Heating elements surrounding the core optics of Gravitational Wave Interferometer are used to correct the radius of curvature of the high reflectivity surface that can deviate from the nominal value because of manufacturing defects and the non-zero absorption of the laser power in the substrate and in the coatings of the test masses. The typical actuation time of these actuators (usually...
The Einstein Telescope (ET) is a third generation gravitational wave observatory, currently in the planning stage in Europe. The ET project involves the construction of a triangular shape underground facility with 10 kilometres long arms buried in ca. 250 m depth. At the corner points, large caverns host the required infrastructure. The border region between the Netherlands, Belgium and...
The anelastic behavior of amorphous materials is explained by the presence of two level systems, metastable states that are separated by an energy barrier.
Not all the TLS contribute to the mechanical losses. The ones that are active are only those with a relaxation time comparable to the period T of the strain wave propagating in the material. In order to reduce the dissipation in the...
In the design studies of the next-generation gravitational wave detectors, coating Brownian thermal noise is a major noise contribution at frequencies around 100Hz. One proposed method to mitigate this noise source is to use a higher-order laser mode instead of the currently used fundamental Gaussian mode because their more uniform intensity distributions could average better over the mirror...
Cryogenic gravitational wave detectors are planned to be significantly more sensitive than current room temperature detectors. Cryogenic detection relies on materials that have low mechanical loss and Brownian noise at low temperatures, ruling out the use of the fused silica mirrors currently used. Silicon is proposed as a cryogenic mirror substrate due to its excellent mechanical loss and...
The four sapphire mirrors in KAGRA will be cooled down to 20K to reduce thermal noise. We selected substrates with the lowest thermal absorption for the input mirrors. As for birefringence, we conducted an X-ray analysis to determine the direction of the crystal axis so that the effect of birefringence on to the laser beam is negligible. However, when we operated the interferometer with the...
The Einstein Telescope (ET) is an advanced, third generation gravitational wave observatory, currently in the planning stage in Europe. The ET project involves construction of a triangular shape underground facility with 10 kilometres long arms. The border region between the Netherlands, Belgium and Germany is considered as a potential location and will be further investigated in a feasibility...
To successfully integrate cryocooled optics in the complex system of future gravitational wave detectors, it is mandatory that cryogenics is compliant with the operative methods adopted to properly control and possibly mitigate all noise sources. Among others, electrostatic charging on test mass has been shown to be a limiting noise source for gravitational wave interferometers. Within the...
The wavelength of 2um is a candidate for the next generation gravitational-wave detectors such as LIGO Voyager and Einstein Telescope. Although the technical leap of the wavelength change impacts almost all the optical components of laser interferometry, only a few investigations have been ongoing. This poster will present the R&D experiments planned in the Gravitational Exploration Institute,...
All gravitational-wave observatories (GWOs) have been using the laser wavelength of 1064 nm. Ultra-stable laser devices are at the sites of GEO 600, Kagra, LIGO and Virgo. Since 2019, not only GEO 600 but also LIGO and Virgo have been using separate devices for squeezing the uncertainty of the light, so-called squeeze lasers. The sensitivities of future GWOs will strongly gain from reducing...
Cryogenic suspensions are subjected to a number of conflicting requirements.
An idea replacing the suspension fibers with massive beams is presented here to suspend the mirrors while attempting to solve these constraints.
The powerful beams stored in the Fabry Perot cavities of gravitational wave detectors deposit heat on the mirror coatings and cause thermal lensing. We present an experiment that studies the feasibility to balance that excess heat by selectively absorbing the black body heat that at ambient temperature naturally radiates from the test masses. It is shown how the coating heating effect can be...
Gravitational forces that oscillate at audio-band frequencies are measured with masses suspended as pendulums that have resonance frequencies even lower.
If the pendulum is excited by thermal energy or by seismic motion of the environment, the measurement sensitivity is reduced.
Conventionally, this problem is mitigated by seismic isolation and linear damping, potentially combined with...
A factor of two in coating thermal noise reduction is required to achieve the design sensitivity of Advanced LIGO+. For ET-HF and the initial Cosmic Explorer design very similar coating thermal noise levels are assumed. Low optical absorption of the coatings of <1ppm is also required, but challenging to meet.
Multimaterial designs allow for a trade-off between thermal noise and absorption,...
As improvements to the current gravitational wave detector network are implemented, and as new detectors are added to the network, any new mirror coating designs must overcome the twofold challenge of producing sufficiently lower thermal noise perfomance, as well as maintaining a low level of optical absorption. Here we present an update on our research into characterizing the room...
Advanced gravitational waves detectors revealed until now a significant number of signals from the mergers of compact objects with amplitudes of the order of 10^(-21)-10^(-22). The necessity to increase the detection volume and the number of candidate sources requires an improvement of the sensitivity of the interferometers (ITF). For this purpose, an increase of laser power in the ITF and...
Advanced gravitational-wave detectors require low-loss Faraday isolators in the squeezer path, in order to maximize the benefits of the squeezed light injection. The University of Florida and Montclair State University have developed and are currently building two designs of low-loss Faraday isolators for the A+ upgrade, one output Faraday isolator (20 mm clear aperture) and two squeezer...
Gravitational wave detectors impose extremely stringent requirements for the optical and mechanical properties of their mirrors. Research in new coating material focuses on minimizing mechanical losses which directly relate to the coating thermal noise. At the same time, absorption and scattering losses need to be kept at extremely low levels, since they strongly affect the operation and...
While gravitational waves are regularly detected in several gravitational wave detectors globally, the research endeavors to improve the sensitivity of these detectors continues. Low mechanical loss and low optical absorption are key requirements of future coatings. Amorphous silicon has very low loss but relatively high absorption at the relevant wavelengths. Crystalline silicon also has low...
Authors: V. Spagnuolo, S. Gouvalas, I.W. Martin, G. McGhee, P. Murray, S. Tait, C. Clark, S. Hild, and J. Steinlechner
For current gravitational wave interferometers, the limit in sensitivity at their most sensitive frequencies originates from the combination of thermal noise and quantum noise. The main contribution to the thermal noise arises from the Brownian motion of high reflectivity...
Sources of geophysical and anthropogenic noise, such as wind, sea activity, earthquakes, local traffic, etc., can impact gravitational wave interferometers by causing sensitivity drops and lock losses. During the 1-year long O3 observation run, the Virgo Collaboration collected a statistically significant amount of data to study the response of the detector to a variety of environmental...
Suspension thermal noise is a significant noise source for torsion pendulums. Two ways to reduce it is to utilize cryogenic temperatures and crystalline fibres. We record our progress here in utilising both in tandem to achieve low suspension noise levels, with an eye on achieving high Q for use in TOrsion Bar Antenna (TOBA), a proposed gravitational wave detector aimed at 0.1-10 Hz
Future gravitational wave detectors plan to operate at cryogenic temperatures using crystalline silicon test masses which are transparent at higher wavelengths of light. Here we present measurements of a multi-material coating design that uses layers of ion-plated tantala, silica and amorphous silicon to reduce coating thermal noise and produce low optical absorption at low temperatures. Here...
Thermo-optic noise is one of the possible sources of coating thermal noise that affects precision optical measurements, such as gravitational-wave detectors. A lot of effort is dedicated to identify coatings with low Brownian noise, but also coating thermo-optic noise should be considered as a possible limiting noise source for the next generation of GWDs mirrors. SiNx is one of the most...
A signal-recycling Michaelson interferometer with an optical parametric amplification (OPA) has a large potential for a high-frequency gravitational-wave detection. The OPA using a nonlinear crystal in the signal-recycling cavity amplifies the signal and makes a stiff optical spring. A number of degrees of freedom need to be controlled to stabilize the system. Using a digital signal-processing...
The sensitivity of second-generation gravitational-wave detectors is limited in the low frequency region by Newtonian noise. Noise cancellation using Wiener filters has been shown to mitigate the effects of seismic Newtonian noise. This involves placing an array of seismometers around the test mass to monitor the ground fluctuations. Optimal positioning of the seismometers around the test mass...
In interferometric gravitational wave detectors, thermal noise from the mirrors, originating from mechanical dissipation in the coating films, represents the major limitation to sensitivity. Significant experimental effort has led to improvements during these years and currently the most advanced technology is the one of amorphous coatings. Yet, there is still a lack of understanding of the...
