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.
Several sources of noise limit the sensitivity of current gravitational wave detectors. Currently, dominant noise sources include quantum noise and thermal Brownian noise, but future detectors will ...also be limited by other thermal noise channels. In this paper, we study a thermal noise source which is caused by spatial charge carrier density variations in semiconductor materials. We provide an analytical model for the understanding of charge carrier fluctuations under the presence of screening effects and show that charge carrier noise will not be a limiting noise source for third-generation gravitational wave detectors.
We present a formalism to compute Brownian thermal noise in functional optical surfaces such as grating reflectors, photonic crystal slabs, or complex metamaterials. Such computations are based on a ...specific readout variable, typically a surface integral of a dielectric interface displacement weighed by a form factor. This paper shows how to relate this form factor to Maxwell’s stress tensor computed on all interfaces of the moving surface. As an example, we examine Brownian thermal noise in monolithic T-shaped grating reflectors. The previous computations by Heinert et al. Phys. Rev. D 88, 042001 (2013) utilizing a simplified readout form factor produced estimates of thermal noise that are tens of percent higher than those of the exact analysis in the present paper. The relation between the form factor and Maxwell’s stress tensor implies a close correlation between the optical properties of functional optical surfaces and thermal noise.
We report in this article on the measurement of the optical absorption of moderately doped crystalline silicon samples at 1550 nm, which is a candidate material for the main optics of the low ...temperature interferometer of the Einstein Telescope (ET). We observe a nearly constant absorption from room temperature down to cryogenic temperatures for two silicon samples presenting an optical absorption of 0.029 cm−1 and 780 ppm cm−1, both crystals doped with boron. This is in contradiction to what was assumed previously-a negligible optical absorption at low temperature due to the carrier freezeout. As the main consequence, if the silicon intrinsic absorption can not be lowered, the cross section of the mirror suspension of the ET must be increased to be able to carry away the excess heat generated by the partially absorbed laser beam during the operation of the interferometer.
Thermal noise associated with the dielectric optical coatings used to form the mirrors of interferometric gravitational wave detectors is expected to be an important limit to the sensitivity of ...future detectors. Improvements in detector performance are likely to require coating materials of lower mechanical dissipation. Typically, current coatings use multiple alternating layers of ion-beam-sputtered amorphous silica and tantalum pentoxide (doped with titania). We present here measurements of the mechanical dissipation of promising alternative crystalline coatings that use multi-layers of single crystal gallium phosphide (GaP) and aluminium gallium phosphide (AlGaP) that are epitaxially grown and lattice matched to a silicon substrate. Analysis shows that the dissipation of the crystalline coating materials appears to be significantly lower than that of the currently used amorphous coatings, potentially enabling a reduction of coating thermal noise in future gravitational wave detectors.
Thermal noise of folding mirrors Heinert, D.; Craig, K.; Grote, H. ...
Physical review. D, Particles, fields, gravitation, and cosmology,
08/2014, Letnik:
90, Številka:
4
Journal Article
Recenzirano
Odprti dostop
Current gravitational-wave detectors rely on the use of Michelson interferometers. One crucial limitation of their sensitivity is the thermal noise of their optical components. Thus, for example, ...fluctuational deformations of the mirror surface are probed by a laser beam being reflected from the mirrors at normal incidence. Thermal noise models are well evolved for that case but mainly restricted to single reflections. In this work, we present the effect of two consecutive reflections under a non-normal incidence onto mirror thermal noise. This situation is inherent to detectors using a geometrical folding scheme such as GEO 600. We revise in detail the conventional direct noise analysis scheme to the situation of non-normal incidence allowing for a modified weighting function of mirror fluctuations. An application of these results to the GEO 600 folding mirror for Brownian, thermoelastic, and thermorefractive noise yields an increase of displacement noise amplitude by 20% for most noise processes. The amplitude of thermoelastic substrate noise is increased by a factor of 4 due to the modified weighting function. Thus, the consideration of the correct weighting scheme can drastically alter the noise predictions and demands special care in any thermal noise design process.
Studies of the mechanical loss of silicon flexures in a temperature region from 5 to 300 K are presented, where the flexures have been prepared by different fabrication techniques of interest for the ...construction of suspension elements of future interferometric gravitational wave detectors. A lowest mechanical loss of 3 × 10−8 was observed for a 130 μm thick flexure at around 10 K. While the mechanical loss follows the thermo-elastic predictions down to 50 K, at lower temperatures the observed loss is found to be a function of surface roughness. This surface loss is of interest for all applications using silicon-based oscillators at low temperatures. The extraction of a surface loss parameter using results from our measurements and those of other authors is presented and the relevance for future gravitational wave detector suspensions is discussed. A surface loss parameter αs = 0.5 pm was obtained. This reveals that the surface loss of silicon is significantly lower than the surface loss of fused silica.
The arm cavities of real gravitational wave detectors can show small deviations like a tilt or a spatial shift between the cavity mirrors. These deviations lead to a separation of the optical mode ...centres with respect to the mirrorʼs centre. In this Letter we perform the computation of parametric instable modes considering the described displacement. We further analyse the possibility of parametric oscillatory instability in the Advanced LIGO interferometer for the case of a displaced arm cavity. Our results reveal an additional number of optical and elastic mode combinations due to a displacement that can give rise to the undesirable effect of parametric oscillatory instability.
► We analyse the possibility of parametric oscillatory instability in the Advanced LIGO interferometer. ► We perform the computation of parametric instable modes considering the mirror displacement. ► Our results reveal an additional number of optical and elastic mode unstable combinations.
Future gravitational wave detectors will be limited by different kinds of noise. Thermal noise from the coatings and the substrate material will be a serious noise contribution within the detection ...band of these detectors. Cooling and the use of a high mechanical Q-factor material as a substrate material will reduce the thermal noise contribution from the substrates. Silicon is one of the most interesting materials for a third generation cryogenic detector. Due to the fact that the coefficient of thermal expansion vanishes at 18 and 125 K the thermoelastic contribution to the thermal noise will disappear. We present a systematic analysis of the mechanical Q-factor at low temperatures between 5 and 300 K on bulk silicon (100) samples which are boron doped. The thickness of the cylindrical samples is varied between 6, 12, 24, and 75mm with a constant diameter of 3 inches. For the 75mm substrate a comparison between the (100) and the (111) orientation is presented. In order to obtain the mechanical Q-factor a ring-down measurement is performed. Thus, the substrate is excited to resonant vibrations by means of an electrostatic driving plate and the subsequent ring-down is recorded using a Michelson-like interferometer. The substrate itself is suspended as a pendulum by means of a tungsten wire loop. All measurements are carried out in a special cryostat which provides a temperature stability of better than 0.1K between 5 and 300K during the experiment. The influence of the suspension on the measurements is experimentally investigated and discussed. At 5.8K a highest Q-factor of 4.5 × 108 was achieved for the 14.9 kHz mode of a silicon (100) substrate with a diameter of 3 inches and a thickness of 12 mm.
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