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NASA conference publication

Optically excited states in positronium

Richard H. Howell, Klaus P. Ziock, F. Magnotta, CHARLES D. DERMER, R. Failor, K. M. Jones

Published Jan 1, 1990• 0 citations
OpenAlex

Abstract

We report optical excitation of the 1{sup 3}S-2{sup 3}P transition in positronium, and a second excitation from n=2 to higher n states. The experiment used light from two pulsed dye lasers. Changes in the positronium annihilation rate during and after the laser pulse were used to deduce the excited state populations. We found that we could saturate the n=2 level and excite a substantial fraction of n=2 positronium to higher levels. Preliminary spectroscopic measurements were performed on n=14 and n=15 positronium. 14 refs., 7 figs.

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•Aug 1, 1988•0 citations
We report optical excitation of the 1{sup 3}S-2{sup 3}P transition in positronium, and a second excitation from n=2 to higher n states. The experiment used light from two pulsed dye lasers. Changes in the positronium annihilation rate during and after the laser pulse were used to deduce the excited state populations. We found that we could saturate the n=2 level and excite a substantial fraction of n=2 positronium to higher levels. Preliminary spectroscopic measurements were performed on n=14 and n=15 positronium. 14 refs., 7 figs.
The authors report optical saturation of the 1 3 S-2 3 P transition in positronium using ultraviolet light from a frequency-doubled, pulsed dye laser. The increase in ground-state annihilation radiation due to magnetic triplet-singlet mixing in the excited state is used to monitor the transition. From the variation of the annihilation rate as a function of magnetic field, laser power, wavelength and polarisation, the authors verify that the transition is optically saturated, in agreement with model calculations of the system.
The $1^{3}S_{1}\ensuremath{\rightarrow}2^{3}S_{1}$ transition in positronium has been observed using two-photon Doppler-free excitation. Transitions were induced by a pulsed dye laser, and detected by photoionization of the 23S12^{3}S_{1}23S1​ state. The resonance signal has a linewidth of 1.5 GHz and a signal-to-noise ratio of 20:1. The frequency agrees with theory to 0.5 GHz. The resonance signal has an amplitude proportional to the square of the laser intensity and displays the expected Stark shift to higher frequency under an applied electric field.
The problem of the interaction of a positronium atom with the field of optical and annihilation photons is considered. The solution obtained for the occupation numbers is used to study kinetics of the annihilation decay of a para-positronium atom from two (for example, 1 S and 2 P ) states participating in stimulated optical transitions excited by a laser. It is shown that a nonexponential time dependence of the occupation numbers is observed under the conditions of a nonlinear coherent interaction of a positronium atom with the field of optical and annihilation photons, and that in some cases there is a possibility of appearance of a long-lived state of a positronium atom with a lifetime hundreds of times longer than the lifetime of a positronium atom in the 1 S state.
We report experiments in which positronium (Ps) atoms are produced in the 23S12\phantom{\rule{0.16em}{0ex}}^{3}S_{1}23S1​ level by single-photon excitation from the ground state. To accomplish this, Stark-mixed n=2n=2n=2 states were optically excited in electric fields. By adiabatically switching off the electric field after laser excitation, some of the mixed states evolved into pure 23S12\phantom{\rule{0.16em}{0ex}}^{3}S_{1}23S1​ levels, whose presence was detected via the time dependence of their annihilation $\ensuremath{\gamma}$ radiation. The observed $\ensuremath{\approx}4%$ production efficiency relative to that of Rydberg Ps states is consistent with a Monte Carlo simulation that takes into account the rate at which the electric fields were switched off.
The 33P state of positronium is an intermediate level suitable for producing long-lived positronium states. On one hand, it can be used in a two-step laser excitation scheme from the ground state to Rydberg levels. On the other hand, excitation of positronium to 33P level is a simple pathway for producing metastable 23S positronium atoms by spontaneous radiactive decay. In this work, experiments showing the production of such long-lived levels, using the 33P state as intermediate state, are presented. The characteristics of the two long-lived levels, in view of experiments of deflectometry/interferometry with positronium, are discussed.
Our demonstration of multiple-photon resonant cycling between the 1/sup 3/S and 2/sup 3/P states of ortho-Positronium (oPs) makes possible the production of cold positronium (Ps) through the technique of laser cooling. A simplified analysis of magnetic mixing in excited-state Ps is given. This effect is important both as a diagnostic of resonant cycling and Ps cooling. The significance of cold Ps in fine structure measurements and the formation of a Bose-Einstein condensate is discussed. 13 refs., 3 figs.