Increase of the positronium lifetime under high-frequency, intense laser fields

Lima, F. M. S.; Amato, M. A.; Nunes, O. A. C.; Fonseca, A. L. A.; Silva, E F da

doi:10.1088/0953-4075/42/5/055601

Cited by 10 publications

(12 citation statements)

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“…Higher order annihilation processes can occur for states with l > 0 but are strongly suppressed [4] and in practice direct Ps annihilation occurs only from the ground 1 1 S 0 and 1 3 S 1 , and metastable 2 1 S 0 and 2 3 S 1 levels. The inhibition of Ps annihilation in states with l > 0 is the basis for several proposed schemes to manipulate annihilation rates using resonant and nonresonant laser fields [5][6][7][8][9][10][11]. More complex strategies have also been suggested [12,13], although these have also not yet been experimentally demonstrated.…”

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confidence: 99%

Controlling Positronium Annihilation with Electric Fields

et al. 2015

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We show that the annihilation dynamics of excited positronium (Ps) atoms can be controlled using parallel electric and magnetic fields. To achieve this, Ps atoms were optically excited to n ¼ 2 sublevels in fields that were adjusted to control the amount of short-lived and long-lived character of the resulting mixed states. Inclusion of the former offers a practical approach to detection via annihilation radiation, whereas the increased lifetimes due to the latter can be exploited to optimize resonance-enhanced two-photon excitation processes (e.g., 1 3 S → 2 3 P → nS=nD), either by minimizing losses through intermediate state decay, or by making it possible to separate the excitation laser pulses in time. In addition, photoexcitation of mixed states with a 2 3 S 1 component represents an efficient route to producing long-lived pure 2 3 S 1 atoms via single-photon excitation. DOI: 10.1103/PhysRevLett.115.183401 PACS numbers: 36.10.Dr, 78.70.Bj Positronium (Ps) is an atomic system composed of an electron bound to a positron and has several unique properties, the most striking of which are its low mass (M Ps ¼ 2m e ) and the fact that it can decay through various annihilation pathways [1]. Electron-positron annihilation requires overlap of the particle wave functions [2] and in Ps is therefore dependent on the square of the radial wave function at the origin. This is zero for states with l > 0 [3]. Higher order annihilation processes can occur for states with l > 0 but are strongly suppressed [4] and in practice direct Ps annihilation occurs only from the ground 1 1 S 0 and 1 3 S 1 , and metastable 2 1 S 0 and 2 3 S 1 levels. The inhibition of Ps annihilation in states with l > 0 is the basis for several proposed schemes to manipulate annihilation rates using resonant and nonresonant laser fields [5][6][7][8][9][10][11]. More complex strategies have also been suggested [12,13], although these have also not yet been experimentally demonstrated.The radiative decay and annihilation time scales in the n ¼ 2 manifold in Ps span an enormous range: The 2 1 S 0 level is radiatively metastable, fluorescing on a time scale of ≃0.24 s [3], but annihilating in 1 ns; conversely the 2 3 P 0;1;2 levels decay by fluorescence to the 1 3 S 1 state in 3.19 ns, but their annihilation lifetimes exceed 100 μs [4]. The 2 3 S 1 level is also metastable and fluoresces in ≃0.24 s, but has an annihilation lifetime of ∼1.14 μs [1]. It is the disparate properties of these states that make the approach described here to manipulating decay rates particularly effective.We report the results of experiments in which Ps annihilation rates in a weak magnetic field are manipulated using parallel electric fields. This combination of fields permits control over the spin multiplicity and orbital angular momentum character of the n ¼ 2 sublevels accessible by single-photon excitation from the 1 3 S 1 ground state. By increasing the 2 1 P character of mixed states in the fields, radiative decay to the short-lived singlet ground state (1 1 S 0 ) can be...

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Controlling Positronium Annihilation with Electric Fields

et al. 2015

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“…For linear polarisation, this was carried out in refs. [33] and [34]. Both treatments obtained similar results, using somewhat different approximate wavefunctions.…”

Section: Inhibition Of Annihilationmentioning

confidence: 67%

“…Also, both evaluated the lifetimes at small quiver amplitudes, at most about a Bohr radius. As shown in our Appendix, much [33] and [34] for linearly polarised laser fields. Table 3 gives functions fitted to our data.…”

Section: Inhibition Of Annihilationmentioning

confidence: 79%

“…For the para-Ps ( 1 S 0 ) and ortho-Ps ( 3 S 1 ) ground states, annihilation via electron-positron collisions forms, at low energy, dominantly two or three γ -photons, respectively [32]. Standard approximate results from quantum electrodynamics [34] give the annihilation rates as…”

Section: Inhibition Of Annihilationmentioning

confidence: 99%

“…In previous work, the annihilation lifetimes for para-Ps (spins antiparallel) and ortho-Ps (spins parallel) have been evaluated for field-free conditions [28]. Effects on annihilation lifetimes have also been considered, mostly in qualitative fashion, for external fields ranging from weak to strong [29][30][31][32][33][34]. Superintense laser fields have been treated in two studies using HFFT [33,34], but we find the calculations made of annihilation lifetimes pertain to quiver amplitudes much too small to satisfy the HFFT validity criteria.…”

Section: Introductionmentioning

confidence: 99%

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Positronium in superintense high-frequency laser fields

Herschbach

2013

Molecular Physics

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The distortion induced by a superintense high-frequency laser field inhibits both ionisation of a ground state positronium atom (Ps) to emit e − and e + and annihilation to decay into γ -rays. We apply high-frequency Floquet theory (HFFT) to evaluate the half-life for both ionisation and annihilation of Ps in either a linearly or circularly polarised field, over quiver amplitudes (governed by the ratio of laser field strength to the square of the oscillation frequency) extending to ∼100 au and beyond. We also consider the HFFT validity criteria, which set upper and lower bounds on the laser frequency, and present a generally applicable plot that facilitates determining the optimal quiver amplitude and laser intensity. For currently available lasers that satisfy the validity criteria, the laser-induced lifetimes become far longer than field-free values, but the ionisation lifetime is 10 5 -fold or more shorter than the annihilation lifetime for para-Ps (spins antiparallel) and 10 8 -fold shorter than that for ortho-Ps (spins parallel).

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