1. STREGA WP4 coating development GEO LIGO ISA Scientific motivation: Mechanical dissipation from dielectric mirror coatings is predicted to be a significant source of thermal noise for advanced detectors. Coatings must also be of low optical loss. - Main workpackage outcomes/long term aim: Definition of a low-mechanical-loss optical coating design/production process suitable for advanced detectors operating at either room or cryogenic temperatures - Groups involved: Institute for Gravitational Research, University of Glasgow Laboratoire des Matériaux Avancés, (LMA) Lyons AURIGA group, Laboratori Natzionali di Legnaro (+Leiden/Rome) Materials group, VIRGO, Perugia ESPCI, Laboratoire d'Optique, Paris

2. Timescales

3. Status of Glasgow Research Loss measurements at room T on SiO 2 /Ta 2 O 5 Set of coated samples (3” diameter by 1” thick) studied –(collaboration of the University of Glasgow with the LIGO Scientific Collaboration) Ta 2 O 5 component of the coating was doped with TiO 2 of varying percentages (supplied by LMA) Results suggest adding –any- TiO 2 reduces loss but there appears to be no strong correlation with amount of dopant. However exact percentage, and distribution, of dopant was unknown. Studies carried out at Glasgow (I. MacLaren) to quantify this. Loss Angle at 100 Hz of SiO 2 / Ta 2 O 5 doped with TiO 2 Loss angle

4. Studies of Ta 2 O 5 doped with TiO 2 Electron Energy Loss Spectroscopy (EELS) used to study doped and undoped coatings Able to image and measure the thickness of individual coating layers Dark layers are Ta 2 O 5 doped with TiO 2 Light layers are SiO 2 Surface Substrate

5. Studies of Ta 2 O 5 doped with TiO 2 Higher magnification imaging of layers The dark layer shows some strong speckle contrast Both dark and light layers are amorphous

6. Studies of Ta 2 O 5 doped with TiO 2 Light layers EELS Oxygen edge is strong at 532 eV Same O-K edge shape as for substrate –same chemical bonding in layers as in substrate Light coloured layers are SiO 2

7. Low energy - several elements detected –Several weak Ta edges –C from coating –Ti and O clearly there Could use one of the Ta edges together with Ti-L to calculate the Ta:Ti ratio Assuming Ti present as TiO 2 and Ta as Ta 2 O 5 then we find the percentage of Ti atoms present as (8.5+/-1.2)% Work ongoing to quantify other samples Studies of Ta 2 O 5 doped with TiO 2 Dark layers EELS

8. Map of TiO 2 in first sample studied Here, light layers are the doped Ta 2 O 5 layers The brighter the pixel, the more TiO 2 is present

9. Coatings at low temperature Working to study properties of coatings at low temperature *** (I.Martin, S.Reid, D. Crooks) Coatings to be applied to –thin fused silica samples (~1mm x 110  m x 5cm) –3” by 1” samples from previously Loss will be measured of coated samples as a function of temperature in two cryostats in Glasgow Initial measurements made at room temperature of thin substrates Fused silica substrate in cryostat FE model of fused silica substrate (M. Ahmed, N. Clarkson) Fused silica sample Thicker fused silica end

10. Characterisation of substrates - Room T Loss measured of thin silica cantilevers (I. Martin et al) Careful jointing of cantilever to clamped end piece can significantly reduce excess losses Will use these thin coated samples also to measure mechanical properties of coatings (E,  etc 

11. Studies of diffractive coatings Fused silica substrates with etched diffraction gratings fabricated by collaborators at the Universities of Hannover and Jena. Fused silica control sample - suspended under vacuum and preliminary measurements of mechanical loss made. (A. Cumming, A. Heptonstall) Coatings will be added by LMA Lyons over the next period.

12. Coatings on silicon Samples to be coated: –thin cantilevers –3” by 1” substrates Cantilever substrate loss characterised (submitted to PLA) – see talk by S. Reid Larger samples are currently under study (P. Murray, S. Reid, E. Chalkley) Substrates scheduled to be coated by LMA – ~January 2006

13. Status of Perugia Research See slides from Flavio Travasso

14. Status of Auriga group research The design of the cryogenic vessel for samples housing is complete Vacuum sealed copper cylinder Currently measurements of the Q factor of a substrate or substrate + coating with the shape of a slab are possible In future larger samples can be measured also (From J-P Zendri – see previous talk)

15. Next milestones/deliverables WP4