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Absolute frequency of cesium 6S-8S hyperfine transition by two-photon interfered spectrum

Chien-Ming Wu, Tze-Wei Liu, Ray‐Kuang Lee, Wang-Yau Cheng

Published Jan 1, 2013• 0 citations
Publisher

Abstract

We present a novel two-photon spectrum in which the transition amplitude was interfered with phase-modulated radiation. We demonstrate the application of our resolved spectrum by determining the absolute frequency of cesium 6S-8S hyperfine transitions.
DOI
10.1364/cleo_qels.2013.qth4c.2

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An alternate method of two-photon spectroscopy is presented where cesium atoms interact with a phase-modulated laser beam. Doppler-free two-photon spectroscopy of the cesium atom $6S\ensuremath{\rightarrow}8S$ hyperfine transition was used to experimentally demonstrate quantum interfered two-photon spectra. We calculated the photon-atom interaction by second-order perturbation theory and assumed that the one-photon frequency is detuned far from any intermediate state. Then we calculated the relative transition rates of all spectral lines resolved by the laser carrier and sidebands. A physical picture of multipathway quantum interference in the frequency domain is given that explains the unusual line strength, based on the trick that a phase-modulated laser beam can be decomposed into a series of coherent and collinear laser modes (carrier and sidebands). For all pairs of modes in which the sum frequency of each pair was on resonance with the cesium atom $6S\ensuremath{\rightarrow}8S$ transition, the superposition of all pathways induced by the different mode pairs resulted in a destructive interference, which then leads to a lack of absorption. We have shown in this paper that our calculation agrees very well with our experimental results in terms of the relative interfered line strengths, which were functions of modulation depth. We further discuss some related issues concerning laser stabilization and we demonstrate an approach for simultaneously comparing two cesium cells.
The probability of a two-photon absorption (TPA) process is quantified by means of the TPA cross-section. In this work the TPA cross-section for the 6 S 1/2 → 8 S 1/2 transition in cesium (Cs) atoms is obtained from a theoretical and experimental approach. It is calculated using second order perturbation theory including hyperfine structure and Doppler broadening for a thermal atomic vapor. The theoretical values for the TPA cross-sections of the two allowed hyperfine transitions are σ ~ 3,3 =3.10×10 −24 cm 4 /W and σ ~ 4,4 =3.65×10 −24 cm 4 /W. An experiment is set up to measure these cross-sections based on the quadratic dependence between the TPA transition rate and the intensity of the laser light. Values of σ ~ 3,3 =(3.6±1.1)×10 −24 cm 4 /W and σ ~ 4,4 =(4.6±1.1)×10 −24 cm 4 /W are obtained from the measurements. The results show an agreement between theory and experiment. To the best of our knowledge, this is the first time that these cross-sections are reported.
Abstract Using a Rb cell and a wavemeter, with a Doppler-free two-photon transition near 993 nm, we have measured the four hyperfine components (two isotopes, Δ F = 0) of the 5S–6S transition, finding the absolute energies of those transitions to a spectral resolution of 0.002 cm −1 = 60 MHz. We find the (87 minus 85) isotope shift of the 5S–6S transition to be +94(12) MHz. Using our single frequency cw laser with focused intensity up to 10 4 W cm −2 at the cell, we find no AC Stark or light shift of the lines at 6 MHz spectral resolution. We find no density shift of the lines at 6 MHz spectral resolution, for a range of Rb atom densities from 3 × 10 11 to 5 × 10 13 atoms/cm 3 .