We describe an optically pumped Cs magnetometer containing a $1.5\text{−}\mathrm{mm}$-thick microfabricated vapor cell with nitrogen buffer gas operating in a free-induction-decay configuration. This allows us to monitor the free Larmor precession of the spin-coherent Cs atoms by separating the pump and probe phases in the time domain. A single light pulse can sufficiently polarize the atomic sample; however, synchronous modulation of the light field actively drives the precession and maximizes the induced spin coherence. Both amplitude and frequency modulation have been implemented with noise floors of 3 and $16\mathrm{pT}/\sqrt{\mathrm{Hz}}$, respectively, within the Nyquist-limited bandwidth of $500\mathrm{Hz}$.

• Received 25 September 2017
• Revised 21 December 2017
• Corrected 6 July 2018

DOI:https://doi.org/10.1103/PhysRevApplied.10.014002