T1 task- update

Mike Plissi

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Collaboration

Groups actively involved INFN-VIRGO MAT IGR-Glasgow

Groups that have expressed interest INFN-AURIGA CNRS-LKB INFN-LENS

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Motivation Future detectors will use crystalline materials for the

test masses Thermo-elastic noise is higher than the ‘intrinsic’

noise in crystalline materials There are several sources of thermo-elastic noise

including the dielectric mirror coatings and the silicate bonds used to attach the suspension fibres to the test masses

Direct measurement of the thermal noise is necessary in order to compare with calculations

Study of time-series data will enable searches for excess impulsive events due to stress (e.g. in bonds)

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Sensitivity upgrade of the interferometric system in Perugia

The sensitivity upgrade is under development The system uses a reference cavity stabilization

scheme A non-monolithic prototype has been realised as a

first step The final reference cavity will be made from fused

silica

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Direct thermal noise measurements of thin membranes-INFN VIRGO

The thermal noise of thin membranes will be measured initially on fused silica substrates and then on silicon substrates

The measurement facility consists of a high-finesse Fabry-Perot cavity

The cavity (plano-concave geometry) is constructed with a commercial high reflectivity mirror and a fused silica membrane (50 microns thick) with a high reflectivity mirror coated on the polished surface

The reflection signal is extracted using a Pound-Drever-Hall technique

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Direct thermal noise experiment-IGR Glasgow

Our proposal is to use a new test system, built within our JIF-funded laboratory, to allow direct measurement of thermal noise in fused silica and silicon suspensions and to search for excess noise in composite structures built using hydroxy-catalysis bonding

The JIF interferometer is in the process of being commissioned

We have constructed our 10 m reference cavity and are stabilising the frequency of the laser to this cavity

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Direct thermal noise experiment Interferometric measurement technique

Goal: reduce other noise to well below thermal noiseTarget sensitivity is at 1kHz Hzm/103 20

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Laser frequency stabilisation A Pound-Drever-Hall scheme is used A three path feedback system will be used for the

frequency stabilisation:1. Feedback to PZT mounted on laser crystal2. Feedback to an EOM in the beam path3. Low frequency temperature feedback

A custom built servo has been constructed and currently performs close to the modelled transfer functions but still needs to be commissioned in situ

Currently possible to lock reference cavity for extended periods (several minutes) using standard pre-amps to process the feedback signal

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Reference cavity locking

Images taken from CCD camera positioned behind end mirror of the reference cavity showing locked state (right hand image)

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Short cavity suspension rig Double pendulum

suspensions with enhanced vertical isolation

Monolithic suspension for each cavity mirror

short arm cavity

suspended reaction mass(used to apply feedback forces)

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Installation-mode matching suspension inside the tank

Detail of intermediate mass showingposition of eddy-current damping coils(photo was taken before the coils were wound)

Photo showing part of the supporting frame and the double pendulum suspension for the mode matching optic

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Next steps Implement custom servo to feed back to all three

paths Will allow extended locking times

Installation of short arm cavity

Locking of short arm cavity