Detection of naturally occurring xenon in air by magnetically induced depolarization of coherent microwave Rayleigh scattering from resonance-enhanced multiphoton ionization

The detection of naturally occurring xenon (129Xe) in ambient air was demonstrated using the magnetically induced depolarization of Radar REMPI (coherent microwave Rayleigh scattering from Resonance-Enhanced Multi-Photon Ionization). The study employs a 2 + 1 REMPI scheme, where two photons (222–226 nm) from a tunable narrow-linewidth laser excite a xenon atom to resonant intermediate states (6p′[1/2], 6p′[3/2], 7p[1/2], 7p[3/2], and 7p[5/2]), followed by the absorption of a third photon to ionize the excited atom. Magnetically induced depolarization of microwave scattering was applied to enhance the sensitivity by a factor of ∼3. The time-dependent quantum perturbation theory was used to calculate the multiphoton absorption cross section of xenon near 222–226 nm region, which qualitatively agrees with the experimental results. This study enables the identification and quantification of naturally occurring xenon in air, demonstrating detection sensitivity in the tens of parts per billion (ppb) range.