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Register a new userA novel concept for increasing the peak sensitivity of LIGO by detuning the arm cavities
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We introduce a concept that uses detuned arm cavities to increase the shot noise limited sensitivity of LIGO without increasing the light power inside the arm cavities. Numerical simulations show an increased sensitivity between 125 and 400 Hz, with a maximal improvement of about 80% around 225 Hz, while the sensitivity above 400Hz is decreased. Furthermore our concept is found to give a sensitivity similar to that of a conventional RSE configuration with a Signal-Recycling mirror of moderate reflectivity. In the near future detuned arm cavities might be a beneficial alternative to RSE, due the potentially less hardware intensive implementation of the proposed concept.
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Several large-scale interferometric gravitational-wave detectors use resonant arm cavities to enhance the light power in the interferometer arms. These cavities are based on different optical designs: One design uses wedged input mirrors to create additional optical pick-off ports for deriving control signals. The second design employs input mirrors without wedge and thus offers the possibility to use the etalon effect inside the input mirrors for tuning the finesse of the arm cavities. In this article we introduce a concept of maximized flexibility that combines both of these options, by featuring wedges at the input mirrors and using the etalon effect instead in the end mirrors. We present a design for the arm cavities of Advanced Virgo. We have used numerical simulations to derive requirements for the manufacturing accuracy of an end mirror etalon for Advanced Virgo. Furthermore, we give analytical approximations for the achievable tuning range of the etalon in dependence on the reflectance, the curvature and the orientation of the etalon back surface.
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Vacuum quantum fluctuations impose a fundamental limit on the sensitivity of gravitational-wave interferometers, which rank among the most sensitive precision measurement devices ever built. The injection of conventional squeezed vacuum reduces quantum noise in one quadrature at the expense of increasing noise in the other. While this approach improved the sensitivity of the Advanced LIGO and Advanced Virgo interferometers during their third observing run (O3), future improvements in arm power and squeezing levels will bring radiation pressure noise to the forefront. Installation of a filter cavity for frequency-dependent squeezing provides broadband reduction of quantum noise through the mitigation of this radiation pressure noise, and it is the baseline approach planned for all of the future gravitational-wave detectors currently conceived. The design and operation of a filter cavity requires careful consideration of interferometer optomechanics as well as squeezing degradation processes. In this paper, we perform an in-depth analysis to determine the optimal operating point of a filter cavity. We use our model alongside numerical tools to study the implications for filter cavities to be installed in the upcoming A+ upgrade of the Advanced LIGO detectors.
We introduce a novel test of General Relativity in the strong-field regime of a binary black hole coalescence. Combining information coming from Numerical Relativity simulations of coalescing black hole binaries with a Bayesian reconstruction of the gravitational wave signal detected in LIGO-Virgo interferometric data, allows one to test theoretical predictions for the instantaneous gravitational wave frequency measured at the peak of the gravitational wave signal amplitude. We present the construction of such a test and apply it on the first gravitational wave event detected by the LIGO and Virgo Collaborations, GW150914. The $p$-value obtained is $p=0.48$, to be contrasted with an expected value of $p=0.5$, so that no signs of violations from General Relativity were detected.
A first detection of terrestrial gravity noise in gravitational-wave detectors is a formidable challenge. With the help of environmental sensors, it can in principle be achieved before the noise becomes dominant by estimating correlations between environmental sensors and the detector. The main complication is to disentangle different coupling mechanisms between the environment and the detector. In this paper, we analyze the relations between physical couplings and correlations that involve ground motion and LIGO strain data h(t) recorded during its second science run in 2016 and 2017. We find that all noise correlated with ground motion was more than an order of magnitude lower than dominant low-frequency instrument noise, and the dominant coupling over part of the spectrum between ground and h(t) was residual coupling through the seismic-isolation system. We also present the most accurate gravitational coupling model so far based on a detailed analysis of data from a seismic array. Despite our best efforts, we were not able to unambiguously identify gravitational coupling in the data, but our improved models confirm previous predictions that gravitational coupling might already dominate linear ground-to-h(t) coupling over parts of the low-frequency, gravitational-wave observation band.
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