lifetimes due to collisions between p‾He+\overline{p}{\mathrm{He}}^{+}p​He+ and helium atoms was studied. As the atomic density of the target was increased from $\ensuremath{\rho}=2\ifmmode\times\else\texttimes\fi{}{10}^{20}$ to $2\ifmmode\times\else\texttimes\fi{}{10}^{21}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$, the lifetime of state (37,34)(37,34)(37,34) decreased by an order of magnitude, whereas the higher states (38,35)(38,35)(38,35) and (39,35)(39,35)(39,35) were relatively unaffected. Between densities $\ensuremath{\rho}=6\ifmmode\times\else\texttimes\fi{}{10}^{20}$ and $2\ifmmode\times\else\texttimes\fi{}{10}^{22}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$, a short-lived component with a time constant $\ensuremath{\tau}\ensuremath{\sim}0.2\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{s}$ appeared at early times in the delayed annihilation time spectrum of p‾He+\overline{p}{\mathrm{He}}^{+}p​He+, while the total fraction of long-lived antiprotons decreased from 3.0 to 2.52.5%2.5. These effects were caused by the lifetime-shortening of specific p‾He+\overline{p}{\mathrm{He}}^{+}p​He+ states such as (37,34)(37,34)(37,34).
Laser studies of metastable antiprotonic helium atoms, which we recently initiated by observing a sharp increase of the antiproton annihilation rate induced by laser-stimulated resonant transitions, have been extended. With a single laser tuned to the resonance already found at 597.26 nm, we have now established the time dependence of the upper state population. With two lasers ignited at variable time separation, we also studied the feeding of the upper state from higher atomic levels. The initial populations and level lifetimes of excited exotic atoms were determined.