  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.
