Amorphous optical coatings of present gravitational-wave interferometers*

Granata, M.; Amato, A.; Balzarini, Laurent; Canepa, M.; Degallaix, J.; Forest, Danièle; Dolique, V.; Mereni, L.; Michel, C.; Pinard, L.; Sassolas, B.; Teillon, Julien; Cagnoli, G.

doi:10.1088/1361-6382/ab77e9

Cited by 82 publications

(184 citation statements)

References 67 publications

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“…More specifically, amorphous tantala is an ideal candidate as a benchmark system, given the wide set of experimental, e.g., Refs. [47][48][49][50][51][52][53][54][55][56], and numerical [36,57] studies.…”

Section: Introductionmentioning

confidence: 99%

In silicobroadband mechanical spectroscopy of amorphous tantala

Puosi

Fidecaro

Capaccioli

et al. 2019

Phys. Rev. Research

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Adopting an agnostic approach, the quality factor Q of tantala glass is drawn via in silico mechanical spectroscopy in wide ranges of temperature (10-300 K) and frequency (500 MHz f 1 THz). At the highest frequencies, Q ∝ f −3 , consistent with Rayleigh sound scattering. For frequencies lower than terahertz, losses exhibit a weak power-law frequency dependence Q ∝ f −α with α ∼ 0.1 to 0.2, depending on glass preparation and temperature. Arguing the validity of the power law down to 1 kHz, we show striking agreement with the losses measured in annealed amorphous films in the whole temperature range, revealing similitude between disordered structures created by different routes (quench cooling and deposition). Our results do not support the scenario of the mechanical loss due to activated relaxation of independent two-level systems.

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Section: Introductionmentioning

confidence: 99%

In silicobroadband mechanical spectroscopy of amorphous tantala

Puosi

Fidecaro

Capaccioli

et al. 2019

Phys. Rev. Research

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“…In this analysis we assumed that thickness and density are constant, since we do not have yet a measurement of how those film properties change with annealing. This assumption is likely wrong, since changes of density, thickness and refractive index have been observed for other amorphous materials [6,25,26]. However, we note that the estimate of Y and ν depends mostly on the product of thickness and density, that is, the surface density of the material.…”

Section: Measurementsmentioning

confidence: 83%

“…The relative difference between the coated and uncoated disk frequencies is roughly constant between 1 and 30 KHz, and equal to about 300 ppm, with variation between modes of the order of 10-30 ppm, related to the film Poisson ratio. We used a finite element analysis (FEA) carried out in COMSOL to find the values of the film material Young's modulus Y and Poisson ratio ν that best reproduce the measured changes in resonant frequencies [6]. Instead of using directly COMSOL in the fit procedure, we first produced a random sampling of the film properties space [Y, ν, t, ρ] and run a FEA for each point.…”

Section: Measurementsmentioning

confidence: 99%

“…We use the model described in Hong et al [13] (in particular starting from equation 94 therein), where the properties of the component materials and the geometry of the layers are used to predict the total thermal noise. Possible effects due to the transition between layers are not considered [6,29]. We consider a high reflection coating composed of 38 alternating layers of silica (low index material) and titania- doped tantala (high index material), each with an optical thickness of λ/4 where the laser wave-length λ in vacuum is 1064 nm, to obtain a nominal transmission of about 5 ppm [30].…”

Section: Effect On Thermal Noise Estimatementioning

confidence: 99%

“…The ultimate limit to the length stability of such cavities is often determined by thermal motion of the cavity components. In many cases, such as in interferometric gravitational wave (GW) detectors [1][2][3][4], the limit thermal noise comes from the Brownian motion of the dielectric coatings deposited on the mirrors [5], and composed of alternating layers of amorphous oxides: silica and titania-doped tantala for the Advanced GW detectors [6]. The amplitude of Brownian noise can be linked to the material internal friction by use of the Fluctuation-Dissipation Theorem [7,8].…”

Section: Introductionmentioning

confidence: 99%

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Method for the experimental measurement of bulk and shear loss angles in amorphous thin films

et al. 2020

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Brownian thermal noise is a limiting factor for the sensitivity of many high precision metrology applications, among other gravitational-wave detectors. The origin of Brownian noise can be traced down to internal friction in the amorphous materials that are used for the high reflection coatings. To properly characterize the internal friction in an amorphous material, one needs to consider separately the bulk and shear losses. In most of previous works the two loss angles were considered equal, although without any first principle motivation. In this work we present a method that can be used to extract the material bulk and shear loss angles, based on current state-of-the-art coating ring-down measurement systems. We also show that for titania-doped tantala, a material commonly used in gravitational-wave detector coatings, the experimental data strongly favor a model with two different and distinct loss angles, over the simpler case of one single loss angle. arXiv:1911.12277v2 [cond-mat.mtrl-sci]

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Mirror Surface Nanostructuring via Laser Direct Writing—Characterization and Physical Origins

Vretenar

Puplauskis

Klaers

2023

Advanced Optical Materials

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advances to this method, perform timeresolved measurements of the process, and analyze its physical origins.Thanks to this novel nanostructuring method, open-access optical microcavities have become a very flexible platform for experiments with two-dimensional photon gases, in particular, for the study of lasing phenomena and photon Bose-Einstein condensation (BEC). [8][9][10][11][12][13] A major future application of such systems may be spin glass simulation, allowing the system to be used as a computing platform. [14] Furthermore, the study of polaritonic quantum gases based on open cavities [15,16] may benefit from this method. Beyond studying optical condensation phenomena, nanostructuring of high-reflectivity mirrors via laser direct writing may also find novel applications in areas such as cavity ringdown spectroscopy, [17] wavefront shaping, [18] and precision interferometry [19,20] (and references therein).In addition to the permanent modification of mirror surfaces, it is also desirable to perform time-dependent control over the transverse flow of light in microcavities. Mirrors with integrated piezo arrays, [21] heater arrays, [22] and electrostatic membranes [23] may be used for this purpose. As in the previously discussed case of permanent nanostructuring, [7] absorptive layers in the mirror also offer a solution to the problem of time-dependent control. This includes refractive-index tuning via laser writing of the thermo-responsive polymer poly(N-isopropylacrylamide) (pNIPAM) [24] added to the cavity medium, and thermal expansion of the mirror surface, which will be demonstrated in this paper. The former introduces an attractive potential, while the latter creates a repulsive potential. Since both techniques work on different timescales, they may be used in a complementary manner. Additionally, a certain degree of spatial complexity can be introduced by wavefront shaping the heating laser.The dielectric mirrors used in this work are produced using ion beam sputtering (IBS), and have the following composition: a fused silica substrate, atop which lies an optically absorptive amorphous silicon layer of 30 nm thickness, followed by a quarter-wave dielectric stack with a reflectivity maximum at a wavelength of 600 nm. In most measurements presented in this work, this dielectric stack consists of 20 pairs of Ta 2 O 5 and SiO 2 . However, we also evaluate thinner dielectric stacks with 11 and 10 pairs. The essential point of this mirror design is the absorptive Si layer that provides a way to locally heat the dielectric stack and the optical medium using laser light-which is the basis of all the phenomena we show in this paper. In the first part of this work, we will demonstrate that such mirrorsThe addition of an optically absorptive layer to otherwise standard dielectric mirrors enables a set of laser direct writing nanostructuring methods that can add functionality to such mirrors while retaining their high reflectivity. A thorough characterization of this method is given in this paper, and its physic...

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Amorphous optical coatings of present gravitational-wave interferometers*

Cited by 82 publications

References 67 publications

In silicobroadband mechanical spectroscopy of amorphous tantala

In silicobroadband mechanical spectroscopy of amorphous tantala

Method for the experimental measurement of bulk and shear loss angles in amorphous thin films

Mirror Surface Nanostructuring via Laser Direct Writing—Characterization and Physical Origins

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