  Axions and axion-like particles generically couple to QED via the
axion-photon-photon interaction. This leads to a modification of Maxwell's
equations known in the literature as axion-electrodynamics. The new form of
Maxwell's equations gives rise to a new parametric instability in which a
strong pump decays into a scattered light wave and an axion. This axion mode
grows exponentially in time and leads to a change in the polarisation of the
initial laser beam, therefore providing a signal for detection. Currently
operating laser systems can put bounds on the axion parameter space, however
longer pulselengths are necessary to reach the current best laboratory bounds
of light-shining through wall experiments.
