E-TEST: a compact low-frequency isolator for a large cryogenic mirror

Abstract

To achieve the expected level of sensitivity of third-generation
gravitational-wave observatories, more accurate and sensitive instruments than those of the second generation must be used to reduce all sources of noise.
Amongst them, one of the most relevant is seismic noise, which will require the
development of a better isolation system, especially at low frequencies (below 10
Hz), the operation of large cryogenic silicon mirrors, and the improvement of
optical wavelength readouts. In this framework, this article presents the activities
of the E-TEST (Einstein Telescope Euregio Meuse-Rhine Site & Technology) to
develop and test new key technologies for the next generation of GW observatories.
A compact isolator system for a large silicon mirror at a low frequency is proposed. The design of the isolator allows the overall height
of the isolation system to be significantly compact and also suppresses seismic
noise at low frequencies. To minimize the effect of thermal noise, the isolation
system is provided with a 100-kg silicon mirror which is suspended in a vacuum
chamber at cryogenic temperature (25-40 K). To achieve this temperature without
inducing vibrations to the mirror, a radiation-based cooling strategy is employed.
In addition, cryogenic sensors and electronics are being developed as part of the
E-TEST to detect vibrational motion in the penultimate cryogenic stage. Since
the used silicon material is not transparent below the wavelengths
typically used for GW detectors, new optical components and
lasers must be developed in the range above 1500 nm to reduce absorption and
scattering losses. Therefore, solid-state and fiber lasers with a wavelength of 2090
nm, matching high-efficiency photodiodes, and low-noise crystalline coatings are
being developed. Accordingly, the key technologies provided by E-TEST serve
crucially to reduce the limitations of the current generation of GW observatories
and to determine the technical design for the next generation.


Dynamic coherence scanning interferometry based on an optical phase mask for simultaneous measurement of local induced vibration and local topology change of a mirror

“…The E-TEST demonstrator aims to prove the improvement in the stability of the GW mirror used in the ET interferometer under cryogenic temperature. [13][14][15][16] During the cooling down phase, the mirror may be affected by surface topology changes due to mechanical stress and induced vibrations. Kaneda et al showed the topology change of a large mirror working at cryogenic temperatures.…”

Cryogenic Small Dimension Effects and Design-Oriented Scalable Compact Modeling of a 65-nm CMOS Technology

“…Cryogenic CMOS circuits have become increasingly popular in recent years due to their application in quantum computing [1]. Still, they also find use in a much broader spectrum of applications such as gravitational wave detectors [2]- [4], infrared focal plane arrays, positron emission tomography, and quantum technology in general [5]. Modern thin-oxide devices are usually free of the anomalies that plague thickoxide devices [6], [7], [9] and can therefore take full advantage of the benefits offered by the cryogenic environment, such as increased transconductance [9] and reduced leakage [15].…”