The second-generation of gravitational-wave detectors are just starting operation, and have already yielding their first detections. Research is now concentrated on how to maximize the scientific potential of gravitational-wave astronomy. To support this effort, we present here design targets for a new generation of detectors, which will be capable of observing compact binary sources with high signal-to-noise ratio throughout the Universe.
This paper reviews some of the key enabling technologies for advanced and future laser interferometer gravitational wave detectors, which must combine test masses with the lowest possible optical and acoustic losses, with high stability lasers and various techniques for suppressing noise. Sect. 1 of this paper presents a review of the acoustic properties of test masses. Sect. 2 reviews the technology of the amorphous dielectric coatings which are currently universally used for the mirrors in advanced laser interferometers, but for which lower acoustic loss would be very advantageous. In sect. 3 a new generation of crystalline optical coatings that offer a substantial reduction in thermal noise is reviewed. The optical properties of test masses are reviewed in sect. 4, with special focus on the properties of silicon, an important candidate material for future detectors. Sect. 5 of this paper presents the very low noise, high stability laser technology that underpins all advanced and next generation laser interferometers.
This work characterises the sky localization and early warning performance of networks of third generation gravitational wave detectors, consisting of different combinations of detectors with either the Einstein Telescope or Cosmic Explorer configuration in sites in North America, Europe and Australia. Using a Fisher matrix method which includes the effect of earth rotation, we estimate the sky localization uncertainty for $1.4text{M}odot$-$1.4text{M}odot$ binary neutron star mergers at distances $40text{Mpc}$, $200text{Mpc}$, $400text{Mpc}$, $800text{Mpc}$, $1600text{Mpc}$, and an assumed astrophysical population up to redshift of 2 to characterize its performance for binary neutron star observations. We find that, for binary neutron star mergers at $200text{Mpc}$ and a network consisting of the Einstein Telescope, Cosmic Explorer and an extra Einstein Telescope-like detector in Australia(2ET1CE), the upper limit of the size of the 90% credible region for the best localized 90% signals is $0.51text{deg}^2$. For the simulated astrophysical distribution, this upper limit is $183.58text{deg}^2$. If the Einstein Telescope-like detector in Australia is replaced with a Cosmic Explorer-like detector(1ET2CE), for $200text{Mpc}$ case, the upper limit is $0.36text{deg}^2$, while for astrophysical distribution, it is $113.55text{deg}^2$. We note that the 1ET2CE network can detect 7.2% more of the simulated astrophysical population than the 2ET1CE network. In terms of early warning performance, we find that a network of 2ET1CE and 1ET2CE networks can both provide early warnings of the order of 1 hour prior to merger with sky localization uncertainties of 30 square degrees or less. Our study concludes that the 1ET2CE network is a good compromise between binary neutron stars detection rate, sky localization and early warning capabilities.
The second generation of gravitational-wave detectors are being built and tuned all over the world. The detection of signals from binary black holes is beginning to fulfill the promise of gravitational-wave astronomy. In this work, we examine several possible configurations for third-generation laser interferometers in existing km-scale facilities. We propose a set of astrophysically motivated metrics to evaluate detector performance. We measure the impact of detector design choices against these metrics, providing a quantitative cost-benefit analyses of the resulting scientific payoffs.
Future ground-based gravitational-wave detectors are slated to detect black hole and neutron star collisions from the entire stellar history of the universe. To achieve the designed detector sensitivities, frequency noise from the laser source must be reduced below the level achieved in current Advanced LIGO detectors. This paper reviews the laser frequency noise suppression scheme in Advanced LIGO, and quantifies the noise coupling to the gravitational-wave readout. The laser frequency noise incident on the current Advanced LIGO detectors is $8 times 10^{-5}~mathrm{Hz/sqrt{Hz}}$ at $1~mathrm{kHz}$. Future detectors will require even lower incident frequency noise levels to ensure this technical noise source does not limit sensitivity. The frequency noise requirement for a gravitational wave detector with arm lengths of $40~mathrm{km}$ is estimated to be $7 times 10^{-7}~mathrm{Hz/sqrt{Hz}}$. To reach this goal a new frequency noise suppression scheme is proposed, utilizing two input mode cleaner cavities, and the limits of this scheme are explored. Using this scheme the frequency noise requirement is met, even in pessimistic noise coupling scenarios.
In the next decade, new ground-based Cosmic Microwave Background (CMB) experiments such as Simons Observatory (SO), CCAT-prime, and CMB-S4 will increase the number of detectors observing the CMB by an order of magnitude or more, dramatically improving our understanding of cosmology and astrophysics. These projects will deploy receivers with as many as hundreds of thousands of transition edge sensor (TES) bolometers coupled to Superconducting Quantum Interference Device (SQUID)-based readout systems. It is well known that superconducting devices such as TESes and SQUIDs are sensitive to magnetic fields. However, the effects of magnetic fields on TESes are not easily predicted due to the complex behavior of the superconducting transition, which motivates direct measurements of the magnetic sensitivity of these devices. We present comparative four-lead measurements of the critical temperature versus applied magnetic field of AlMn TESes varying in geometry, doping, and leg length, including Advanced ACT (AdvACT) and POLARBEAR-2/Simons Array bolometers. Molybdenum-copper bilayer ACTPol TESes are also tested and are found to be more sensitive to magnetic fields than the AlMn devices. We present an observation of weak-link-like behavior in AlMn TESes at low critical currents. We also compare measurements of magnetic sensitivity for time division multiplexing SQUIDs and frequency division multiplexing microwave rf-SQUIDs. We discuss the implications of our measurements on the magnetic shielding required for future experiments that aim to map the CMB to near-fundamental limits.