Imaging Microwave and DC Magnetic Fields in a Vapor-Cell Rb Atomic Clock

TL;DR

This paper demonstrates a method to image and analyze the spatial distribution of microwave and DC magnetic fields inside a vapor-cell Rb atomic clock using optical-microwave Rabi and Ramsey measurements, achieving high spatial resolution.

Contribution

It introduces a novel in-situ imaging technique for magnetic fields within atomic clock components, enabling detailed characterization of field distributions and relaxation times.

Findings

Microwave field images with sub-100 μm resolution were obtained.

DC magnetic field distribution was mapped using Ramsey measurements.

The T2 relaxation time varies with position and correlates with magnetic field gradients.

Abstract

We report on the experimental measurement of the DC and microwave magnetic field distributions inside a recently-developed compact magnetron-type microwave cavity, mounted inside the physics package of a high-performance vapor-cell atomic frequency standard. Images of the microwave field distribution with sub-100 $\mu$m lateral spatial resolution are obtained by pulsed optical-microwave Rabi measurements, using the Rb atoms inside the cell as field probes and detecting with a CCD camera. Asymmetries observed in the microwave field images can be attributed to the precise practical realization of the cavity and the Rb vapor cell. Similar spatially-resolved images of the DC magnetic field distribution are obtained by Ramsey-type measurements. The T2 relaxation time in the Rb vapor cell is found to be position dependent, and correlates with the gradient of the DC magnetic field. The presented method is highly useful for experimental in-situ characterization of DC magnetic fields and resonant microwave structures, for atomic clocks or other atom-based sensors and instrumentation.