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Measurement of Ultrafast Vibrational Coherences in Polyatomic Radical Cations with Strong-Field Adiabatic Ionization
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Positronium hyperfine interval measured via saturated absorption spectroscopy.

D B Cassidy1, T H Hisakado, H W K Tom

  • 1Department of Physics and Astronomy, University of California, Riverside, 92521-0413, USA.

Physical Review Letters
|September 26, 2012
PubMed
Summary

Scientists precisely measured the positronium (Ps) Lyman-α transition using Doppler-free spectroscopy. This optical method yielded the first measurement of the Ps hyperfine interval, E(hfs), at 198.4 ± 4.2 GHz.

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Area of Science:

  • Atomic Physics
  • Quantum Electrodynamics (QED)
  • Spectroscopy

Background:

  • Positronium (Ps) is a fundamental leptonic atom composed of an electron and a positron.
  • Precision measurements of Ps properties test fundamental theories like QED.
  • Discrepancies exist between theoretical predictions and experimental results for Ps properties.

Purpose of the Study:

  • To perform Doppler-free measurements of the positronium Lyman-α transition.
  • To achieve the first optical measurement of the positronium hyperfine interval (E(hfs)).
  • To explore methods for higher precision measurements to resolve theoretical-experimental discrepancies.

Main Methods:

  • Saturated absorption spectroscopy was employed for Doppler-free measurements.
  • Observation of a Lamb dip and a crossover resonance.
  • Analysis of the wavelength difference between the Lamb dip and crossover resonance to determine E(hfs).

Main Results:

  • The positronium Lyman-α transition was measured with high precision.
  • A Lamb dip was observed at λ(L) = 243.0218 ± 0.0005 nm.
  • A crossover resonance was observed at λ(C) = 243.0035 ± 0.0005 nm, yielding E(hfs) = 198.4 ± 4.2 GHz.

Conclusions:

  • This study presents the first optical measurement of the positronium hyperfine interval.
  • The results provide a new avenue for testing QED predictions.
  • Methodological improvements are discussed for achieving ppm-level precision in future experiments.