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Physical Review Letters

Detection of Singly Stimulated Two-Photon Emission from Metastable Deuterium Atoms

P. Bräunlich, P. Lambropoulos

Published Jul 20, 1970• 31 citations
Publisher

Abstract

The observation of singly stimulated two-photon emission from metastable deuterium atoms is reported. A collimated beam of metastables is produced by charge exchange between cesium vapor and 5-keV deuterons. A pulsed Nd-glass laser is used for the stimulation. The generated 1373-\AA{} photons are detected at the exit slit of a spectrometer. Single-photon counting techniques are employed. The results obtained are in good agreement with theoretical calculations.

DOI
10.1103/physrevlett.25.135

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The observation of singly stimulated two-photon emission from metastable deuterium atoms is reported. A collimated beam of metastables is produced by charge exchange between cesium vapor and 5-keV deuterons. A pulsed Nd-glass laser is used for the stimulation. The generated 1373-\AA{} photons are detected at the exit slit of a spectrometer. Single-photon counting techniques are employed. The results obtained are in good agreement with theoretical calculations.
The authors report the observation of the 1S-2S two-photon transition in atomic hydrogen in an atomic beam, excited by light from a narrow-band continuous-wave laser. The excitation takes place in a collision-free environment and detection of the resonance is carried out by Stark-quenching the metastable atoms some distance from the interaction region. This approach removes the limitations of cell excitation employed in previous experiments with continuous-wave lasers, and should allow the full precision of modern tunable laser techniques to be applied to the 1S-2S transition. It also gives a new method for producing a collimated beam of metastable atoms which has particular applications to a variety of future experiments with cold hydrogen.
A 1-keV metastable atomic deuterium [D(2S)] beam of density about 104 atoms cm-3 has been produced by charge-exchange, in caesium vapour, of deuterons extracted from a radio-frequency ion source. The linear and circular polarisation correlation of the two photons emitted spontaneously by metastable atomic deuterium in a true second order radiative process have been measured for the first time. While the circular polarisation results confirm the conservation of angular momentum along the common axis of detection, the correlation in linear polarisation has been applied in a test of Bell’s Inequality which allows a quantitative distinction to be made between the predictions of Quantum Mechanics and local realistic ("hidden variable") theories. The results are in agreement with Quantum Mechanics and violate Bell’s Inequality by almost two standard deviations.
We report a novel method of determining the coherence length of photons produced in the two-photon decay of metastable atomic deuterium by observing the depolarization of the photons in what is essentially a true single-photon interference experiment. In the Stirling source two photons propagating in the ±z directions are detected in coincidence. The degree of polarization of the radiation emerging from a multiwave plate placed on one side of the source as a function of the optical path difference 6 introduced by the multiwave plate between the orthogonally polarized components is determined by measuring the Stokes' parameters. The results confirm the dependence of the depolarizing effect of the multiwave plate on 6, agree with the quantum mechanical predictions and allow a measurement to be made of the coherence length of single photons of the two-photon pair. \nWe also report the results t>f an experiment which, for the first time, demonstrates the action of an achromatic half-wave plate on the polarization state of the two-photon radiation emitted by atomic deuterium in the metastable 2Sv, state The results agree with the quantum mechanical predictions and confirm the hypothesis of Breit and Teller that the fine and hyperfine interaction play no role in the emission process.
Two-photon-resonant, three-photon ionization of atomic hydrogen and deuterium is performed at 243 nm, and the ions are detected by time-of-flight mass spectrometry. The power dependence of the 1S-2S two-photon excitation and one-photon ionization of 2S hydrogen and deuterium are determined. The ionization step saturates at 4 x 10(6) W/cm(2). The two-photon step-power dependence varies with laser linewidth, with saturation occurring between 1 x 10(7) and 3 x 10(7) W/cm(2). The extraction electric field in the mass spectrometer does not affect the 2S excitation. Strong signals are recorded at atomic concentrations of 10(5) atoms/cm(3). Nonresonant ionization of background gases producing H(+) and D(+) is minimized.