Anomalous dynamic backaction in interferometers

We analyze the dynamic optomechanical backaction in signal-recycled Michelson and Michelson-Sagnac interferometers that are operated off the dark port. We show that in this case---and in contrast to the well-studied canonical form of dynamic backaction on the dark port---optical damping in a Michelson-Sagnac interferometer acquires a nonzero value on cavity resonance, and additional stability and instability regions on either side of the resonance, revealing additional regimes of cooling and heating of micromechanical oscillators. In a free-mass Michelson interferometer for a certain region of parameters we predict a stable single-carrier optical spring (positive spring and positive damping), which can be utilized for the reduction of quantum noise in future-generation gravitational-wave detectors.