Abstract
We investigate experimentally the possibility of enhancing the production of $2^3S$ positronium atoms by driving the $1^3S$-$3^3P$ and $3^3P$-$2^3S$ transitions, overcoming the natural branching ratio limitation of spontaneous decay from $3^3P$ to $2^3S$. The decay of $3^3P$ positronium atoms towards the $2^3S$ level has been effciently stimulated by a 1312.2nm broadband IR laser pulse. The dependence of the stimulating transition efficiency on the intensity of the IR pulse has been measured to find the optimal enhancement conditions. A maximum relative increase of $ \times (3.1 \pm 1.0) $ in the $2^3S$ production efficiency, with respect to the case where only spontaneous decay is present, was obtained.
Highlights
Positronium (Ps) is the neutral matter-antimatter bound state of an electron (e−) and a positron (e+)
A set of reference spontaneous 2 3S Ps production measurements was acquired on the detuned optical parametric generation (OPG) set point (T2) to measure the S(t ) = [Aoff (t ) − AUV(t )]/Aoff (t ) parameter in the absence of stimulated emission in the conditions selected for the following experiments
The peak of 2 3S annihilations on the chamber walls is more evident in the on-resonance (T1) measurement than in the detuned (T2) measurement, where it is lower and smeared to longer times, in agreement with a reduced 2 3S production efficiency and longer atoms’ traveled distances, because of the Doppler selection operated by the detuned UV beam that selects atoms traveling longer trajectories
Summary
Positronium (Ps) is the neutral matter-antimatter bound state of an electron (e−) and a positron (e+). The 2 3S level has an extended lifetime of 1142 ns in vacuum This is due to its optical metastability: single-photon radiative decays to 1 3S are prohibited by the electric dipole selection rules, and the reduced overlap between the positron and the electron wave functions increases its annihilation lifetime by a factor of 8 [4]. On top of its high-precision spectroscopy applications, 2 3S Ps is one of the few notable candidate systems being considered for measuring the gravitational interaction between matter and antimatter [5], together with Ps in longlived Rydberg states [6,7], antihydrogen [8–10], and muonium [11]. An intense source of polarized 2 3S atoms has been recently shown to be of extreme usefulness to achieve Bose-Einstein condensation of Ps [13]
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