  Here we report on measurements of the absolute absorption and dispersion
properties of an isotopically pure 87Rb vapour for magnetic fields up to and
including 0.6 T. We discuss the various regimes that arise when the hyperfine
and Zeeman interactions have different magnitudes, and show that we enter the
hyperfine Paschen- Back regime for fields greater than 0.33 T on the Rb D2
line. The experiment uses a compact 1 mm3 microfabricated vapour cell that
makes it easy to maintain a uniform and large magnetic field with a small and
inexpensive magnet. We find excellent agreement between the experimental
results and numerical calculations of the weak probe susceptibility where the
line positions and strengths are calculated by matrix diagonalization.
