Observation of Positronium Specular Reflection from LiF

Weber, Marc H.; Tang, S. Y.; Berko, S.; Brown, B. L.; Canter, K. F.; Lynn, Kelvin G.; Mills, A. P.; Roellig, L. O.; Viescas, A. J.

doi:10.1103/physrevlett.61.2542

Cited by 56 publications

(33 citation statements)

References 7 publications

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“…36) [120,559]. Energy tunable Ps beams can be made by passing a positron beam through a gas cell [85,231,560,561], or by glancing angle positron scattering [562]. These methods can generate beams in the energy ranges of approximately 5-500 eV and 10-100 eV, respectively.…”

Section: Ps − 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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Section: Ps − Spectroscopymentioning

confidence: 99%

Experimental progress in positronium laser physics

2018

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“…We shall discuss data obtained from two p-Si samples that were cleaned in slightly different ways. As described in ref [35], the first p-Si(100) target had dimensions 10×10×0.34 mm 3 with a resistivity we measured to be 2.7 Ωcm at 300K, corresponding to (5.2±0.2)×10 15 Boron atoms cm -3 . The sample surface was prepared by dipping in 100% ethanol, followed by dipping in ~2-4% HF for ~1 minute to remove the surface oxide, as evidenced by the surface becoming hydrophobic.…”

Section: Sample Preparationmentioning

confidence: 99%

“…The first observation of Ps by Deutsch in 1951 [14] used fast positrons emitted by a 22 Na source interacting with N 2 and NO gases. A similar technique using a moderated positron beam and a gas cell is still used today to produce tunable Ps beams for atomic physics scattering measurements [7,15].…”

Section: Introductionmentioning

confidence: 99%

Positronium formation via excitonlike states on Si and Ge surfaces

et al. 2011

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Recent experiments combining lifetime and laser spectroscopy of positronium (Ps) show that these atoms are emitted from p-Si(100) at a rate that depends on the sample temperature, suggesting a thermal activation process, but with an energy that does not, precluding direct thermal activation as the emission mechanism. Moreover, the amount of Ps emitted is substantially increased if the target is irradiated with 532 nm laser light just prior to the implantation of the positrons. Our interpretation of these data was that the Ps was emitted via an exciton-like positron-electron surface state, not dissimilar to an electronic surface exciton observed on Si in two-photon photoemission measurements. The hypothesis that this state may be populated by electrons from one of the occupied electronic surface states, either thermally or by laser excitation, is consistent with our observations and suggests that one should expect a high Ps yield at room temperature from an n-doped Si(100) sample, since in this case the same surface states will already be occupied. Here we present data obtained with an n-Si(100) target that supports our model, and also reveals the unexpected result that the kinetic energy of Ps emitted from this material actually decreases when it is heated, an effect we attribute to shifts in the surface energy levels due to the presence of a high density of thermally generated electrons. We show data obtained with a Ge(100) sample that corroborate the idea that the effects we observe are related to surface electron states, and hence should occur for any indirect band gap semiconductor with dangling bond states. Our model is further confirmed by the observation that the Ps yield from p-Si depends linearly on the surface density of the implanted positrons due to the effects of electron-hole pairs created as the positrons slow down.

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“…This technique has been used for the observation of Ps specular reflection from a LiF surface [26] and the measurement of Ps-gas scattering cross sections in the energy range below 100eV [27]. Formation of Ps beams with a kinetic energy from 10 to 500eV have also been tried by partial transmission of keV-energy positrons through 5nm carbon film [28].…”

Section: Ps − Photodetachmentmentioning

confidence: 99%