Optical properties of high-quality oxide coating materials used in gravitational-wave advanced detectors

Amato, A.; Terreni, S.; Dolique, V.; Forest, Danièle; Gemme, G.; Granata, M.; Mereni, L.; Michel, C.; Pinard, L.; Sassolas, B.; Teillon, Julien; Cagnoli, G.; Canepa, M.

doi:10.1088/2515-7639/ab206e

Cited by 40 publications

(52 citation statements)

References 33 publications

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“…The substrate data have been analysed by the WVASE GenOsc routine considering an ultra-thin oxide (about 2 nm resulting from fit); some details on this analysis was included in ref. 8 . • We have fitted the substrate + coating data in the transparency range of the coating with interpolation formula (Cauchy, Sellmeier) to obtain a first reliable estimate of NIR refractive index and coating thickness (as done in ref.…”

Section: Resultsmentioning

confidence: 99%

“…Notably, in gravitational-wave astronomy, AO multilayers represent the key elements of high performance Bragg reflectors which are exploited in the Fabry-Perot cavities of wide-area, giant interferometer detectors (GWD) [4][5][6] . Indeed, multilayers made of Ti:Ta 2 O 5 (the high-index material) and silica (SiO 2 , the low-index material) deposited on massive, large-area fused silica substrates have been adopted by Advanced LIGO (aLIGO) and Advanced Virgo (AdV) detectors 7,8 , contributing to the recent, first observations of gravitational waves 9 . For these GWD applications, in addition to the highest optical quality, very low internal friction is the necessary requirement to have low thermal noise 10 .…”

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confidence: 99%

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Observation of a Correlation Between Internal friction and Urbach Energy in Amorphous Oxides Thin Films

Amato

Terreni

Granata

et al. 2020

Sci Rep

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We have investigated by spectroscopic ellipsometry (SE, 190-1700 nm) the optical properties of uniform, amorphous thin films of Ta 2 o 5 and nb 2 o 5 as deposited and after annealing, and after so-called "doping" with ti atoms which leads to mixed oxides. ta 2 o 5 and ti:ta 2 o 5 are currently used as high-index components in Bragg reflectors for Gravitational Wave Detectors. Parallel to the optical investigation, we measured the mechanical energy dissipation of the same coatings, through the so-called "loss angle" φ = Q −1 , which quantifies the energy loss in materials. By applying the well-known Cody-Lorentz model in the analysis of Se data we have been able to derive accurate information on the fundamental absorption edge through important parameters related to the electronic density of states, such as the optical gap (E g) and the energy width of the exponential Urbach tail (the Urbach energy E U). We have found that E U is neatly reduced by suitable annealing as is also perceptible from direct inspection of Se data. ti-doping also points to a minor decrease of E U. the reduction of E U parallels a lowering of the mechanical losses quantified by the loss angle φ. the correlation highlights that both the electronic states responsible of Urbach tail and the internal friction are sensitive to a self-correlation of defects on a medium-range scale, which is promoted by annealing and in our case, to a lesser extent, by doping. these observations may contribute to a better understanding of the relationship between structural and mechanical properties in amorphous oxides.

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Section: Resultsmentioning

confidence: 99%

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confidence: 99%

Observation of a Correlation Between Internal friction and Urbach Energy in Amorphous Oxides Thin Films

Amato

Terreni

Granata

et al. 2020

Sci Rep

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“…As a matter of facts, careful characterizations of the refractive index and extinction coefficient at the interferometer operational wavelength are necessary 6,7 as well as a determination of the actual thickness of layers. Spectroscopic Ellipsometry (SE) measurements can provide accurate information in this respect as demonstrated by several works 8,9 . This paper however wants to focus on another relevant aspect.…”

Section: Introductionmentioning

confidence: 99%

Effect of heating treatment and mixture on optical properties of coating materials used in gravitational-wave detectors

Amato

Terreni

Michel

et al. 2019

Journal of Vacuum Science &Amp; Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phen

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The interferometer mirrors of Gravitational-Wave Detectors (GWD) are Bragg reflectors made of alternate amorphous silica (SiO 2 ) and titania-doped tantala (TiO 2 :Ta 2 O 5 ) layers as low-and high-refractive index material, respectively. A thermal treatment is usually performed to reduce both mechanical losses and NIR optical absorptions of the coatings. We present a spectroscopic ellipsometry (SE) investigation of the effect of annealing and Ti:Ta mixing on Ta 2 O 5 coatings deposited under conditions similar to those adopted for building up mirrors of GWDs. The broad-band analysis covers both the NIR and the fundamental absorption threshold region. The data show an evident annealing-induced reduction of the fundamental optical absorption broadening. Modelling the data through the Cody-Lorentz formula confirms that NIR absorption are below the SE sensitivity and shows a notable annealing-induced reduction of so-called Urbach tails. Titania-doping of tantala slightly reduces the Urbach energy. After the heating treatment the resulting Urbach energy of the doped material is lower than the one of annealed pure tantala. The observed reduction of Urbach tails is important because it parallels the reduction of so-called internal friction observed in mechanical measurements. So that SE emerges as a convenient tool for an agile diagnostic of both optical and mechanical quality of amorphous oxide coatings.

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“…Current mirrors in GW detectors use a stack of silica material (SiO 2 ) and titanium-doped tantalum (Ti:Ta 2 O 5 ) deposited on a large silica substrate [ 22 ]. The optical characterization of these materials by spectroscopic ellipsometry is reported in Reference [ 23 ]. Recently, high-reflection dielectric Bragg mirrors were manufactured for the Virgo installation, consisting of two materials: a layer of silica with a low refractive index ( n = 1.45 at 1064 nm) and titania-doped tantala with a high refractive index ( n = 2.09) [ 24 ].…”

Section: Discussionmentioning

confidence: 99%

Small-Sized Interferometer with Fabry–Perot Resonators for Gravitational Wave Detection

Petrov

Пустовойт

2021

Sensors

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It is highly desirable to have a compact laser interferometer for detecting gravitational waves. Here, a small-sized tabletop laser interferometer with Fabry–Perot resonators consisting of two spatially distributed “mirrors” for detecting gravitational waves is proposed. It is shown that the spectral resolution of 10−23 cm−1 can be achieved at a distance between mirrors of only 1–3 m. The influence of light absorption in crystals on the limiting resolution of such resonators is also studied. A higher sensitivity of the interferometer to shorter-wave laser radiation is shown. A method for detecting gravitational waves is proposed based on the measurement of the correlation function of the radiation intensities of non-zero-order resonant modes from the two arms of the Mach–Zehnder interferometer.

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Optical properties of high-quality oxide coating materials used in gravitational-wave advanced detectors

Cited by 40 publications

References 33 publications

Observation of a Correlation Between Internal friction and Urbach Energy in Amorphous Oxides Thin Films

Observation of a Correlation Between Internal friction and Urbach Energy in Amorphous Oxides Thin Films

Effect of heating treatment and mixture on optical properties of coating materials used in gravitational-wave detectors

Small-Sized Interferometer with Fabry–Perot Resonators for Gravitational Wave Detection

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