We demonstrate a new mechanism, suitable for performing remote earth field measurement using synchronous modulation of two laser fields, which are two-photon resonant with the sodium atom’s hyperfine ground states. This mechanism relies on coherent population trapping (CPT), and thus, called the synchronous CPT scheme. We have measured the magnetic resonances in fluorescence from a sodium cell to demonstrate suitability of this scheme for remote magnetometry. A strong magnetic resonance with its dip corresponding to the Larmor frequency is produced in the presence of a transverse magnetic field. To estimate the optimal duty cycle of light modulation for attaining high performance, we measured the amplitudes and linewidths of the magnetic resonance as a function of the duty cycle, by keeping the peak intensity in CPT fields constant.
We report our investigations on the dependence of magnetic resonance spectrum on the light ellipticity and the polarization angle. A rubidium vapor cell with octade-cyltrichlorosilane (OTS) antirelaxation coating has been used in our experiment to produce narrow linewidth magnetic resonances. We show that excitation using elliptically polarized light can simultaneously produce the alignment and orientation resonances in a Bell-Bloom interaction geometry. We have developed a theoretical model to calculate the resonance spectrum using light with a varying degree of ellipticity. Amplitudes of the alignment and orientation resonances show a strong dependence on the light ellipticity. Our study shows that the duty cycle of light modulation can effectively control the amplitude variations of the alignment and orientation resonances with light ellipticity. We propose that the difference between the alignment and orientation resonance amplitudes can be used for in situ measurement of the light
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