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arXiv:2405.10715 · Physical Review Applied

Functionalized millimeter-scale vapor cells for alkali-metal spectroscopy and magnetometry

Harini Raghavan, Michael C. D. Tayler, K. Mouloudakis, Rachel Rae, Sami Lähteenmäki, Rasmus Zetter, Petteri Laine, Jacques Haesler, Laurent P. Balet, Thomas Overstolz, Sylvain Karlen, Morgan W. Mitchell

Published Oct 4, 2024• 21 citations
arXivHTMLPDF

Abstract

We describe microfabricated rubidium vapor cells with integrated temperature-control functionality and demonstrate their suitability for use in miniaturized ultrasensitive magnetometers. These functionalized vapor cells (FVCs) embody a dual-chamber design in low-conductivity silicon with antipermeation coatings and microstructured thin-film platinum surface traces as resistive heaters and temperature sensors. Thermal tests show our ability to control alkali-metal distribution within the FVCs, ensuring a clean sensing chamber for optical measurements. Optical-absorption spectroscopy is used to correlate the temperature readings with vapor density and to measure buffer-gas pressure, of interest for optimizing sensitivity. Finally, we demonstrate zero-field resonance magnetometry with $18\phantom{\rule{0.1em}{0ex}}\mathrm{fT}/\sqrt{\mathrm{H}}\mathrm{z}$ sensitivity in the 10- to 100-Hz band, limited by laser noise and magnetic shield noise, which indicates that the functionalization does not introduce significant magnetic noise.

DOI
10.1103/physrevapplied.22.044011

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Abstract Microfabricated alkali vapor cells enable the miniaturization of atomic sensors, but require collective wafer-level integration of complex features. In many applications-including magnetometers, gyroscopes, magneto-optical traps, and fluorescence imaging-multiple optical accesses are needed to enhance performance. Yet, achieving this without compromising manufacturability remains challenging. In this work, we present a wafer-level fabrication approach that enables three orthogonal optical pathways in microfabricated alkali vapor cells, using fully scalable and collective processes. Our method relies on the thermal reflow of glass preforms, shaped by laser-assisted etching (LAE) and bonded between silicon frames. The relatively low surface roughness produced by LAE allows for effective reflow, which further smooths the surfaces without significantly compromising the optical planarity of the windows. This process results in multi-axis vapor cells featuring embedded, optics-grade lateral windows. We evaluate the device performance through both single-beam and dual-beam atomic magnetometry measurements. Magnetic sensitivities better than 200 fT Hz − 1 are demonstrated along each of the three orthogonal axes, confirming the potential of the approach for tri-axis magnetic field sensing at sub-picotesla resolution. This fabrication strategy opens new perspectives for versatile, high-performance atomic sensors, fully compatible with wafer-level integration and mass production.
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