arXiv subjects

Christophe Michel

Publications and source records attributed to Christophe Michel.

27 records · Page 2Linked to original sources

arXiv2016

A new method of probing mechanical losses of coatings at cryogenic temperatures

A new method of probing mechanical losses and comparing the corresponding deposition processes of metallic and dielectric coatings in 1-100 MHz frequency range and cryogenic temperatures is presented. The method is based on the use of extremely high-quality quartz acoustic cavities whose internal losses are orders of magnitude lower than any available coatings nowadays. The approach is demonstrated for Chromium, Chromium/Gold and a multilayer tantala/silica coatings. The ${\rm Ta}_2{\rm O}_5/{\rm Si}{\rm O}_2$ coating has been found to exhibit a loss angle lower than $1.6\times10^{-5}$ near 30 {\rm MHz} at 4 {\rm K}. The results are compared to the previous measurements.

physics.ins-det↗

arXiv2016

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.

physics.ins-det↗

arXiv2015

Liquidity costs: a new numerical methodology and an empirical study

We consider rate swaps which pay a fixed rate against a floating rate in presence of bid-ask spread costs. Even for simple models of bid-ask spread costs, there is no explicit strategy optimizing an expected function of the hedging error. We here propose an efficient algorithm based on the stochastic gradient method to compute an approximate optimal strategy without solving a stochastic control problem. We validate our algorithm by numerical experiments. We also develop several variants of the algorithm and discuss their performances in terms of the numerical parameters and the liquidity cost.

q-fin.CP↗

arXiv2015

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.

physics.optics↗

arXiv2014

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 $\pm$ 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 $\pm$ 0.3)x1E-4 at 16 kHz, but this value decreases by one order of magnitude after annealing and the frequency dependence disappears.

physics.ins-det↗

arXiv2013

High quality factor mg-scale silicon mechanical resonators for 3-mode optoacoustic parametric amplifiers

Milligram-scale resonators have been shown to be suitable for the creation of 3-mode optoacoustic parametric amplifiers, based on a phenomena first predicted for advanced gravitational-wave detectors. To achieve practical optoacoustic parametric amplification, high quality factor resonators are required. We present millimetre-scale silicon resonators designed to exhibit a torsional vibration mode with a frequency in the 10^5 - 10^6 Hz range, for observation of 3-mode optoacoustic interactions in a compact table-top system. Our design incorporates an isolation stage and minimizes the acoustic loss from optical coating. We observe a quality factor of 7.5 x 10^5 for a mode frequency of 401.5 kHz, at room temperature and pressure of 10^-3 Pa. We confirmed the mode shape by mapping the amplitude response across the resonator and comparing to finite element modelling. This study contributes towards the development of 3-mode optoacoustic parametric amplifiers for use in novel high-sensitivity signal transducers and quantum measurement experiments.

physics.ins-det↗

arXiv2010

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.

gr-qc↗

arXiv2007

The BMV experiment : a novel apparatus to study the propagation of light in a transverse magnetic field

In this paper, we describe in detail the BMV (Biréfringence Magnétique du Vide) experiment, a novel apparatus to study the propagation of light in a transverse magnetic field. It is based on a very high finesse Fabry-Perot cavity and on pulsed magnets specially designed for this purpose. We justify our technical choices and we present the current status and perspectives.

physics.optics↗

arXiv2006

Titania-doped tantala/silica coatings for gravitational-wave detection

Reducing thermal noise from optical coatings is crucial to reaching the required sensitivity in next generation interferometric gravitational-waves detectors. Here we show that adding TiO$_2$ to Ta$_2$O$_5$ in Ta$_2$O$_5$/SiO$_2$ coatings reduces the internal friction and in addition present data confirming it reduces thermal noise. We also show that TiO$_2$-doped Ta$_2$O$_5$/SiO$_2$ coatings are close to satisfying the optical absorption requirements of second generation gravitational-wave detectors.

gr-qc↗