Abstract
We report on the results of an extensive campaign of optical and mechanical characterization of the ion-beam sputtered oxide layers (Ta
2
O
5
, TiO
2
, Ta
2
O
5
–TiO
2
, SiO
2
) within the ...high-reflection coatings of the Advanced LIGO, Advanced Virgo and KAGRA gravitational-wave detectors: refractive index, thickness, optical absorption, composition, density, internal friction and elastic constants have been measured; the impact of deposition rate and post-deposition annealing on coating internal friction has been assessed. For Ta
2
O
5
and SiO
2
layers, coating internal friction increases with the deposition rate, whereas the annealing treatment either erases or largely reduces the gap between samples with different deposition history. For Ta
2
O
5
–TiO
2
layers, the reduction of internal friction due to TiO
2
doping becomes effective only if coupled with annealing. All measured samples showed a weak dependence of internal friction on frequency
ϕ
c
(
f
) =
af
b
, with −0.208 <
b
< 0.140 depending on the coating material considered. SiO
2
films showed a mode-dependent loss branching, likely due to spurious losses at the coated edge of the samples. The reference loss values of the Advanced LIGO and Advanced Virgo input (ITM) and end (ETM) mirror HR coatings have been updated by using our estimated value of Young’s modulus of Ta
2
O
5
–TiO
2
layers (120 GPa) and are about 10% higher than previous estimations.
Brownian thermal noise associated with highly reflective mirror coatings is a fundamental limit for several precision experiments, including gravitational-wave detectors. Recently, there has been a ...worldwide effort to find mirror coatings with improved thermal noise properties that also fulfill strict optical requirements such as low absorption and scatter. We report on the optical and mechanical properties of ion-beam-sputtered niobia and titania-niobia thin films, and we discuss application of such coatings in current and future gravitational-wave detectors. We also report an updated direct coating thermal noise measurement of the HR coatings used in Advanced LIGO and Advanced Virgo, and the observation of a discrepancy between ring-down measurements and thermal-noise estimations of mechanical loss in highly reflective mirror coatings. This discrepancy might be ascribed either to a dissipation of the silica layers considerably higher than expected or to an unexplained excess loss of stacked layers.
The detection of gravitational waves remains one of the most challenging prospects faced by experimental physicists. One of the most significant limits to the sensitivity of current, and future, ...long-baseline interferometric gravitational wave detectors is thermal displacement noise of the test masses and their suspensions. Suspension thermal noise will be an important noise source at operating frequencies between approximately 10 and 30 Hz, and it results from a combination of thermoelastic damping, surface loss and bulk loss associated with the suspension fibres, and weld loss from their attachment. Its effects can be reduced by minimizing thermoelastic loss and optimizing pendulum dilution factor via the appropriate choice of geometry of the suspension fibre and attachment geometry. This paper will discuss the design and fabrication of a prototype of the fused silica suspension stage for use in the advanced LIGO (aLIGO) detector network, analysing in detail the design of the fused silica attachment pieces (ears), together with the suspension assembly techniques. We also present a full thermal noise analysis of the prototype suspension, taking into account for the first time the precise shape of the actual fibres used, and weld loss. We shall demonstrate the suitability of this suspension for installation into aLIGO.
Neurofibromatosis type 1 (NF1) is an autosomal dominant condition caused by neurofibromin haploinsufficiency due to pathogenic variants in the
NF1
gene. Tumor predisposition has long been associated ...with NF1, and an increased breast cancer (BC) incidence and reduced survival have been reported in recent years for women with NF1. As breast density is another known independent risk factor for BC, this study aims to evaluate the variability of breast density in patients with NF1 compared to the general population. Mammograms from 98 NF1 women affected by NF1, and enrolled onto our monocentric BC screening program, were compared with those from 300 healthy subjects to verify differences in breast density. Mammograms were independently reviewed and scored by a radiologist and using a Computer-Aided Detection (CAD) software. The comparison of breast density between NF1 patients and controls was performed through Chi-squared test and with multivariable ordinal logistic models adjusted for age, body mass index (BMI), number of pregnancies, and menopausal status.breast density was influenced by BMI and menopausal status in both NF1 patients and healthy subjects. No difference in breast density was observed between NF1 patients and the healthy female population, even after considering the potential confounding factors.Although NF1 and a highly fibroglandular breast are known risk factors of BC, in this study, NF1 patients were shown to have comparable breast density to healthy subjects. The presence of pathogenic variants in the
NF1
gene does not influence the breast density value.
The search for gravitational wave signals from astrophysical sources has led to the current work to upgrade the two largest of the long-baseline laser interferometers, the LIGO detectors. The first ...fused silica mirror suspensions for the Advanced LIGO gravitational wave detectors have been installed at the LIGO Hanford and Livingston sites. These quadruple pendulums use synthetic fused silica fibers produced using a CO2 laser pulling machine to reduce thermal noise in the final suspension stage. The suspension thermal noise in Advanced LIGO is predicted to be limited by internal damping in the surface layer of the fibers, damping in the weld regions, and the strength of the fibers. We present here a new method for increasing the fracture strength of fused silica fibers by laser polishing of the stock material from which they are produced. We also show measurements of mechanical loss in laser polished fibers, showing a reduction of 30% in internal damping in the surface layer.
Undoped sapphire rod crystals (
= 3 mm, length 170 mm) along different crystallographic orientations (
a
112&cmb.macr;0,
m
101&cmb.macr;0,
c
0001 and
c
0001 shifted 30° off axis) were successfully ...grown by the micro-pulling down (μ-PD) method. The bubble defect distribution was investigated as a function of the thermal gradient and pulling rates. It is observed that sapphire rods grown at a low pulling rate (
v
< 200 μm min
−1
) were bubble-free. A homogeneous temperature distribution around the capillary die will limit the bubble propagation. Pulling sapphire rods along the
c
-axis is a good way to minimize the bubble propagation. The effects of growth parameters on bubble and strain distribution in sapphire rods grown from μ-PD rods were discussed.
Undoped sapphire rod crystals along different crystallographic orientations (
a
112&cmb.macr;0,
m
101&cmb.macr;0,
c
0001 and
c
0001 shifted 30° off axis) were successfully grown by the micro-pulling down (μ-PD) method.
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