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Abstract

We analyze dynamic optomechanical back-action effects in signal-recycled Michelson and Michelson-Sagnac interferometers that are operated off dark port. Up to now, their optomechanics has been studied under dark port condition only. For the dark port case and in the context of gravitational wave detectors, the `scaling law' assured that all back-action effects can be understood on the basis of the much simpler topology of a Fabry-Perot interferometer. Off dark port, our theoretical and experimental analysis reveals certain `anomalous' features as compared to the ones of `canonical' back-action, obtained within the scope of scaling law. In particular, optical damping as a function of detuning acquires a non-zero value on cavity resonance, and several stability/instability regions on either side of the cavity resonance appear. We report on the experimental observation of these instabilities on both sides of the cavity resonance in a Michelson-Sagnac interferometer with a micromechanical membrane. For a certain region of parameters, a stable optical spring (that is positive shifts of frequency and damping) in a free-mass interferometer with a single laser drive are possible. Our results can find implementations in both cavity optomechanics, revealing new regimes of cooling of micromechanical oscillators, and in gravitational-wave detectors, revealing the possibility of stable single-carrier optical spring which can be utilized for the reduction of quantum noise in future-generation detectors.