  As scanning tunneling microscopy is pushed towards fast local dynamics, a
quantitative understanding of tunnel junctions under the influence of a fast AC
driving signal is required, especially at the ultra-low temperatures relevant
to spin dynamics and correlated electron states. We subject a
superconductor-insulator-superconductor junction to a microwave signal from an
antenna mounted \textit{in situ} and examine the DC response of the contact to
this driving signal. Quasi-particle tunneling and the Josephson effect can be
interpreted in the framework of Tien-Gordon theory. The situation is more
complex when it comes to higher order effects such as multiple Andreev
reflections. Microwave assisted tunneling unravel these complex processes,
providing deeper insights into tunneling than are available in a pure DC
measurement.
