Generation Of Gravitational Wave Detectors Research Articles

Frequency-doubling of continuous laser light in the Laguerre–Gaussian modes LG0,0 and LG3,3

For future generations of gravitational wave detectors, it is proposed to use the helical Laguerre-Gaussian LG3,3 mode to reduce thermal noise, which limits the detector sensitivity. At the same time, this requires the efficient generation of squeezed vacuum states in the LG3,3 mode for quantum noise reduction. Since this technique includes the process of second harmonic generation (SHG), we experimentally compare the conversion efficiency and harmonic output field of the LG0,0 and LG3,3 modes in a cavity-enhanced SHG using the same 7% doped MgO:LiNbO3 crystal. Conversion efficiencies of 96% and 45% are achieved, respectively. The influence of mode mismatches and astigmatism is analyzed to estimate the ratio of the pump mode-dependent effective nonlinearities to be d0,0/d3,3∼5. Furthermore, we show that absorption loss in the crystal is more relevant for the LG3,3 mode.

Low phase noise squeezed vacuum for future generation gravitational wave detectors

Squeezed light has become a standard technique to enhance the sensitivity of gravitational wave detectors. Both optical losses and phase noise in the squeezed path can degrade the achievable improvements. Phase noise can be mitigated by having a high bandwidth servo to stabilize the squeezer phase to the light from the interferometer. In advanced LIGO, this control loop bandwidth is limited by the 4 km arm cavity free spectral range to about ∼15 kHz. Future generation gravitational-wave detectors are designed to employ much longer arm cavities. For cosmic explorer [], a 40 km arm length will limit the bandwidth to ∼1.5 kHz. We propose an alternative controls scheme that will increase the overall phase noise suppression by using the in-vacuum filter cavity as a reference for stabilizing the laser frequency of the squeezed light source. This will allow for rms phase noise of less than a milliradian—a negligible level for all future generations of gravitational-wave detectors [].

Distinguishing primordial black holes from astrophysical black holes by Einstein Telescope and Cosmic Explorer

We investigate how the next generation gravitational-wave (GW) detectors, such as Einstein Telescope (ET) and Cosmic Explorer (CE), can be used to distinguish primordial black holes (PBHs) from astrophysical black holes (ABHs). Since a direct detection of sub-solar mass black holes can be taken as the smoking gun for PBHs, we estimate the detectable limits of the abundance of sub-solar mass PBHs in cold dark matter by the targeted search for sub-solar mass PBH binaries and binaries containing a sub-solar mass PBH and a super-solar mass PBH, respectively. On the other hand, according to the different redshift evolutions of the merger rate for PBH binaries and ABH binaries, we forecast the detectable event rate distributions for the PBH binaries and ABH binaries by ET and CE respectively, which can serve as a method to distinguish super-solar mass PBHs from ABHs.

Exploring Populations of Low Mass Merging Compact Binary Systems with Single Einstein Telescope

AbstractEinstein Telescope (ET), a the future third generation gravitational wave detector will be sensitive to gravitational wave signal down to 1 Hz. We present an algorithm to estimate the parameters of the low mass merging compact binary systems such as localisation, chirp mass, redshift, mass ratios and total mass of the source which are crucial in order to estimate the capability of ET to study various compact binary populations. We analysed the compact binary populations of (i) Pop I and Pop II, (ii) Pop III, and (iii) globular clusters, with single ET.

Gravitomagnetic tidal resonance in neutron-star binary inspirals

A compact binary system implicating at least one rotating neutron star undergoes gravitomagnetic tidal resonances as it inspirals toward its final merger. These have a dynamical impact on the phasing of the emitted gravitational waves. The resonances are produced by the inertial modes of vibration of the rotating star. Four distinct modes are involved, and the resonances occur within the frequency band of interferometric gravitational-wave detectors when the star spins at a frequency that lies within this band. The resonances are driven by the gravitomagnetic tidal field created by the companion star; this is described by a post-Newtonian vector potential, which is produced by the mass currents associated with the orbital motion. These resonances were identified previously by Flanagan and Racine [Phys. Rev. D 75, 044001 (2007)], but these authors accounted only for the response of a single mode, the r-mode, a special case of inertial modes. All four relevant modes are included in the analysis presented in this paper. The total accumulated gravitational-wave phase shift is shown to range from approximately $10^{-2}$ radians when the spin and orbital angular momenta are aligned, to approximately $10^{-1}$ radians when they are anti-aligned. Such phase shifts will become measurable in the coming decades with the deployment of the next generation of gravitational-wave detectors (Cosmic Explorer, Einstein Telescope); they might even come to light within this decade, thanks to planned improvements in the current detectors. With good constraints on the binary masses and spins gathered from the inspiral waveform, the phase shifts deliver information regarding the internal structure of the rotating neutron star, and therefore on the equation of state of nuclear matter.

Sensitivity of the lower edge of the pair-instability black hole mass gap to the treatment of time-dependent convection

ABSTRACT Gravitational-wave detections are now probing the black hole (BH) mass distribution, including the predicted pair-instability mass gap. These data require robust quantitative predictions, which are challenging to obtain. The most massive BH progenitors experience episodic mass ejections on time-scales shorter than the convective turnover time-scale. This invalidates the steady-state assumption on which the classic mixing length theory relies. We compare the final BH masses computed with two different versions of the stellar evolutionary code $\tt{MESA}$: (i) using the default implementation of Paxton et al. (2018) and (ii) solving an additional equation accounting for the time-scale for convective deceleration. In the second grid, where stronger convection develops during the pulses and carries part of the energy, we find weaker pulses. This leads to lower amounts of mass being ejected and thus higher final BH masses of up to ∼$5\, \mathrm{M}_\odot$. The differences are much smaller for the progenitors that determine the maximum mass of BHs below the gap. This prediction is robust at $M_{\rm BH, max}\simeq 48\, \mathrm{M}_\odot$, at least within the idealized context of this study. This is an encouraging indication that current models are robust enough for comparison with the present-day gravitational-wave detections. However, the large differences between individual models emphasize the importance of improving the treatment of convection in stellar models, especially in the light of the data anticipated from the third generation of gravitational-wave detectors.

Gravitational waves and the Sagnac effect**This paper is dedicated to the memory of my late father Werner Frauendiener.

Light propagating in opposite directions around the same loop in general shows a relative phase shift when recombined. This phenomenon is known as the Sagnac effect after Georges Sagnac who, in 1913, demonstrated with an interferometer on a rotating table that the phase shift depended on the angular velocity of the table. In previous work we have given a very general formula for the Sagnac effect, valid in full general relativity. The relativistic effect not only contains the ‘classical’ contribution from the rotation of the laboratory but also contributions due its acceleration and due to incoming gravitational waves. Here, we point out a major consequence of this gravitational effect which may have implications for third generation gravitational wave detectors. We describe ‘antenna’ designs which pick out specific components of the Weyl tensor describing the incident gravitational waves.

Observing cosmological binary mergers with next generation neutrino and gravitational wave detectors

We discuss the potential of detecting thermal neutrinos from matter-rich binary mergers, via a decades-long multi-messenger campaign involving a Mt-scale water Cherenkov neutrino detector and one or more next generation gravitational wave detectors, capable of observing mergers up to redshift $z\sim 2$. The search of neutrinos in time-coincidence with gravitational wave detections will allow to identify single neutrinos from individual mergers above the background, and to study their distributions in energy, redshift and type (double neutron-star or neutron-star-black hole merger) of the candidate sources. We find that, for merger rates consistent with current LIGO-Virgo constraints, and for a $100~{\rm Mt\cdot yr}$ exposure, between ${\mathcal O(10^{-1})}$ and ${\mathcal O(10)}$ neutrino events are expected. For extreme cases of mergers with more than $10^{52}$ ergs emitted in $\mathrel{{\bar \nu}_e}$, the number of events can be as large as $\sim 100$, with sensitivity to mergers up to redshift $z\sim 0.5$ or so. Such scenarios can already be tested with a $10~{\rm Mt\cdot yr}$ exposure, resulting in constraints on the post-merger evolution of the systems being considered.

High power, single-frequency, monolithic fiber amplifier for the next generation of gravitational wave detectors.

Low noise, high power single-frequency lasers and amplifiers are key components of interferometric gravitational wave detectors. One way to increase the detector sensitivity is to increase the power injected into the interferometers. We developed a fiber amplifier engineering prototype with a pump power limited output power of 200 W at 1064 nm. No signs of stimulated Brillouin scattering are observed at 200 W. At the maximum output power the polarization extinction ratio is above 19 dB and the fractional power in the fundamental transverse mode (TEM 00) was measured to be 94.8 %. In addition, measurements of the frequency noise, relative power noise, and relative pointing noise were performed and demonstrate excellent low noise properties over the entire output power slope. In the context of single-frequency fiber amplifiers, the measured relative pointing noise below 100 Hz and the higher order mode content is, to the best of our knowledge, at 200 W the lowest ever measured. A long-term test of more than 695 h demonstrated stable operation without beam quality degradation. It is also the longest single-frequency fiber amplifier operation at 200 W ever reported.

Modeling the postmerger gravitational wave signal and extracting binary properties from future binary neutron star detections

Gravitational wave astronomy has established its role in measuring the equation of state governing cold supranuclear matter. To date and in the near future, gravitational wave measurements from neutron star binaries are likely to be restricted to the inspiral. However, future upgrades and the next generation of gravitational wave detectors will enable us to detect the gravitational wave signatures emitted after the merger of two stars, at times when densities beyond those in single neutron stars are reached. Therefore, the postmerger gravitational wave signal enables studies of supranuclear matter at its extreme limit. To support this line of research, we present new and updated phenomenological relations between the binary properties and characteristic features of the postmerger evolution. Most notably, we derive an updated relation connecting the mass-weighted tidal deformability and the maximum neutron star mass to the dominant emission frequency of the postmerger spectrum. With the help of a configuration-independent Bayesian analysis using simplified Lorentzian model functions, we find that the main emission frequency of the postmerger remnant, for signal-to-noise ratios of $8$ and above, can be extracted within a 1-sigma uncertainty of about 100 Hz for Advanced LIGO and Advanced Virgo's design sensitivities. In some cases, even a postmerger signal-to-noise ratio of $4$ can be sufficient to determine the main emission frequency. This will enable us to measure binary and equation-of-state properties from the postmerger, to perform a consistency check between different parts of the binary neutron star coalescence, and to put our physical interpretation of neutron star mergers to the test.

Testing the multipole structure and conservative dynamics of compact binaries using gravitational wave observations: The spinning case

In an earlier work [S. Kastha et al., Phys. Rev. D 98, 124033 (2018)], we developed the parametrized multipolar gravitational wave phasing formula to test general relativity, for the nonspinning compact binaries in quasicircular orbit. In this paper, we extend the method and include the important effect of spins in the inspiral dynamics. Furthermore, we consider parametric scaling of post-Newtonian (PN) coefficients of the conserved energy for the compact binary, resulting in the parametrized phasing formula for nonprecessing spinning compact binaries in quasicircular orbit. We also compute the projected accuracies with which the second and third generation ground-based gravitational wave detector networks as well as the planned space-based detector LISA will be able to measure the multipole deformation parameters and the binding energy parameters. Based on different source configurations, we find that a network of third-generation detectors would have comparable ability to that of LISA in constraining the conservative and dissipative dynamics of the compact binary systems. This parametrized multipolar waveform would be extremely useful not only in deriving the first upper limits on any deviations of the multipole and the binding energy coefficients from general relativity using the gravitational wave detections, but also for science case studies of next generation gravitational wave detectors.

Phenomenological inclusion of alternative dispersion relations to the Teukolsky equation and its application to bounding the graviton mass with gravitational-wave measurements

Existing constraints on the graviton mass from gravitational-wave detections rely on the phase difference developed between different frequencies during the propagation. Effects on the quasinormal-mode frequencies of the black-hole ringdown due to the graviton mass are often ignored. While perturbation theories of black holes have been well developed in the context of general relativity, this is not the case for modified gravity theories. We propose a phenomenological modification to the Teukolsky equation of perturbed black holes to include the dispersion relation due to a gravitational field of nonzero mass. Solving this modified Teukolsky equation by logarithmic perturbation theory, we compute the shift of the quasinormal-mode frequencies due to the presence of a graviton mass. This hypothetical shift can be used to constrain the graviton mass with ringdown signals, either standalone or in conjunction with the phase difference accumulated due to the wave propagation. We estimate that constraints on the graviton mass of $m_g \lesssim 10^{-15}\,\textrm{eV}$ can be put with a detection of the ringdown signal alone by second generation gravitational-wave detectors.

Characteristics of surface wave Green’s function for anisotropic ambient seismic noise field — a case study in Limburg, The Netherlands

Abstract The Advanced LIGO and the Advanced Virgo gravitational wave (GW) detectors are built on the surface of the earth. Seismic noise being most dominant on the surface limits the low frequency sensitivity of the detectors below 10 Hz. The Einstein Telescope (ET), a European project for constructing a third generation GW detector aims to improve current detector sensitivity by an order of magnitude at frequencies below 10 Hz. One way of reducing the contribution from seismic noise is by building the detector underground. Currently seismic studies are being conducted in Sardinia, Italy and Limburg, The Netherlands, for selecting an appropriate site for constructing the ET. A dense array of 146 wireless vertical component geophones was deployed at Limburg in The Netherlands with the aim of performing passive seismic tomography using the seismic noise in the frequency band 2.5–8.0 Hz. Theoretically for accurate extraction of surface wave Green’s function, an isotropic distribution of noise sources surrounding a station pair is desired. However, in reality the distribution of noise sources manifest azimuthal anisotropy and also vary in source magnitude. In this article, we discuss the results of the accuracy of the extracted surface wave Green’s function when illuminated by an anisotropic distribution of noise sources. We make use of the method of cross-correlation beamforming to extract station pairs that yield accurate surface waves Green’s function and consequently compute the surface wave group velocities for the region.

Astrophysics with core-collapse supernova gravitational wave signals in the next generation of gravitational wave detectors

The next generation of gravitational wave detectors will improve the detection prospects for gravitational waves from core-collapse supernovae. The complex astrophysics involved in core-collapse supernovae pose a significant challenge to modeling such phenomena. The Supernova Model Evidence Extractor (SMEE) attempts to capture the main features of gravitational wave signals from core-collapse supernovae by using numerical relativity waveforms to create approximate models. These models can then be used to perform Bayesian model selection to determine if the targeted astrophysical feature is present in the gravitational wave signal. In this paper, we extend SMEE's model selection capabilities to include features in the gravitational wave signal that are associated with g-modes and the standing accretion shock instability. For the first time, we test SMEE's performance using simulated data for planned future detectors, such as the Einstein Telescope, Cosmic Explorer, and LIGO Voyager. Further to this, we show how the performance of SMEE is improved by creating models from the spectrograms of supernova waveforms instead of their timeseries waveforms that contain stochastic features. In third generation detector configurations, we find that about 50% of neutrino-driven simulations were detectable at 100 kpc, and 10% at 275 kpc. The explosion mechanism was correctly determined for all detected signals.

A multistage vibration isolation system for Advanced Virgo suspended optical benches

We present a compact, vacuum compatible seismic attenuation system designed to isolate five auxiliary optical benches for Advanced Virgo, a second generation gravitational wave detector. We report on the design of the device, coined MultiSAS (multistage seismic attenuation system) and on its measured vibration isolation performance. The latter can be summarized by quoting a payload isolation ratio at 10 Hz of 100 dB and 140 dB in vertical and horizontal, respectively. We also present the design and performance of the MultiSAS control system along the translation degrees of freedom, as well as a discussion of the possible coupling to the angular degrees of freedom. Over a time-scale of 100 s, 1 m magnitude RMS for translational degrees of freedom is achieved for seismic conditions observed in the past five years at the Virgo site and in Amsterdam. The spectral displacement levels are expected to be lower than 10−14 m from 10 Hz onwards in vertical and horizontal. In addition we discuss effects that could deteriorate the performance of the device such as thermal drifts of the mechanical filters, residual acoustic coupling and cradle effects on the inverted pendulum pre-isolation stage. Mitigation strategies or solutions were devised and installed in the five Advanced Virgo systems.

Probing the Fermi-LAT GeV Excess with Gravitational Waves.

If the gamma-ray excess towards the inner Galaxy (GCE) detected in Fermi-LAT data is due to millisecond pulsars (MSPs), one expects an associated gravitational wave (GW) signal, whose intensity exceeds the disk MSP population emission by an order of magnitude. We compute the expected GW counterpart of the bulge MSP population based on fits of the GCE, and estimate the sensitivity reach of current and future terrestrial GW detectors. The bounds on the average population ellipticity ϵ are competitive with the existing ones derived by LIGO/Virgo towards known MSPs. With a 10-yr data taking in current LIGO/Virgo configuration, one would detect a signal at the level ϵ≃10^{-7}, while ϵ≃10^{-8} would be attainable with a similar data taking period with a third generation GW detector. This sensitivity should be sufficient for crucial diagnostics on the GCE interpretation in terms of MSPs.

Nd:YVO4 high-power master oscillator power amplifier laser system for second-generation gravitational wave detectors.

Ultrastable high-power laser systems are essential components of the long baseline interferometers that detected the first gravitational waves from merging black holes and neutron stars. One way to further increase the sensitivity of current generation gravitational wave detectors (GWDs) is to increase the laser power injected into the interferometers. In this Letter, we describe and characterize a 72 W and a 114 W linearly polarized, single-frequency laser system at a wavelength of 1064 nm, each based on single-pass Nd:YVO4 power amplifiers. Both systems have low power and frequency noise and very high spatial purity with less than 10.7% and 2.9% higher order mode content, respectively. We demonstrate the simple integration of these amplifiers into the laser stabilization environment of operating GWDs and show stable low-noise operation of one of the amplifier systems in such an environment for more than 45 days.

Reduction in internal friction in silica glass with high OH content

AbstractThe aim of this article was to investigate processes occurring during annealing of silica glass classified as being of type III (J Non Cryst Solids. 1970;5(2):123‐75). This is an inexpensive silica glass produced by many manufacturers across the globe. However, it can be successfully used for fabrication of high‐Q mechanical resonators. The relationship between residual internal stress and internal friction is elucidated. Quantitative analysis of the structural relaxation kinetics is presented. The influence of the cooling process for structural transformation is also discussed. On the basis of our results, we suggest optimal annealing conditions for minimizing internal friction type III silica glass. The results will be useful for further improvement of the Q‐factor of mechanical resonators, including the test masses of the next generation of gravitational wave detectors. Our approach might, in addition, be used for studying the modification of atomic structure in multicomponent glasses.

Hidden-sector modifications to gravitational waves from binary inspirals

Gravitational wave astronomy has placed strong constraints on fundamental physics, and there is every expectation that future observations will continue to do so. In this work we quantify this expectation for future binary merger observations to constrain hidden sectors, such as scalar-tensor gravity or dark matter, which induce a Yukawa-type modification to the gravitational potential. We explicitly compute the gravitational waveform, and perform a Fisher information matrix analysis to estimate the sensitivity of next generation gravitational wave detectors to these modifications. We find an optimal sensitivity to the Yukawa interaction strength of 10−5 and to the associated dipole emission parameter of 10−7, with the best constraints arising from the Einstein telescope. When applied to a minimal model of dark matter, this provides an exquisite probe of dark matter accumulation by neutron stars, and for sub-TeV dark matter gravitational waves are able to detect mass fractions less then 1 part in 1015.

Modular suspension system with low acoustic coupling to the suspended test mass in a prototype gravitational wave detector.

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.