Parametric oscillatory instability in a signal-recycled LIGO interferometer

The undesirable effect of parametric oscillatory instability in a LIGO (Laser Interferometer Gravitational-Wave Observatory) laser gravitational-wave antenna with a signal-recirculation mirror is analysed in detail. The instability is manifested in excitation of the Stokes optical mode and elastic mechanical mode of the mirror. It is shown that, if the eigenfrequencies of Fabry–Perot resonators in the interferometer arms are different, the parametric instability is quite small due to a small passband band width.