Anomalous dynamic backaction in interferometers

Abstract

We analyze the dynamic optomechanical back-action in signal-recycled Michelson and MichelsonSagnac interferometers that are operated off dark port. We show that in this case -and in contrast to the well-studied canonical form of dynamic back-action on dark port -optical damping in a Michelson-Sagnac interferometer acquires a non-zero value on cavity resonance, and additional stability/instability regions on either side of the resonance, revealing new regimes of cooling/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.

Cool and Heavy

“…Instability regions are marked as yellow areas. In the second graph optical cooling on resonance is more pronounced, again in excellent agreement with our theory (solid line) [27,37]. The third graph shows a further evolution of the cooling spectrum.…”

“…Our theory predicts a well-separated cooling region at positive detunings, which, however, could not be explored in the present experiment [39]. The observed behavior of the Q factor is due to a complex structure of the radiation pressure noise spectral density: in the case of generalized optomechanical coupling this spectral density is a mixture of a Lorentz profile and a Fano profile corresponding to the dispersive and dissipative contributions, respectively [17,25,27,37]. Figure 5 shows optical cooling on resonance (measured at membrane position 3) versus input power.…”

“…Dissipative coupling can give rise to a stable optical spring (that is a positive shift of the mechanical frequency and damping) [27], as proposed in Ref. [28] for the improvement of GW [27,37]. Here, the membrane was at position 3, as described in Fig.…”

“…This adds an optically induced damping, which changes the Q factor, which is modeled in Ref. [27] and summarized in the Supplemental Material [37].…”

“…In contrast to our previous realizations of the Michelson-Sagnac topology, the present work uses an unbalanced beam splitter with a reflectivity of r 2 BS ¼ 0.53. According to theory, the unbalanced splitting is expected to increase the influence of the dissipative optomechanical coupling [27], which facilitates reaching the regime of generalized optomechanics. The movable mirror is a SiN membrane, which has a power reflectivity of r 2 m ¼ 0.17 at normal incidence at the laser wavelength of λ 0 ¼ 1064 nm.…”