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Physical Review A

Multipulse laser spectroscopy of p- bartHe+ : Measurement and controlof the metastable state populations

Vladimir Leonardovich Derbov, Leonid A. Melnikov, И. М. Уманский, Sergue Il'ich Vinitsky

Published May 1, 1997• 11 citations
Publisher

Abstract

Numerical study of the kinetics in metastable antiprotonic helium molecules driven by a sequence of laser \ensuremath{\pi} pulses resonant to the adjacent transitions is carried out. The phenomena taking place are shown to be useful for checking the mechanisms of the depopulation of high-n states, for measuring the populations of the individual energy levels, and for slowing down the decay by means of \ensuremath{\pi}-pulse-induced inversion.

DOI
10.1103/physreva.55.3394

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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE•May 9, 2001•0 citations
Numerical study of the kinetics in metastable antiprotonic helium molecules driven by a sequence of laser \ensuremath{\pi} pulses resonant to the adjacent transitions is carried out. The phenomena taking place are shown to be useful for checking the mechanisms of the depopulation of high-n states, for measuring the populations of the individual energy levels, and for slowing down the decay by means of \ensuremath{\pi}-pulse-induced inversion.
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.
Laser resonance transitions between normally metastable states of antiprotonic helium atoms were observed making use of state dependent quenching effects caused by small admixtures of H2{\mathrm{H}}_{2}H2​ molecules. By selectively shortening the lifetimes of states with higher principal quantum number nnn as compared to those of lower nnn, this method for the first time provides access to all initially populated metastable states of p‾He+\overline{p}{\mathrm{He}}^{+}p​He+ atoms. This was demonstrated by observing the transitions $(n,l)\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}(38,l)\ensuremath{\rightarrow}(39,l+1)$, l=35,36,37l\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}35,36,37l=35,36,37 and $(n,l)\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}(37,l)\ensuremath{\rightarrow}(38,l+1)$, l=34,35,36l\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}34,35,36l=34,35,36.
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.
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.