9,745 research outputs found
Parametric Instability in Long Optical Cavities and Suppression by Dynamic Transverse Mode Frequency Modulation
Three mode parametric instability has been predicted in Advanced
gravitational wave detectors. Here we present the first observation of this
phenomenon in a large scale suspended optical cavity designed to be comparable
to those of advanced gravitational wave detectors. Our results show that
previous modelling assumptions that transverse optical modes are stable in
frequency except for frequency drifts on a thermal deformation time scale is
unlikely to be valid for suspended mass optical cavities. We demonstrate that
mirror figure errors cause a dependence of transverse mode offset frequency on
spot position. Combined with low frequency residual motion of suspended
mirrors, this leads to transverse mode frequency modulation which suppresses
the effective parametric gain. We show that this gain suppression mechanism can
be enhanced by laser spot dithering or fast thermal modulation. Using Advanced
LIGO test mass data and thermal modelling we show that gain suppression factors
of 10-20 could be achieved for individual modes, sufficient to greatly
ameliorate the parametric instability problem
Numerical calculations of diffraction losses in advanced interferometric gravitational wave detectors
Knowledge of the diffraction losses in higher-order modes of large optical cavities is essential for predicting three-mode parametric photon-phonon scattering, which can lead to mechanical instabilities in long-baseline gravitational wave detectors. We explore different numerical methods in order to determine the diffraction losses of the higher-order optical modes. Diffraction losses not only affect the power buildup inside the cavity but also influence the shape and frequency of the mode, which ultimately affect the parametric instability gain. Results depend on both the optical mode shape (order) and the mirror diameter. We also present a physical interpretation of these results
Quantum ground-state cooling and tripartite entanglement with three-mode optoacoustic interactions
We present a quantum analysis of three-mode optoacoustic parametric
interactions in an optical cavity, in which two orthogonal transverse
optical-cavity modes are coupled to one acoustic mode through radiation
pressure. Due to the optimal frequency matching -- the frequency separation of
two cavity modes is equal to the acoustic-mode frequency -- the carrier and
sideband fields simultaneously resonate and coherently build up. This mechanism
significantly enhances the optoacoustic couplings in the quantum regime. It
allows exploration of quantum behavior of optoacoustic interactions in
small-scale table-top experiments. We show explicitly that given an
experimentally achievable parameter, three-mode scheme can realize quantum
ground-state cooling of milligram scale mechanical oscillators and create
robust stationary tripartite optoacoustic quantum entanglements.Comment: 20 pages, 5 figure
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