T1 task- update

Mike Plissi

2

Motivation

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

The mechanical losses associated with the mirror coatings is more relevant than was previously thought

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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Direct thermal noise measurements of thin membranes-INFN VIRGO

During the first year of activity a Fabry-Perot cavity has been realised with a finesse 30000, a bandwidth of 30kHz, and a displacement sensitivity of

The thermal noise of a 20 layer coating has been investigated (see below)

Hzm15103 −×

Frequency

22 / SiOTiO

Paolo Amico

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F.E.M mechanical characterisation

The mechanical behaviour of the test piece has been characterised by a finite element model (see below)

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Sensitivity upgrade of the interferometric system in Perugia

Laser frequency stabilised to a Fabry-Perot reference cavity in order to reduce laser frequency noise

Preliminary frequency stabilisation has been realised with an aluminium cavity

Photo of the optical set-up

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Improved sensitivity curve

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Next steps

Next steps are to replace the temporary cavity with one made from Suprasil 3 and to reduce the electronic noise

Photo of the Suprasil 3 cavity that will replace the aluminium cavity

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Direct thermal noise experiment- IGR Interferometric measurement technique

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

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Frequency stabilisation system

A Pound-Drever-Hall scheme is used

A three path feedback system is used for the frequency stabilisation: Feedback to PZT mounted on laser crystal Feedback to an EOM in the beam path Low frequency temperature feedback

A custom built servo has been constructed and currently performs close to the modelled transfer functions

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Improvements to the laser frequency stabilisation

Performance was limited by losses in the optical set-up resulting in low intrinsic gain from the control system

Work has been done in improving both the optical and RF set-up

The light power into the interferometer has been increased and the mode-matching has been improved

The custom-built servo is now allowing feedback to all three paths and the gain of the EOM path is now much closer to the specification

Reference cavity now locks easily to the TEM-00 mode There is some phase delay at the higher frequencies

limiting the unity gain point to around 60 kHz

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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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Fused silica fibre work

Photo of the new (LabVIEW controlled) fibre pulling machine

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Fibre characterisation

Photo of the apparatus used to measure the vertical bounce frequency

~ 100 m

Optical profile of silica fibre

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Welding fibre to ear

Photo of a fused silica fibre welded (using an electrolytic burner) onto a test ear

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Pendulum suspension installation

Auxiliary optics have been installed Beam alignment of the auxiliary optics has been

completed Cantilever blades used for the vertical isolation of

the monolithic suspensions have been matched for deflection

The pick-off optics for the thermal noise cavity have been pre-adjusted on the optical bench

The electronics for controlling the reaction pendulum are currently being tested

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Installation-mode matching suspension inside the tank

Detail of intermediate mass showingposition of eddy-current dampers

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

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Next steps

Install reaction pendulum Weld fibres to test masses (using purpose built jig)

Installation of short arm cavity

Locking of short arm cavity

Replacement of test mirror with a composite mass to investigate excess noise associated with a large bond area