We have studied the ground-state Hanle effect (GSHE) excited by linearly polarized laser light on the D 1 line of cesium atoms. We have solved algebraically the Liouville equation using the irreducible tensor formalism, and derive an analytical expression for the resonance line shapes in a magnetic field of arbitrary direction. The model predictions are in excellent agreement with experimental observations in various field geometries. Our model is valid for arbitrary F → F transitions in the low-power limit. We discuss the relation between the GSHE and electromagnetically induced transparency or absorption. Our approach allows a full understanding of the mechanism of the GSHE and provides tools for quantifying the resonance contrast, a crucial parameter for metrological applications of level crossing resonances.

We describe our approach to atomic magnetometry based on the push-pull optical pumping technique. Cesium vapor is pumped and probed by a resonant laser beam whose circular polarization is modulated synchronously with the spin evolution dynamics induced by a static magnetic field. The magnetometer is operated in a phase-locked loop, and it has an intrinsic sensitivity below 20fT/ √ Hz using a room temperature paraffin-coated cell. We use the magnetometer to monitor magnetic field fluctuations with a sensitivity of 300fT/ √ Hz.A scalar atomic magnetometer measures the modulus of a static magnetic field via the Larmor frequency at which the atomic magnetic moments precess coherently. Resonant laser light is used both to create a macroscopic magnetization by orienting the atomic spins, and to detect the effect of the precessing magnetization on the medium's optical absorption coefficient.Atomic magnetometry dates back to the 1960s [1] and in the 1990s, interest in the topic resurged due to the development of compact diode lasers and microfabrication technologies. Several recent review articles have been devoted to atomic magnetometry [2][3][4].In a traditional atomic magnetometer, polarized light resonant with an atomic absorption line produces an imbalance of magnetic sublevel populations by optical pumping, thus creating spin polarization, and an associated macroscopic magnetization. In the so-called double resonance magnetometer (which may be realized in, a weak magnetic field, referred to as radio-frequency or 'rf' field, oscillating at frequency ν rf , drives transitions between neighboring Zeeman-split sublevels, thereby destroying the polarization, an effect that is resonantly enhanced when ν rf matches the Larmor frequency, ν L . This principle finds a widespread use in commercial magnetometers.One may view the rf field in the scheme outlined above as a mechanism that synchronizes the spin precession of the polarized atoms. In an alternative approach, spin synchronization is achieved by a suitable modulation of the pumping light [5] using amplitude [6], frequency [7][8][9], or polarization [10-12] modulation. The latter approaches to magnetometry yield magnetically-silent magnetometers, in which no oscillating magnetic field is applied to the sensor proper. The sensor thus does not produce any field other than the excessively weak field of the polarized atoms themselves. This is an important aspect for avoiding sensor crosstalk in multi-sensor applications.Here we present a so-called push-pull magnetometer that is based on the modulation -at the Larmor frequency -of the light beam's polarization between leftand right-circular. The original proposal of the pushpull optical pumping technique [13] aimed at increasing the contrast of the magnetically insensitive transitions in atomic clocks by polarization modulation at the clock (i.e., hyperfine transition) frequency. The method has been demonstrated for the clock transition in rubidium [14], potassium [15], and cesium [16]. So far, it has not been explored in ...

We report on light shift and broadening in the atomic-motion-induced Ramsey narrowing of dark resonances prepared in alkali-metal vapors contained in wall-coated cells without buffer gas. The atomic-motion-induced Ramsey narrowing is due to the free motion of the polarized atomic spins in and out of the optical interaction region before spin relaxation. As a consequence of this effect, we observe a narrowing of the dark resonance linewidth as well as a reduction of the ground states' light shift when the volume of the interaction region decreases at constant optical intensity. The results can be intuitively interpreted as a dilution of the intensity effect similar to a pulsed interrogation due to the atomic motion. Finally the influence of this effect on the performance of compact atomic clocks is discussed.

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Abstract:We report on a study of polarization-modulation experiments on the 4 → 3 hyperfine component of the D 1 transition in Cs vapor contained in a paraffin-coated cell. The laser beam's polarization was switched between left-and right-circular polarization at a rate of 200 Hz. Variations of the transmitted light power were recorded while varying the amplitude of a transverse magnetic field. The power shows electromagnetically induced transparency (EIT) resonances when the atomic Larmor frequency matches a harmonic of the modulation frequency. We made a quantitative study of the resonance amplitudes with square-wave modulations of various duty cycles, and find an excellent agreement with recent algebraic model predictions. References and links1. W. Bell and A. Bloom, "Optically driven spin precession," Phys. Rev. Lett. 6, 280-281 (1961). 1Published in " " which should be cited to refer to this work.http://doc.rero.ch atomic magnetometers: from gas discharge to laser pumping," Laser Phys. 251, 244-251 (1996).