FID Magnetometer Based on Paraffin-Coated Planar Reflective Multipass Cells

Abstract

We demonstrate a paraffin-coated planar reflective multipass vapor cell for compact optical atomic magnetometry. The cell has an internal volume of $12\times 12\times 8{\mathrm{mm}}^3$ and supports 20 optical passes with a total transmittance exceeding $65\%$, while maintaining a longitudinal spin-relaxation time of ${}^{87}\mathrm{Rb}$ longer than $1\mathrm{s}$. The planar geometry provides spatially separated input and output beams, enabling compact optical integration. A single-cell free-induction-decay (FID) magnetometer reaches $10\mathrm{pT}/\sqrt{\mathrm{Hz}}$ in the geomagnetic-field range, presently limited by current-source noise in the field coils. A two-cell differential configuration achieves a sensitivity of $\sim 28\mathrm{fT}/\sqrt{\mathrm{Hz}}$ over the $1$--$15\mathrm{Hz}$ band for bias fields of $0.3$--$0.7\mathrm{G}$. These results establish that paraffin-coated planar multipass cells offer high optical depth, long coherence times, and an integration-friendly platform for ultrasensitive magnetometry.

8 pages, 7 figures