We experimentally demonstrate that the sensitivity of all-optical Faraday-rotation magnetometer can be improved by tuning probe light frequency to the edge of wings of Doppler profile with cesium atoms, which coincides with the theoretical analysis.
An all-optical cesium magnetometer with high sensitivity based on absorptive detection is reported. The experiment achieves a polarized rotational spectrum of the probe light which is induced by circular dichroism and a quarter wave plate together. The frequency response of the rotational spectrum is 1.8 mrad/Hz at Larmor precession resonance. Analyzing the signal-to-noise ratio from the experimentally observed spectrum, we predict that the magnetic measurement sensitivity of 0.3 pT/Hz 1/2 would be obtained in the responsive range from 20 nT to 2000 nT.
We propose a far off-resonance laser frequency stabilization method that can accurately adjust the frequency lock points based on the Faraday rotation spectroscopy. The atomic magnetometer based on the spin-exchange relaxation-free (SERF) theory needs to stabilize the frequency of the probe laser on the detuning of several gigahertz (GHz) away from the resonance of the alkali metal atom, to reduce the absorption of the probe light by the alkali metal vapor cell. We propose a laser frequency stabilization method that can accurately adjust the frequency lock points using an acousto-optic modulator based on Faraday rotation spectroscopy. We reveal the principles of the method and simulate the new Faraday rotation spectra. Besides, we study the effect of the amount of frequency shift of the acousto - optic modulator and the temperature of the alkali metal vapor cell on the frequency lock points of the spectra, and give the formula for calculating the frequency point. Our proposed laser frequency stabilization method can stabilize the laser frequency on the detuning of several gigahertz (GHz) away from the resonance of the alkali metal atom and can adjust the frequency lock points quickly and accurately. This method can be used in atomic magnetometer, degenerate Raman sideband cooling (DRSC) and two photon excitation of Rydberg states.
Polarization rotation of weak probe light induced by circularly polarized strong coupling light in a $\ensuremath{\Lambda}$ configuration is studied. We use spin-polarized cold cesium atoms trapped in a magneto-optical trap to remove complications from Zeeman distribution, Doppler broadening, and collisional decoherence. By using a very low probe intensity and short illumination period we work in a strictly linear regime. The probe and the coupling fields are optically phase locked to eliminate phase fluctuation and consequent atomic decoherence. Using this idealized situation we clarify the roles of optically induced Faraday rotation, circular dichroism, and electromagnetically induced transparency (EIT) in determining the final state of the probe light. In particular, we identify an experimental situation where the roles of atomic coherence and EIT are important.
Recently, atomic magnetometers have been reported as the most sensitive magnetometers by completely eliminating the spin exchange relaxation. In this paper, we described a design of highly sensitive cesium atomic magnetometer based on circular dichroism, which had the advantage of easily locking the probing laser to the necessary frequency compared with those based on circular birefringence. In order to polarize the cesium atoms uniformly, the pumping laser light was separated into two counter-propagating and counter-circular polarization beams through the atomic vapor cell. We employed a circular analyzer optical configuration to measure the ellipticity of the probing light, which indicated the amplitude of the magnetic field. The external magnetic field was tracked by a digital auto frequency tracking system.
Recently, atomic magnetometers have been researched widely for its ultra high sensitivity. But the influence of pump light’s duty cycle on atomic magnetometers has been concerned little. In this paper, we described a sensitive cesium atomic magnetometer based on circular dichroism, which had the advantage of easily locking the probing laser to the necessary frequency. We experimentally investigated the amplitudes and linewidths of magnetic resonance signals at different modulated duty cycle of the pump light. The result indicated that our magnetometer achieved the highest sensitivity at the duty cycle of 30%. It’s valuable for optimizing the sensitivity of most atomic magnetometers.