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)

3 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) Frequency Paolo Amico

4 F.E.M mechanical characterisation The mechanical behaviour of the test piece has been characterised by a finite element model (see below)

5 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

6 Improved sensitivity curve Displacement sensitivity

7 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

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

9 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

10 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

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

12 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)

13 Fused silica fibre work Photo of the new (LabVIEW controlled) fibre pulling machine

14 Fibre characterisation Photo of the apparatus used to measure the vertical bounce frequency ~ 100  m Optical profile of silica fibre

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

16 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

17 Installation-mode matching suspension inside the tank Detail of intermediate mass showing position of eddy-current dampers Photo showing part of the supporting frame and the double pendulum suspension for the mode matching optic

18 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