Light shift suppression in a CPT magnetometer using linear polarization and double frequency interrogation

We demonstrate a suppression of the light shift in a Coherent-Population-Trapping (CPT) atomic magnetometer by using linearly polarized light and a differential measurement between magnetic resonances. The radio frequency that creates the optical sidebands for CPT quickly switches between two magnetic sensitive transitions, and the magnetic field is extrapolated from the difference of the center frequencies of the magnetic resonances. Light shifts and common drifts like collisional shifts can be suppressed through careful choice of measured resonances, and we show the light shift reduction by more than a factor of 20 compared to excitation with circularly-polarized light. Various limitations of the method are discussed.