On the formation of excited state positronium in vacuum by positron impact on untreated surfaces

Day, D J; Charlton, M.; Laricchia, G.

doi:10.1088/0953-4075/34/18/301

Cited by 14 publications

(13 citation statements)

References 22 publications

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“…Further, the present theoretical estimates, in absence of any other results , could provide some guidelines to the future experiments involving individual excited Ps states , the latter being already feasible for the Ps formation process [ 5 ] . The excited states of the H atom on the other hand, are expected to be less important than those of the Ps in the − H ion formation.…”

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confidence: 76%

Formation of negative hydrogen ion in positronium-hydrogen collisions

Roy¹,

Sinha²

2008

Eur. Phys. J. D

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confidence: 76%

Formation of negative hydrogen ion in positronium-hydrogen collisions

Roy¹,

Sinha²

2008

Eur. Phys. J. D

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“…Conversely, φ Ps (n = 2) is always positive, and excited state Ps atoms can only be formed in metals by epithermal positrons. This process has been observed for several metals [259][260][261][262] and facilitated the first observation of Ps Lyman α radiation [263] as well as microwave spectroscopy of n = 2 transitions [264][265][266]. However, this method of producing n = 2 atoms is generally very inefficient, and is not a viable substitute for laser excitation [139].…”

Section: Ps Productionmentioning

confidence: 99%

“…One of the limiting factors in previous experiments was that n = 2 atoms had to be produced through positron collisions with certain surfaces [262,263,608], which is very inefficient (on the order of 0.1%), and thus imposed statistical limitations. Much more efficient production of n = 2 atoms can be accomplished by laser excitation [139].…”

Section: Precision Spectroscopymentioning

confidence: 99%

Experimental progress in positronium laser physics

2018

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Abstract. The field of experimental positronium physics has advanced significantly in the last few decades, with new areas of research driven by the development of techniques for trapping and manipulating positrons using Surko-type buffer gas traps. Large numbers of positrons (typically ≥10 6 ) accumulated in such a device may be ejected all at once, so as to generate an intense pulse. Standard bunching techniques can produce pulses with ns (mm) temporal (spatial) beam profiles. These pulses can be converted into a dilute Ps gas in vacuum with densities on the order of 10 7 cm −3 which can be probed by standard ns pulsed laser systems. This allows for the efficient production of excited Ps states, including long-lived Rydberg states, which in turn facilitates numerous experimental programs, such as precision optical and microwave spectroscopy of Ps, the application of Stark deceleration methods to guide, decelerate and focus Rydberg Ps beams, and studies of the interactions of such beams with other atomic and molecular species. These methods are also applicable to antihydrogen production and spectroscopic studies of energy levels and resonances in positronium ions and molecules. A summary of recent progress in this area will be given, with the objective of providing an overview of the field as it currently exists, and a brief discussion of some future directions.

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“…Previously demonstrated methods for the preparation of 2 3 S 1 states of Ps involve two-photon excitation of ground state atoms [35][36][37], or positron impact on untreated surfaces [38][39][40][41]. However, if appropriate mixed states are extracted into an electric-field-free region then pure 2 3 S 1 atoms can be obtained.…”

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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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On the formation of excited state positronium in vacuum by positron impact on untreated surfaces

Cited by 14 publications

References 22 publications

Formation of negative hydrogen ion in positronium-hydrogen collisions

Formation of negative hydrogen ion in positronium-hydrogen collisions

Experimental progress in positronium laser physics

Controlling Positronium Annihilation with Electric Fields

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