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Gravitational waves from the neutron star coalescence GW170817 were observed from the inspiral, but not the high frequency postmerger nuclear matter motion. Optomechanical white light signal recycling has been proposed for achieving broadband sensitivity in gravitational wave detectors, but has been reliant on development of suitable ultra-low loss mechanical components. Here we show demonstrated optomechanical resonators that meet loss requirements for a white light signal recycling interferometer with strain sensitivity below 10−24 Hz−1/2 at a few kHz. Experimental data for two resonators are combined with analytic models of interferometers similar to LIGO to demonstrate enhancement across a broader band of frequencies versus dual-recycled Fabry-Perot Michelson detectors. Candidate resonators are a silicon nitride membrane acoustically isolated by a phononic crystal, and a single-crystal quartz acoustic cavity. Optical power requirements favour the membrane resonator, while thermal noise performance favours the quartz resonator. Both could be implemented as add-on components to existing detectors. Gravitational wave astronomy is on a path to increase the sensitivity and bandwidth of their detectors to afford the possibility to study a larger variety of sources and physical processes. The authors present solutions to enhance the sensitivity of a laser interferometric gravitational wave detector in the frequency band of 1-5 kHz using optomechanics-based white light signal recycling technologies, overcoming previous limitations of signal recycling. [ABSTRACT FROM AUTHOR]

In many sensitive measurement systems such as gravitational wave detectors, multistage low-loss vacuum-compatible suspension chains are required to effectively isolate the test mass from seismic disturbances. These chains usually have high quality factor normal modes which require damping. A technique termed "self-damping" in which the motion of orthogonal modes of the same stage mass is deliberately viscously cross-coupled to each other—thereby damping both modes—was engineered into the suspension chains used in an 80 m suspended high-power optical cavity. In this report, we investigate in detail the performance of a single stage of these chains. We model the system using numerical simulation and compare this with experimental measurements with different damping parameters in order to optimize the self-damping obtained using this technique. [ABSTRACT FROM AUTHOR]

Low acoustic loss suspension systems are essential components in low thermal noise instruments including gravitational wave detectors. Monolithic fused silica suspensions have been used successfully with fused silica test masses but may not be suitable in next generation detectors that may use sapphire or silicon test masses. Here we report a study of a modular suspension system with high replaceability. The system is based on high pressure gravitationally attached mechanical contacts which have been previously shown to contribute low acoustic losses to sapphire resonators. Here we combine high pressure contacts with cantilevers and fibres to create sets of four suspension modules which are shown to have low loss contributions to fused silica test masses in a 74-m high-finesse optical cavity. Results are combined with finite element simulations to estimate the strain energy distributions of the eigenmodes. By combining the simulations and measurement results, the test mass loss angle due to the coupling to the suspension system was estimated. The modular suspension system is shown to contribute <10% to the total test mass acoustic loss. Such suspension systems could have applications for test masses or subsystems in next generation gravitational wave detectors. [ABSTRACT FROM AUTHOR]

We present a new rotational vibration isolator with an extremely low resonant frequency of 0.055 ± 0.002 Hz. The isolator consists of two concentric spheres separated by a layer of water and joined by very soft silicone springs. The isolator reduces rotation noise at all frequencies above its resonance which is very important for airborne mineral detection. We show that more than 40 dB of isolation is achieved in a helicopter survey for rotations at frequencies between 2 Hz and 20 Hz. Issues affecting performance such as translation to rotation coupling and temperature are discussed. The isolator contains almost no metal, making it particularly suitable for electromagnetic sensors. [ABSTRACT FROM AUTHOR]

This paper reports a comprehensive study on the gravitational wave (GW) background from compact binary coalescences. We consider in our calculations newly available observation-based neutron star and black hole mass distributions and complete analytical waveforms that include post-Newtonian amplitude corrections. Our results show that: (i) post-Newtonian effects cause a small reduction in the GW background signal; (ii) below 100 Hz the background depends primarily on the local coalescence rate r0 and the average chirp mass and is independent of the chirp mass distribution; (iii) the effects of cosmic star formation rates and delay times between the formation and merger of binaries are linear below 100 Hz and can be represented by a single parameter within a factor of ∼2; (iv) a simple power-law model of the energy density parameter ΩGW(f ) ∼ f 2/3 up to 50–100 Hz is sufficient to be used as a search template for ground-based interferometers. In terms of detection prospects of this background signal, we show that: (i) detection (a signal-to-noise ratio of 3) within one year of observation by the Advanced Laser Interferometer Gravitational-wave Observatory (LIGO) detectors (H1-L1) requires a coalescence rate of r0 = 3 (0.2) Mpc−3 Myr−1 for binary neutron stars (binary black holes); (ii) this limit on r0 could be reduced threefold for two co-located and co-aligned detectors, whereas the currently proposed worldwide network of advanced instruments gives only ∼30 per cent improvement in detectability; (iii) the improved sensitivity of the planned Einstein Telescope allows not only confident detection of the background but also the high-frequency components of the spectrum to be measured, possibly enabling rate evolutionary histories and mass distributions to be probed. Finally, we show that sub-threshold binary neutron star merger events produce a strong foreground, which could be an issue for future terrestrial stochastic searches of primordial GWs. [ABSTRACT FROM AUTHOR]

High optical power is necessary to increase the sensitivity of advanced gravitational wave detectors. However, it will also induce instabilities. In this paper we review the effects caused by high optical power and potential methods to control those instabilities. Some recent experimental results are presented. [ABSTRACT FROM AUTHOR]

We report on a seismic isolator with a relatively compact 3 m stack, combining new passive isolation techniques. It consists of three cascaded passive 3D isolator stages suspended from an Ultra Low Frequency (ULF) horizontal Robert linkage stage which itself is suspended from a ULF 3D pre-isolator. The 3D isolators use self-damping pendulums and Euler springs for the horizontal and vertical stages respectively, while the 3D pre-isolator is the combination of an inverse pendulum which provides low frequency horizontal pre-isolation, and a LaCoste linkage for low frequency vertical pre-isolation. Two isolators suspending mirror test masses have been built to form a 72 m optical cavity in order to test their performance. We report results which demonstrate residual motion at nanometer level at frequencies above 1 Hz. [ABSTRACT FROM AUTHOR]

High performance vibration isolators are required for ground based gravitational wave detectors. To attain very high performance at low frequencies we have developed multistage isolators for the proposed Australian International Gravitational Observatory detector in Australia. New concepts in vibration isolation including self-damping, Euler springs, LaCoste springs, Roberts linkages, and double preisolation require novel sensors and actuators. Double preisolation enables internal feedback to be used to suppress low frequency seismic noise. Multidegree of freedom control systems are required to attain high performance. Here we describe the control components and control systems used to control all degrees of freedom. Feedback forces are injected at the preisolation stages and at the penultimate suspension stage. There is no direct actuation on test masses. A digital local control system hosted on a digital signal processor maintains alignment and position, corrects drifts, and damps the low frequency linear and torsional modes without exciting the very high Q-factor test mass suspension. The control system maintains an optical cavity locked to a laser with a high duty cycle even in the absence of an autoalignment system. An accompanying paper presents the mechanics of the system, and the optical cavity used to determine isolation performance. A feedback method is presented, which is expected to improve the residual motion at 1 Hz by more than one order of magnitude. [ABSTRACT FROM AUTHOR]

Magnetic gradiometers are tools for geophysical exploration. The magnetic gradient is normally calculated by subtracting the outputs of two total field magnetometers which are separated by a baseline. Here we present a unique device that directly measures magnetic gradients using only a single string as its sensing element. The main advantage of a direct string magnetic gradiometer is that only gradients can induce second harmonic string vibrations. A high common mode rejection ratio is thus naturally achieved without any balancing technique. Performance depends on the ability to dissipate heat while minimizing air damping. By combining high current, an elevated temperature and low pressure, we can easily achieve sensitivity of [formula]. Further increases in sensitivity can be attained by optimizing the sensing element. In this paper we present an in-depth study of the most critical parameters of the magnetic gradiometer. We describe the design for the next generation of sensor, which will reach the required sensitivity of [formula] using only 1 W of power. By combining a few single-axis magnetic gradiometer modules, it will be possible to deploy a full tensor magnetic gradiometer with more than sufficient sensitivity for airborne geophysical applications. [ABSTRACT FROM AUTHOR]

To prevent electrical wiring from mechanically short circuiting in the high performance vibration isolators for gravitational wave detection, we designed a telemetry system. The system provides wireless signal transmission and radiation power supplies. A consideration of heat dissipation of in-vacuum electronic components is presented. The preliminary experiments demonstrated that the telemetry system is feasible. [ABSTRACT FROM AUTHOR]

This article describes an automatic Rayleigh scattering mapping system (ARSMS), which enables quantitative high-resolution three-dimensional mapping of inhomogeneities in optical materials. The ARSMS allows large high-grade test mass samples for gravitational wave detectors to be evaluated to ensure that an adequate low level of scattering is achieved. The ARSMS combines proprietary camera software with data analysis software and control software to achieve fully automatic operation with graphical user interfaces. This article presents the instrument concept and examples of the output. Device mapping in all degrees of freedom is shown to be better than 0.5 mm, with scattering sensitivity better than 0.5 ppm/cm. This system is able to scan and map the Rayleigh scattering of large samples in both of cylindrical and rectangular samples using cylindrical and Cartesian coordinates. [ABSTRACT FROM AUTHOR]

We develop a temporal simulation of the potentially detectable gravitational wave background from neutron star formation at cosmological distances. By using a recent model for the evolving star formation rate, we investigate the statistical distribution of gravitational wave amplitudes due to supernovae that result in neutron star formation in the Einstein–de Sitter cosmology. We find that the gravitational wave amplitude distribution in our frame is highly skewed, with skewness related to the distribution of sources, and that the potentially detectable gravitational wave strain is dominated by sources at a redshift of . Time traces of the simulation, using selected waveforms, are presented graphically and are also made available as web-based audio files. The method developed can readily be extended to different cosmologies, as well as to incorporate other waveforms and source types. This type of simulation will be useful in testing and optimizing detection strategies for gravitational wave backgrounds due to various types of individually undetectable astrophysical sources. [ABSTRACT FROM AUTHOR]

In this paper it is shown that although strong evidence exists for the evolution of intelligent life throughout our galaxy, attempts at detecting radio transmissions from extraterrestrial civilizations are doomed to failure unless technological civilizations can exist for periods of the order of 1 million years. If evolving technological civilizations are so driven by aggressive instinctual behaviour that they self‐destruct in 100–1000 years, then the number of co‐existing civilizations is too small for there to be a significant chance of detection. The outcome of the current vigorous search for extraterrestrial intelligence therefore has great significance to our own world‐view when faced with the threat of nuclear war. [ABSTRACT FROM PUBLISHER]

The methodology for accurately calibrating the Niobe resonant-mass gravitational wave detector is presented. The transducer is based on a low noise resonant microwave cavity transducer that converts the displacement of the resonating mass to microwave energy. The calibration technique consists of a one off measurement of the microwave frequency versus resonant-mass displacement characteristic. To measure this accurately, known static forces were applied to the resonant mass and the change in the transducer microwave frequency was recorded. With the aid of finite element analysis and accurate measurements of the resonant-mass characteristics, the deflection due to the known force was calculated. The calculated deflections were verified coarsely with measurements from a calibrated linear variable differential transformer. Typically, the detector operates with a 1 mK noise temperature. A best noise temperature of 890 μK between 1300 and 2000 Universal Time Coordinate (UTC) for day 60 in 1997 is reported. The transducer has been upgraded with a new microwave amplifier, which has a measured electronic noise floor 40 dB lower than the previous amplifier, which is only 10 dB above the quantum limit. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]