Strength of hydroxide catalysis bonds between sapphire, silicon, and fused silica as a function of time

Hydroxide catalysis bonds have formed an integral part of ground-based gravitational wave (GW) observatories since the 1990s. By allowing the creation of quasimonolithic fused silica mirror suspensions in detectors such as GEO600 and Advanced LIGO, their use was crucial to the first ever direct detection of gravitational waves. Following these successes, this bonding technique has been included in advanced next generation cryogenic detector designs. Currently, they are used to create quasimonolithic crystalline sapphire suspensions in the KAGRA detector. They are also planned for use in silicon suspensions of future detectors such as the Einstein Telescope. In this paper we report how the strength of hydroxide catalysis bonds evolves over time, and compare the curing rates of bonds as they form between fused silica substrates to those between sapphire to sapphire and silicon to silicon substrates. For bonds between all three types of substrate material we show that newly formed bonds exhibit slightly higher breaking stresses than bonds cured for longer periods of time. We find that the strength stabilizes at ≥ 15     MPa for bonds cured for up to 30 weeks (7 months). This finding is important to future cryogenic GW detector design as it is crucial to ensure the long term integrity of the suspension interfaces. Monitoring the strength of bonds that have been allowed to cure for shorter lengths of time can also shed light on the chemistry of bond formation

Indium joints for cryogenic gravitational wave detectors

A viable technique for the preparation of highly thermal conductive joints between sapphire components in gravitational wave detectors is presented. The mechanical loss of such a joint was determined to be as low as 2 × 10−3 at 20 K and 2 × 10−2 at 300 K. The thermal noise performance of a typical joint is compared to the requirements of the Japanese gravitational wave detector, KAGRA. It is shown that using such an indium joint in the suspension system allows it to operate with low thermal noise. Additionally, results on the maximum amount of heat which can be extracted via indium joints are presented. It is found that sapphire parts, joined by means of indium, are able to remove the residual heat load in the mirrors of KAGRA

Search for gravitational-lensing signatures in the full third observing run of the LIGO-Virgo network

Gravitational lensing by massive objects along the line of sight to the source causes distortions of gravitational wave-signals; such distortions may reveal information about fundamental physics, cosmology and astrophysics. In this work, we have extended the search for lensing signatures to all binary black hole events from the third observing run of the LIGO--Virgo network. We search for repeated signals from strong lensing by 1) performing targeted searches for subthreshold signals, 2) calculating the degree of overlap amongst the intrinsic parameters and sky location of pairs of signals, 3) comparing the similarities of the spectrograms amongst pairs of signals, and 4) performing dual-signal Bayesian analysis that takes into account selection effects and astrophysical knowledge. We also search for distortions to the gravitational waveform caused by 1) frequency-independent phase shifts in strongly lensed images, and 2) frequency-dependent modulation of the amplitude and phase due to point masses. None of these searches yields significant evidence for lensing. Finally, we use the non-detection of gravitational-wave lensing to constrain the lensing rate based on the latest merger-rate estimates and the fraction of dark matter composed of compact objects

Search for eccentric black hole coalescences during the third observing run of LIGO and Virgo

Despite the growing number of confident binary black hole coalescences observed through gravitational waves so far, the astrophysical origin of these binaries remains uncertain. Orbital eccentricity is one of the clearest tracers of binary formation channels. Identifying binary eccentricity, however, remains challenging due to the limited availability of gravitational waveforms that include effects of eccentricity. Here, we present observational results for a waveform-independent search sensitive to eccentric black hole coalescences, covering the third observing run (O3) of the LIGO and Virgo detectors. We identified no new high-significance candidates beyond those that were already identified with searches focusing on quasi-circular binaries. We determine the sensitivity of our search to high-mass (total mass M>70 M⊙) binaries covering eccentricities up to 0.3 at 15 Hz orbital frequency, and use this to compare model predictions to search results. Assuming all detections are indeed quasi-circular, for our fiducial population model, we place an upper limit for the merger rate density of high-mass binaries with eccentricities 0<e≤0.3 at 0.33 Gpc−3 yr−1 at 90\% confidence level

Ultralight vector dark matter search using data from the KAGRA O3GK run

Among the various candidates for dark matter (DM), ultralight vector DM can be probed by laser interferometric gravitational wave detectors through the measurement of oscillating length changes in the arm cavities. In this context, KAGRA has a unique feature due to differing compositions of its mirrors, enhancing the signal of vector DM in the length change in the auxiliary channels. Here we present the result of a search for U(1)B−L gauge boson DM using the KAGRA data from auxiliary length channels during the first joint observation run together with GEO600. By applying our search pipeline, which takes into account the stochastic nature of ultralight DM, upper bounds on the coupling strength between the U(1)B−L gauge boson and ordinary matter are obtained for a range of DM masses. While our constraints are less stringent than those derived from previous experiments, this study demonstrates the applicability of our method to the lower-mass vector DM search, which is made difficult in this measurement by the short observation time compared to the auto-correlation time scale of DM

Temperature dependence of the thermal conductivity of hydroxide catalysis bonds between silicon substrates

Measured thermal conductivity of hydroxide catalysis bonded silicon sample

Temperature dependence of the thermal conductivity of hydroxide catalysis bonds between silicon substrates

Future generations of gravitational wave detectors plan to use cryogenics in order to further reduce thermal noise associated with the mirror test masses and their suspensions. It is important that the thermal conductivity of candidate materials for these mirror suspension systems, and any additional thermal resistance associated with the required bonding/jointing, is characterised. Results are presented here for composite single-crystal silicon substrates, with multiple hydroxide catalysis bonds present, in order to assess the thermal conductivity of the bond layers. An average bond thickness of 460 nm is observed within the oxide-bond-oxide interfaces, with a calculated thermal conductivity rising from 0.013 → 0.087 Wm−1K −1 across a temperature range of 9 → 300 K. This confirms that the thermal conductance through hydroxide catalysis bonds, with geometries being considered for third generation gravitational wave detectors operating at 20 K or 125 K, would have a negligible impact on the required heat extraction for cryogenic operation. Therefore, the use of hydroxide catalysis bonding, as successfully demonstrated within room temperature gravitational wave detectors, remains an attractive solution for building future cryogenic instruments with reduced thermal noise and enhanced astrophysical reach

Open data from the first and second observing runs of Advanced LIGO and Advanced Virgo

Advanced LIGO and Advanced Virgo are monitoring the sky and collecting gravitational-wave strain data with sufficient sensitivity to detect signals routinely. In this paper we describe the data recorded by these instruments during their first and second observing runs. The main data products are gravitational-wave strain time series sampled at 16384 Hz. The datasets that include this strain measurement can be freely accessed through the Gravitational Wave Open Science Center at http://gw-openscience.org, together with data-quality information essential for the analysis of LIGO and Virgo data, documentation, tutorials, and supporting software