1. T1 task- update Mike Plissi

2. 2 Collaboration Groups actively involved INFN-VIRGO MAT IGR-Glasgow Groups that have expressed interest INFN-AURIGA CNRS-LKB INFN-LENS

3. 3 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)

4. 4 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

5. 5 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

6. 6 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

7. 7 Direct thermal noise experiment  Interferometric measurement technique  Goal: reduce other noise to well below thermal noise  Target sensitivity is at 1kHz

8. 8 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 crystal 2.Feedback to an EOM in the beam path 3.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

9. 9 Reference cavity locking Images taken from CCD camera positioned behind end mirror of the reference cavity showing locked state (right hand image)

10. 10 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)

11. 11 Installation-mode matching suspension inside the tank Detail of intermediate mass showing position 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

12. 12 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