arXiv subjects

P. F. Cohadon

Publications and source records attributed to P. F. Cohadon.

8 recordsLinked to original sources

arXiv2018

Calibration of Advanced Virgo and Reconstruction of the Gravitational Wave Signal h(t) during the Observing Run O2

In August 2017, Advanced Virgo joined Advanced LIGO for the end of the O2 run, leading to the first gravitational waves detections with the three-detector network. This paper describes the Advanced Virgo calibration and the gravitational wave strain h(t) reconstruction during O2. The methods are the same as the ones developed for the initial Virgo detector and have already been described in previous publications, this paper summarizes the differences and emphasis is put on estimating systematic uncertainties. Three versions of the h(t) signal have been computed for the Virgo O2 run, an online version and two post-run reprocessed versions with improved detector calibration and reconstruction algorithm. A photon calibrator has been used to establish the sign of h(t) and to make an independent partial cross-check of the systematic uncertainties. The uncertainties reached for the latest h(t) version are 5.1% in amplitude, 40 mrad in phase and 20 microseconds in timing.

gr-qc↗

arXiv2014

2D photonic-crystal optomechanical nanoresonator

We present the optical optimization of an optomechanical device based on a suspended InP membrane patterned with a 2D near-wavelength grating (NWG) based on a 2D photonic-crystal geometry. We first identify by numerical simulation a set of geometrical parameters providing a reflectivity higher than 99.8 % over a 50-nm span. We then study the limitations induced by the finite value of the optical waist and lateral size of the NWG pattern using different numerical approaches. The NWG grating, pierced in a suspended InP 265 nm-thick membrane, is used to form a compact microcavity involving the suspended nano-membrane as end mirror. The resulting cavity has a waist size smaller than 10 $μ$m and a finesse in the 200 range. It is used to probe the Brownian motion of the mechanical modes of the nanomembrane.

cond-mat.mes-hall↗

arXiv2003

Optomechanical characterization of acoustic modes in a mirror

We present an experimental study of the internal mechanical vibration modes of a mirror. We determine the frequency repartition of acoustic resonances via a spectral analysis of the Brownian motion of the mirror, and the spatial profile of the acoustic modes by monitoring their mechanical response to a resonant radiation pressure force swept across the mirror surface. We have applied this technique to mirrors with cylindrical and plano-convex geometries, and compared the experimental results to theoretical predictions. We have in particular observed the gaussian modes predicted for plano-convex mirrors.

quant-ph↗

arXiv2003

Optical phase-space reconstruction of mirror position at the attometer level

We describe an experiment in which the quadratures of the position of an harmonically-bound mirror are observed at the attometer level. We have studied the Brownian motion of the mirror, both in the free regime and in the cold-damped regime when an external viscous force is applied by radiation pressure. We have also studied the thermal-noise squeezing when the external force is parametrically modulated. We have observed both the 50% theoretical limit of squeezing at low gain and the parametric oscillation of the mirror for a large gain.

quant-ph↗

arXiv2000

Full mechanical characterization of a cold damped mirror

We describe an experiment in which we have used a cold damping feedback mechanism to reduce the thermal noise of a mirror around its mechanical resonance frequency. The monitoring of the brownian motion of the mirror allows to apply an additional viscous force without any thermal fluctuations associated. This scheme has been experimentally implemented with the radiation pressure of an intensity-modulated laser beam. Large noise reductions, up to 30 dB, have been obtained. We have also checked the mechanical response of the cold damped mirror, and monitored its transient evolution between the cooled regime and the room temperature equilibrium. A simple theoretical model allows to fully explain the experimental results. A possible application to the active cooling of the violin modes in a gravitational-wave interferometer is discussed.

quant-ph↗

arXiv2000

Thermal noise of a plano-convex mirror

We study theoretically the internal thermal noise of a mirror coated on a plano-convex substrate. The comparison with a cylindrical mirror of the same mass shows that the effect on a light beam can be reduced by a factor 10, improving the sensitivity of high-precision optical experiments such as gravitational-wave interferometers.

quant-ph↗

arXiv1999

Cooling of a mirror by radiation pressure

We describe an experiment in which a mirror is cooled by the radiation pressure of light. A high-finesse optical cavity with a mirror coated on a mechanical resonator is used as an optomechanical sensor of the Brownian motion of the mirror. A feedback mechanism controls this motion via the radiation pressure of a laser beam reflected on the mirror. We have observed either a cooling or a heating of the mirror, depending on the gain of the feedback loop.

quant-ph↗

arXiv1999

High-sensitivity optical measurement of mechanical Brownian motion

We describe an experiment in which a laser beam is sent into a high-finesse optical cavity with a mirror coated on a mechanical resonator. We show that the reflected light is very sensitive to small mirror displacements. We have observed the Brownian motion of the resonator with a very high sensitivity.

quant-ph↗