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Physical Review A

Change of the annihilation rate of Ps in a resonant laser

Marvin H. Mittleman

Published Apr 1, 1986• 15 citations
Publisher

Abstract

The annihilation rate of Ps is proportional to the square of the wave function at the origin. This can be affected by exposure of the atom to a resonant laser. The result depends upon whether the excited state is an S or a P state and whether it is singlet or triplet. An alteration of the decay rate by as much as a factor of 2 is possible.

DOI
10.1103/physreva.33.2840

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The annihilation rate of Ps is proportional to the square of the wave function at the origin. This can be affected by exposure of the atom to a resonant laser. The result depends upon whether the excited state is an S or a P state and whether it is singlet or triplet. An alteration of the decay rate by as much as a factor of 2 is possible.
We report a measurement of the annihilation decay rate of positronium (Ps) atoms, . Ground state atoms optically excited to radiatively metastable states were quenched via Stark mixing by the application of a time-delayed electric field. Rapid radiative decay of the Stark mixed states to the ground state, followed by self-annihilation, was observed via the annihilation radiation time spectrum, and used to determine the number of excited state atoms remaining at different times, and hence the decay rate. We obtain , in broad agreement with the Zeeman-shifted theoretical value of .
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.
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 fluorescence decay rate of 2 P J 3 positronium (Ps) atoms [ Γ fl ] has been experimentally determined using a Stark-mixing technique. Ground-state Ps atoms were optically excited in an electric field to states containing both 2 P J 3 and 2 3 S 1 components. The relative state populations were controlled via an applied mixing electric field, and a larger, pulsed, electric field was used to induce rapid quenching of the system after a fixed time delay. The dependence of the quenching signal on the mixing field strength was used to determine the relative and populations of the mixed states, whose decay rates are determined by the intrinsic self-annihilation and fluorescence decay rates. The measurements were compared to a trajectory simulation and Stark-mixing model, using the fluorescence decay rate as a free parameter. By finding the best agreement between the data and simulations we obtain Γ fl = 299 ± 25 µ s − 1 , which is consistent with the mean theoretical value of 313.343 ± 0.003 µ s − 1 . Published by the American Physical Society 2024
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 para-positronium atom from two states participating in stimulated optical transitions excited by a laser. It is shown that a non- exponential 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 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 1S state.