Precursors of parametric oscillatory instability in LIGO interferometer

The basis of undesirable effect of parametric oscillatory instability in optical interferometer is provided by excitation of the additional (Stokes) optical mode having frequency ω1ω1, and the mirror elastic mode, having frequency ωmωm. It appears when optical energy stored in the main mode, with frequency ω0ω0, exceeds a certain threshold and the frequencies are related as ω0≃ω1+ωmω0≃ω1+ωm. We analyze the time evolution of parametric instability which allows predicting the characteristics of precursors of parametric instability. Observation of such precursors may help avoid parametric instability.