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Journal of Physics B Atomic Molecular and Optical Physics

Intensity-dependent polarization correlations in the field-free 6S to 7S to 15P two-photon transition of caesium

Nick Schlumpf, V. L. Telegdi, Antoine Weis, Dimitrios Zevgolis, Luming Zhao, John A. Hoffnagle

Published Jun 14, 1991• 0 citations
Publisher

Abstract

The authors investigated the resonant M1-E1 two-photon transition (6S12/ to 7S12/ to 15P32/) in caesium using counterpropagating single-mode laser beams in a thermionic diode. They measured circular polarization correlations, i.e. the dependence of the two-photon transition rate on the relative helicities of the two circularly polarized beams. The results depend strongly on the intensity of the laser driving the 7S to 15P transition and are in good agreement with theoretical predictions from a rate equation treatment taking collisional population redistributions among the 15p32/ states into account. The implications of the results for a field-free parity violation experiment are discussed.

DOI
10.1088/0953-4075/24/11/011

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Journal de Physique Lettres•Jan 1, 1975•23 citations
The authors investigated the resonant M1-E1 two-photon transition (6S12/ to 7S12/ to 15P32/) in caesium using counterpropagating single-mode laser beams in a thermionic diode. They measured circular polarization correlations, i.e. the dependence of the two-photon transition rate on the relative helicities of the two circularly polarized beams. The results depend strongly on the intensity of the laser driving the 7S to 15P transition and are in good agreement with theoretical predictions from a rate equation treatment taking collisional population redistributions among the 15p32/ states into account. The implications of the results for a field-free parity violation experiment are discussed.
We report here the first observation and measurement of the transition magnetic moment for a strongly forbidden S-S transition of an alkali atom. By using single-photon excitation of the 6S1/2-7S1/2 caesium transition in a quasi-static electric field, we have detected an electronic polarization of the excited state, specific to an interference effect occurring in mixed electric magnetic dipole transitions. Our measurements, independent of the vapour density, indicate that the magnetic dipole amplitude M 1 has the same size as the electric dipole amplitude E1 , induced by an electric field, parallel to the light wave polarization, and equal to 2.62 ± 0.21 V/cm. We also obtain the relative sign of M 1 and E1. Using a theoretical value of E 1 and a well-defined phase convention, we deduce for the magnetic moment of the transition < 7S, 1/ 2 | μ z | 6S, 1/ 2 > = - (4.24 ± 0.34) 10-5 |μB|, in good agreement with a theoretical estimate. This result can also be expressed in terms of the oscillator strength in zero electric field f6S-7S = 4.05 × 10-15, or of the single-photon M1 decay rate Γ 7S-6S = 0.93 x 10-6 s-1.
The authors present experimental results on the ionisation probabilities of highly excited Rydberg S and D states of caesium in collisions with ground-state Cs atoms. The measurements were done in a thermionic diode using two-photon excitation of Rydberg states with principal quantum numbers in the range 18 to 60. Over the investigated range (0.17 to 12 mTorr) a simple exponential dependence of the ionisation probabilities on binding energy and pressure was found. The authors also measured the intensity ratios of the fine-structure doublets in 6S 1/2 to nD two-photon transitions and find good agreement with theoretical calculations. From the results they conclude that the collisional ionisation probabilities are independent of orbital and total angular momentum.
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This work analyses the effects of polarization and pressure in caesium 6S–8S two-photon spectroscopy. The linewidth was broadened and the frequency was shifted by a change of polarization states. The frequency shift and the linewidth broadening of the caesium 6S–8S two-photon transition were measured as a function of laser power using one single-frequency Ti:sapphire ring cavity laser, two caesium cells and two quarter-wave plates to ensure polarization states of light, and we showed that the linewidth cannot be evaluated just by fitting data to a Lorentzian shape. As determined by fitting the data to a Voigt profile, the natural linewidth is independent of the polarization states of the pump beams, the laser power and the pressure. Caesium 6S–8S two-photon transitions pumped by a circularly polarized beam have narrower linewidths and smaller shifts than those pumped by a linearly polarized beam. The light shift obtained by pumping with the circularly polarized beam is −6.75(57) Hz (mW mm −2 ) −1 , and that obtained by pumping with a linearly polarized beam is −7.25(45) Hz (mW mm −2 ) −1 . These results agree closely with theoretical calculations. The pressure shift is −588(387) Hz mPa −1 . This work shows how to evaluate two-photon transitions with a Voigt profile, and then helps us to understand two-photon transitions with different polarization states, and improve the signal quality obtained when they are used as frequency markers.
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We have observed the direct single-photon electric dipole excitation of the 7 2S1/2 state of cesium, by exciting the 6 2S1/2 ground state in an external d. c. electric field of 10 to 1 000 V/cm with a single-mode, c. w., tunable dye laser. The resonance was detected by monitoring the decay fluorescence from the excited state. We verified the selection rules obeyed by the hyperfine transitions which depend on the relative orientation of the linear polarization of the beam with respect to the field. When they are orthogonal, the line pattern reflects the existence of a spin-dependent part of the polarizability induced by spin-orbit effects, the size of which was measured with respect to that of the scalar part. Results in very weak fields show that the oscillator strength of the 6S-7S transition is smaller than 2 x 10-13.