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Journal de physique

Laser diode optically pumped caesium beam

Emeric de Clercq, M. de Labachellerie, G. Ávila, P. Cérez, M. Têtu

Published Jan 1, 1984• 51 citations

Abstract

This paper presents a theoretical analysis of a possible scheme to realize a strong population difference between the two ground state sub-levels F = 4, MF = 0, and F = 3, MF = 0 of caesium atom. Two laser-diode light beams, π polarized, are used to illuminate at right angle an atomic beam. The efficiency of the population difference build up is evaluated for two limiting cases according to the light spectral distribution : the monochromatic and broadband excitations. This analysis takes into account hyperfine and Zeeman structures of the energy levels. Numerical calculations show that the monochromatic excitation leads to steady state population difference close to the value obtained with a single pumping laser; however all the atoms can be brought in the upper level if the two laser lights are considered broadband and uncorrelated Guidelines are derived to obtain an efficient optically pumped caesium beam frequency standard.

DOI: 10.1051/jphys:01984004502023900

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This paper presents a theoretical analysis of a possible scheme to realize a strong population difference between the two ground state sub-levels F = 4, MF = 0, and F = 3, MF = 0 of caesium atom. Two laser-diode light beams, π polarized, are used to illuminate at right angle an atomic beam. The efficiency of the population difference build up is evaluated for two limiting cases according to the light spectral distribution : the monochromatic and broadband excitations. This analysis takes into account hyperfine and Zeeman structures of the energy levels. Numerical calculations show that the monochromatic excitation leads to steady state population difference close to the value obtained with a single pumping laser; however all the atoms can be brought in the upper level if the two laser lights are considered broadband and uncorrelated Guidelines are derived to obtain an efficient optically pumped caesium beam frequency standard.

Two-laser optical pumping schemes show great promise for atom preparation since they can act as a nearly perfect state selector. This paper presents a new theoretical model to evaluate the pumping efficiency of two-laser pumping schemes, taking into account optical, ground and excited states hyperfine and Zeeman coherences, neighboring transitions, and fluctuating laser fields. The model is used to predict the optical pumping efficiency of two lasers with Lorentzian spectral profiles on a beam of cesium atoms. The particular laser intensities and linewidths that optimize the optical pumping efficiency and rate are calculated.

In this paper the optical pumping of a cesium beam is investigated. The rate equation model is used to calculate the population difference created by laser diode(s) illuminating the beam. The finite laser and atomic linewidths are taken into account in order to analyze leakage effects on neighboring transitions. One-laser and two-laser pumping is considered and the best-suited two-laser configurations for preparing the cesium atoms in a single

{m}_{F}

=0 sublevel are specified. Experimental results on both the leakage effect and the population difference achieved agree with theoretical predictions.

It is experimentally demonstrated that, using diode lasers for optical pumping and RF /spl pi/-pulses for population transfer, nearly all of the ground state Rb atoms in a vapor cell can be concentrated into one of the two M/sub F/ = 0 sublevels. The fractional population difference /spl Delta/ between the two M/sub F/ = 0 levels can be made as high as 1. This should result in a very significant improvement (about a factor of 100) in the S/N over the conventional discharge-lamp-pumped rubidium frequency standards (RFSs). This would lead to a substantial improvement in the short-term stability of the RFS. This is a pulsed population transfer scheme. The microwave interrogation takes place in the absence of strong pumping light. This has the potential for eliminating the light shift and thereby improving the long-term frequency stability of a an RFS.>

We investigate the population differences between ground-state hyperfine levels (

{5S}_{1/2},F=2

and

{5S}_{1/2},

F=1

) of an optically pumped

{5S}_{1/2},F=2

beam in a static magnetic field, taking into account the various kinds of atomic coherence (Zeeman, hyperfine, and optical). The pumping lasers are monochromatic and in resonance with the ${(5S}_{1/2},F=1\ensuremath{\leftrightarrow}{5P}_{1/2}{,F}^{\ensuremath{'}}=1)$ transition. By varying the polarization configuration of the pumping lasers, we find that the pumping efficiency is substantially enhanced when a $\ensuremath{\sigma}$-polarized laser and a $\ensuremath{\pi}$-polarized laser are counterpropagating. In this case, the pumping efficiency remains high even in a weak magnetic field, which explains qualitatively experimental data reported previously from a cesium beam experiment.

This paper reports an analytical calculation of the populations of the Zeeman sublevels of the cesium atom. We use a circularly polarized laser beam to pump the Cs-cell in the geomagnetic field. Using the approximate form of the optical Bloch equations, we obtain the time evolution functions of the populations of the Zeeman sublevels S1/2(F=4, mF=-4) and P1/2(F=4, mF=-3). The case of the laser detuning of δ=0, by increasing the pumping light intensity, we could enhance populations non-uniform distribution degree of the ground states and improve the pumping efficiency of the cesium atom. It is significant to enhance sensitivity and accuracy of the optically pumped magnetometer.