  We study the absorption of monochromatic electromagnetic plane waves
impinging upon a Kerr black hole, in the general case that the direction of
incidence is not aligned with the black hole spin axis. We present numerical
results that are in accord with low- and high-frequency approximations. We find
that circularly-polarized waves are distinguished by the black hole spin, with
counter-rotating polarizations being more absorbed than co-rotating
polarizations. At low frequencies and moderate incidence angles, there exists a
narrow parameter window in which superradiant emission in the dipole mode can
exceed absorption in the non-superradiant modes, allowing a planar
electromagnetic wave to stimulate net emission from a black hole.
