Imaging microwave and DC magnetic fields in a vapor-cell Rb atomic clock

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-μm 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.