Ultimate parameters of an all-optical MX resonance in Cs in ultraweak magnetic field

We present the results of studying the parameters of the magnetic M-X resonance in an all-optical sensor built according to the two-beam Bell-Bloom scheme in nonzero ultraweak magnetic fields in which the effects of spin-exchange broadening suppression are partially manifested. We report on the features of the resonance under these conditions. We also optimize the resonance parameters to achieve maximum sensitivity in magnetoencephalographic sensors. We demonstrate an improvement in the ultimate achievable sensitivity of an all-optical M-X sensor by a factor of 4 or more, which in our experiment corresponds to a decrease from 13 to 3 fT/Hz(1/2) in a volume of 0.13 cm(3). We also report the effect of incomplete suppression of spin-exchange broadening under conditions of strong transverse modulated optical pumping, and propose a semiempirical model to describe it.