  We propose to use a point contact between a ferromagnetic and a normal metal
in the presence of a magnetic field for creating a large inverted
spin-population of hot electrons in the contact core. The key point of the
proposal is that when these hot electrons relax by flipping their spin,
microwave photons are emitted, with a frequency tunable by the applied magnetic
field. While point contacts is an established technology their use as a photon
source is a new and potentially very useful application. We show that this
photon emission process can be detected by means of transport spectroscopy and
demonstrate stimulated emission of radiation in the 10-100 GHz range for a
model point contact system using a minority-spin ferromagnetic injector. These
results can potentially lead to new types of lasers based on spin injection in
metals.
