Synchronous achievement of laser frequency stabilization and tunability via modulation transfer spectroscopy on the rubidium D₁ line

In the Spin Exchange Relaxation Free (SERF) magnetometer, the laser frequency must be stabilized at the alkali D₁ line and tunable within a range of several gigahertz (GHz). We theoretically and experimentally analyzed the modulated sideband and resonant frequencies on the D₁ transition line of rubidium (Rb) atoms using a modulation transfer spectroscopy (MTS) frequency stabilization system. The laser's self-estimated frequency stability shows the Allan deviation of 1.5 × 10⁻¹²/τ for resonance peak stabilization and 1.4 × 10⁻¹²/τ for sideband stabilization. The spectrum of the modulated laser interacting with the rubidium D₁ line exhibits several absorption peaks and MTS signals across a 6 GHz scanning frequency range, which can be used to lock and tune the laser. This method enhances the application of distributed feedback semiconductor lasers in Rb atom-based magnetometers.