Sapphire mirror for the KAGRA gravitational wave detector

Hirose, E.; Bajuk, Dan; Billingsley, G.; Kajita, T.; Kestner, Bob; Mio, Norikatsu; Ohashi, M.; Reichman, B.; Yamamoto, H.; Zhang, Liyuan

doi:10.1103/physrevd.89.062003

Cited by 37 publications

(33 citation statements)

References 12 publications

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“…Figure 4 shows the thermal noise strain curves from crystalline silicon test masses held at 123 K, where it can be seen that neither Brownian nor thermo-optic substrate noises should limit detector sensitivity. To justify this material and temperature choice, we compare its thermal noise performance with three other materials that are currently used or proposed for use in GW interferometers: fused silica [8,9], sapphire [10], and 10 K silicon [11]. Thermal noise in a fused silica test mass is limited by Brownian motion, which is related to mechanical loss through the fluctuation-dissipation theorem [12,13,14].…”

Section: Methodsmentioning

confidence: 99%

A cryogenic silicon interferometer for gravitational-wave detection

Adhikari¹,

Aguiar²,

Arai³

et al. 2020

Class. Quantum Grav.

183

110

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The detection of gravitational waves from compact binary mergers by LIGO has opened the era of gravitational wave astronomy, revealing a previously hidden side of the cosmos. To maximize the reach of the existing LIGO observatory facilities, we have designed a new instrument able to detect gravitational waves at distances 5 times further away than possible with Advanced LIGO, or at greater than 100 times the event rate. Observations with this new instrument will make possible dramatic steps toward understanding the physics of the nearby universe, as well as observing the universe out to cosmological distances by the detection of binary black hole coalescences. This article presents the instrument design and a quantitative analysis of the anticipated noise floor. • Quantum noise will be reduced by increasing the optical power stored in the arms. In Advanced LIGO, the stored power is limited by thermally induced wavefront distortion effects in the fused silica test masses. These effects will be alleviated by choosing a test mass material with a high thermal conductivity, such as silicon. • The test mass temperature will be lowered to 123 K, to mitigate thermo-elastic noise. This species of thermal noise is especially problematic in test masses ‡ 1/e 2 intensity § Round-trip loss; see section 5.2 (DRFPMI) with frequency dependent squeezed light injection. The beam from a 2µm prestabilized laser (PSL), passes through an input mode cleaner (IMC) and is injected into the DRFPMI via the power-recycling mirror (PRM). Signal bandwidth is shaped via the signal recycling mirror (SRM). A squeezed vacuum source (SQZ) injects this vacuum into the DRFPMI via an output Faraday isolator (OFI) after it is reflected off a filter-cavity to provide frequency dependent squeezing. A Faraday isolator (FCFI) facilitates this coupling to the filter cavity. The output from the DRFPMI is incident on a balanced homodyne detector, which employs two output mode cleaner cavities (OMC1 and OMC2) and the local oscillator light picked off from the DRFPMI. Cold shields surround the input and end test masses in both the X and Y arms (ITMX, ITMY, ETMX and ETMY) to maintain a temperature of 123 K in these optics. The high-reflectivity coatings of the test masses are made from amorphous silicon. detected (with SNR = 8) as a function of the total mass of the binary (in the source frame). (B) Donut visualization of the horizon distance of LIGO Voyager, aLIGO, and A+, shown with a population of binary neutron star mergers (yellow) and 30-30 M binary black hole mergers (gray). This assumes a Madau-Dickinson star formation rate [7] and a typical merger time of 100 Myr.

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Section: Methodsmentioning

confidence: 99%

A cryogenic silicon interferometer for gravitational-wave detection

Adhikari¹,

Aguiar²,

Arai³

et al. 2020

Class. Quantum Grav.

183

110

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“…The first sample has a size compliant with the KAGRA design, the second one is a smaller one and is used for additional measurements. Note that, compared to other similar measurement methods previously applied to sapphire substrates for the KAGRA interferometer 11 , we are here able to provide a three-dimensional picture of the absorption features of our samples. This approach is here proven to be especially useful because it provides a significant amount of information helping to establish the possible origins of the increased absorption.…”

Section: Discussionmentioning

confidence: 79%

3D characterization of low optical absorption structures in large crystalline sapphire substrates for gravitational wave detectors

Marchio

Leonardi

Bazzan

et al. 2021

Sci Rep

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Very high-quality sapphire substrates are key elements of the cryogenic Japanese gravitational interferometer KAGRA, in which they are used to build the main mirrors, working as the test masses to sense the gravitational waves. To meet the extreme requirements of this system, the sapphire test masses must possess an extremely low optical absorption, which makes their study challenging using standard methods. In this paper, we illustrate the results obtained on two typical samples using a specialized absorption setup based on the technique of Photo-thermal Common-path Interferometry (PCI). Our system combines a very high sensitivity to small absorption features with the possibility to perform a full three-dimensional mapping of the sample volume. Our results elucidate how the ultra-low absorption variations inside the sample possess a structure that is probably inherited from the growth history of the sample. Some conclusions on the role of structural defects as preferential sites for the inclusion of absorbing centers are drawn.

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“…For floating zone grown silicon, absorption as low as 5 ppm/cm has been measured but size is limited to about 10 cm diameter [124]. In the case of sapphire the best absorption is around 30 ppm/cm with sizes in the range of 20 cm diameter [125]. The bottom line is that, at present, an interferometer operated at low temperature will have to use smaller mirror compared to the 35 cm diameter fused silica mirrors that are used at room temperature.…”

Section: The Cryogenic Challengesmentioning

confidence: 97%

“…The sapphire crystals substrates will be 22 cm diameter and 15 cm thick. The polishing of a test sample has shown that is possible to achieve flatness rms below 1 nm as it is the case for fused silica substrates [125]. The most critical parameter is the absorption in the sapphire which is required to be 30 ppm/cm (the large crystals received so are about a factor of two above this value).…”

Section: The Kagra Solutionsmentioning

confidence: 99%

Gravitational wave astronomy: the current status

Blair

Zhao

et al. 2015

Sci. China Phys. Mech. Astron.

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In the centenary year of Einstein's General Theory of Relativity, this paper reviews the current status of gravitational wave astronomy across a spectrum which stretches from attohertz to kilohertz frequencies. Sect. 1 of this paper reviews the historical development of gravitational wave astronomy from Einstein's first prediction to our current understanding the spectrum. It is shown that detection of signals in the audio frequency spectrum can be expected very soon, and that a north-south pair of next generation detectors would provide large scientific benefits. Sect. 2 reviews the theory of gravitational waves and the principles of detection using laser interferometry. The state of the art Advanced LIGO detectors are then described. These detectors have a high chance of detecting the first events in the near future. Sect. 3 reviews the KAGRA detector currently under development in Japan, which will be the first laser interferometer detector to use cryogenic test masses. Sect. 4 of this paper reviews gravitational wave detection in the nanohertz frequency band using the technique of pulsar timing. Sect. 5 reviews the status of gravitational wave detection in the attohertz frequency band, detectable in the polarisation of the cosmic microwave background, and discusses the prospects for detection of primordial waves from the big bang. The techniques described in sects. 1-5 have already placed significant limits on the strength of gravitational wave sources. Sects. 6 and 7 review ambitious plans for future space based gravitational wave detectors in the millihertz frequency band. Sect. 6 presents a roadmap for development of space based gravitational wave detectors by China while sect. 7 discusses a key enabling technology for space interferometry known as time delay interferometry. gravitational waves, ground based detectors, pulsar timing, spaced based detectors, CMB PACS number(s): 04.80. Nn, 07.20.Mc,

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Sapphire mirror for the KAGRA gravitational wave detector

Cited by 37 publications

References 12 publications

A cryogenic silicon interferometer for gravitational-wave detection

A cryogenic silicon interferometer for gravitational-wave detection

3D characterization of low optical absorption structures in large crystalline sapphire substrates for gravitational wave detectors

Gravitational wave astronomy: the current status

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