  Parametric Instability (PI) is a phenomenon that results from resonant
interactions between optical and acoustic modes of a laser cavity. This is
problematic in gravitational wave interferometers where the high intra-cavity
power and low mechanical loss mirror suspension systems create an environment
where three mode PI will occur without intervention. We demonstrate a technique
for real time imaging of the amplitude and phase of the optical modes of PI
yielding the first ever images of this phenomenon which could form part of
active control strategies for future detectors.
