FID Magnetometer Based on Paraffin-Coated Planar Reflective Multipass Cells

TL;DR

This paper introduces a compact, paraffin-coated planar multipass vapor cell for optical atomic magnetometry, achieving high sensitivity and long coherence times suitable for integrated magnetometers.

Contribution

The work demonstrates a novel planar geometry multipass cell with high optical depth and long spin relaxation times, enabling ultrasensitive, compact atomic magnetometers.

Findings

Achieved 10 pT/√Hz sensitivity in geomagnetic fields.

Two-cell differential setup reached 28 fT/√Hz sensitivity in 1-15 Hz band.

Maintained spin-relaxation time longer than 1 second.

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.