15 research outputs found
Material loss angles from direct measurements of broadband thermal noise
International audienceWe estimate the loss angles of the materials currently used in the highly reflective test-mass coatings of interferometric detectors of gravitational waves, namely Silica, Tantala, and Ti-doped Tantala, from direct measurement of coating thermal noise in an optical interferometer testbench, the Caltech TNI. We also present a simple predictive theory for the material properties of amorphous glassy oxide mixtures, which gives results in good agreement with our measurements on Ti-doped Tantala. Alternative measurement methods and results are reviewed, and some critical issues are discussed
A Xylophone Configuration for a third Generation Gravitational Wave Detector
Achieving the demanding sensitivity and bandwidth, envisaged for third
generation gravitational wave (GW) observatories, is extremely challenging with
a single broadband interferometer. Very high optical powers (Megawatts) are
required to reduce the quantum noise contribution at high frequencies, while
the interferometer mirrors have to be cooled to cryogenic temperatures in order
to reduce thermal noise sources at low frequencies. To resolve this potential
conflict of cryogenic test masses with high thermal load, we present a
conceptual design for a 2-band xylophone configuration for a third generation
GW observatory, composed of a high-power, high-frequency interferometer and a
cryogenic low-power, low-frequency instrument. Featuring inspiral ranges of
3200Mpc and 38000Mpc for binary neutron stars and binary black holes
coalesences, respectively, we find that the potential sensitivity of xylophone
configurations can be significantly wider and better than what is possible in a
single broadband interferometer
Mechanical loss in state-of-the-art amorphous optical coatings
We present the results of mechanical characterizations of many different
high-quality optical coatings made of ion-beam-sputtered titania-doped tantala
and silica, developed originally for interferometric gravitational-wave
detectors. Our data show that in multi-layer stacks (like high-reflection Bragg
mirrors, for example) the measured coating dissipation is systematically higher
than the expectation and is correlated with the stress condition in the sample.
This has a particular relevance for the noise budget of current advanced
gravitational-wave interferometers, and, more generally, for any experiment
involving thermal-noise limited optical cavities.Comment: 31 pages, 14 figure
Measurement of Thermal Noise in Multilayer Coatings with Optimized Layer Thickness
A standard quarter-wavelength multilayer optical coating will produce the
highest reflectivity for a given number of coating layers, but in general it
will not yield the lowest thermal noise for a prescribed reflectivity. Coatings
with the layer thicknesses optimized to minimize thermal noise could be useful
in future generation interferometric gravitational wave detectors where coating
thermal noise is expected to limit the sensitivity of the instrument. We
present the results of direct measurements of the thermal noise of a standard
quarter-wavelength coating and a low noise optimized coating. The measurements
indicate a reduction in thermal noise in line with modeling predictions.Comment: 8 pages, 14 figure
Measurements of mechanical thermal noise and energy dissipation in optical dielectric coatings
In recent years an increasing number of devices and experiments are shown to
be limited by mechanical thermal noise. In particular sub-Hertz laser frequency
stabilization and gravitational wave detectors, that are able to measure
fluctuations of 1E-18 m/rtHz or less, are being limited by thermal noise in the
dielectric coatings deposited on mirrors. In this paper we present a new
measurement of thermal noise in low absorption dielectric coatings deposited on
micro-cantilevers and we compare it with the results obtained from the
mechanical loss measurements. The coating thermal noise is measured on the
widest range of frequencies with the highest signal to noise ratio ever
achieved. In addition we present a novel technique to deduce the coating
mechanical losses from the measurement of the mechanical quality factor which
does not rely on the knowledge of the coating and substrate Young moduli. The
dielectric coatings are deposited by ion beam sputtering. The results presented
here give a frequency independent loss angle of (4.70 0.2)x1E-4 with a
Young's modulus of 118 GPa for annealed tantala from 10 Hz to 20 kHz. For
as-deposited silica, a weak frequency dependence (~ f^{-0.025}) is observed in
this frequency range, with a Young's modulus of 70 GPa and an internal damping
of (6.0 0.3)x1E-4 at 16 kHz, but this value decreases by one order of
magnitude after annealing and the frequency dependence disappears.Comment: Accepted for publication in Phys. Rev.
Material loss angles from direct measurements of broadband thermal noise
We estimate the loss angles of the materials currently used in the highly
reflective test-mass coatings of interferometric detectors of gravitational
waves, namely Silica, Tantala, and Ti-dop ed Tantala, from direct measurement
of coating thermal noise in an optical interferometer testbench, the Caltech
TNI. We also present a simple predictive theory for the material properties of
amorphous glassy oxide mixtures, which gives results in good agreement with our
measurements on Ti-doped Tantala. Alternative measure ment methods and results
are reviewed, and some critical issues are discussed
Low loss coatings for the VIRGO large mirrors
présentée par L. PinardThe goal of the VIRGO program is to build a giant Michelson type interferometer (3 kilometer long arms) to detect gravitational waves. Large optical components (350 mm in diameter), having extremely low loss at 1064 nm, are needed. Today, the Ion beam Sputtering is the only deposition technique able to produce optical components with such performances. Consequently, a large ion beam sputtering deposition system was built to coat large optics up to 700 mm in diameter. The performances of this coater are described in term of layer uniformity on large scale and optical losses (absorption and scattering characterization). The VIRGO interferometer needs six main mirrors. The first set was ready in June 2002 and its installation is in progress on the VIRGO site (Italy). The optical performances of this first set are discussed. The requirements at 1064 nm are all satisfied. Indeed, the absorption level is close to 1 ppm (part per million), the scattering is lower than 5 ppm and the R.M.S. wavefront of these optics is lower than 8 nm on 150 mm in diameter. Finally, some solutions are proposed to further improve these performances, especially the absorption level (lower than 0.1 ppm) and the mechanical quality factor Q of the mirrors (thermal noise reduction)