1. Janyce Franc-Kyoto-GWADW1 Simulation and research for the future ET mirrors Janyce Franc, Nazario Morgado, Raffaele Flaminio Laboratoire des Matériaux Avancés CNRS Villeurbanne, FRANCE Tuesday 18th May 2010

2. Janyce Franc-Kyoto-GWADW2 Contents Mirror Thermal Noises Solutions to reduce Mirror Thermal Noise –Find New materials –Cool down mirrors –Use Laguerre-Gauss modes Mirrors for ET Coating research activities at LMA

3. Janyce Franc-Kyoto-GWADW3 Mirror thermal noises and ET w=6 cm Infinite mirror Unless otherwise specified ET Adv. Virgo

4. Janyce Franc-Kyoto-GWADW4 Coating Brownian noise Reduce losses by new coating materialsReduce the temperature Increase the Ysub by changing the material substrate Change the beam shape and size

5. Janyce Franc-Kyoto-GWADW5 Coating materials TiTa 2 O 5 TiO 2 Nb 2 O 5 ZrO 2 SiO 2 Al 2 O 3  2 10 -4 6.3 10 -3 4.6 10 -4 5.9 10 -4 0.5 10 -4 2.4 10 -4  (kg.m -3 ) 642542304590600022003700  (W.m -1.K -1 ) 0.60.4511.090.53.3 C (J. K -1.Kg -1 )26913059026746310  (K -1 ) 3.6 10 -6 0.5 10 -6 5.8 10 -6 10.3 10 -6 0.51 10 -6 8.4 10 -6  (dn/dT) 14 10 -6 -1.8 10 -4 1.43 10 -5 10 10 -5 8 10 -6 1.3 10 -6 Y (GPa)1402908020060210  0.230.280.20.270.170.22 n2.062.32.322.151.451.63 N.B. Parameters available in J.Franc et al. ET-02109

6. Janyce Franc-Kyoto-GWADW6 SiO 2 -Ti:Ta 2 O 5 coating offers the best result SiO 2 -Nb 2 O 5 is also a good candidate (but absorption slightly higher) Coating materials N.B. Parameters available in J.Franc et al. ET-02109 Comparison of different coatings with same transmission (6 ppm)

7. Janyce Franc-Kyoto-GWADW7 Substrate materials (300K) Silica remains the best substrate materials at 300K Also better from an optical point of view And available in large pieces (just need to increase budget) TE Noise limits the Si and Sapphire TN

8. Janyce Franc-Kyoto-GWADW8 Low temperature: substrate materials Similar level for Silicon and Sapphire. Silicon is promising because of its interest in microelectronics industry. SiO 2 is unsuitable 10K

9. Janyce Franc-Kyoto-GWADW9 Low temperature: Silicon * Band-to-band absorption reported in literature (Green et al., 1995) * The total absorption might be higher due to : - Impurities - Residual conductivity At 1550 nm impurities expected to be dominant * The absorption have to be precisely determined! * Work in progress at LMA * NB Only 8’’ diameter silicon wafers with the best optical quality are available so far. Silicon absorption M. Green and M. Keevers, Optical properties of intrinsic Silicon @ 300K, Progress in Photovoltaic research and Applications, Vol. 3, 189- 192 (1995)

10. Janyce Franc-Kyoto-GWADW10 Low temperature: Silicon Large sensitivity variation vs Temperature! Good results obtained at 4-20K 30K must be avoided No real interest in working at 18 K because of Substrate Brownian noise Coating losses (see next slide)

11. Janyce Franc-Kyoto-GWADW11 Low temperature: Coating losses I. Martin et al. Class. Quantum Grav. 25 (2008) 055005 18K 10K

12. Janyce Franc-Kyoto-GWADW12 Beam shape (and size) Advantages : -Best power distribution on the mirror surface -Lower Thermal Noise -Lower Thermal Lensing To reduce Thermal noise the beam shape and size can be changed.

13. Janyce Franc-Kyoto-GWADW13 Beam shape: thermal noise reduction Coating Brownian Noise Substrate Brownian Noise Substrate TE noise (frequency dependent) TEM00/LG33 Infinite mirror 1.71.91.06-1.8 TEM00/LG33 Finite mirror (Ø:45cm, h:30 cm) 1.61.41.08-1.86 LG55 does not demonstrate better results ET NOTE with all the results: soon available

14. Janyce Franc-Kyoto-GWADW14 Solutions for ET Low frequency ITFHigh frequency ITF Temperature10K300K Mirror sizeØ : 45 cm H : 30 cm Ø : 62 cm H : 30 cm SubstrateSiliconSilica Wavelength1550 nm1064 nm CoatingTi:Ta 2 O 5 & SiO 2 Phi coat2.10 -4 & 0.5.10 -4 Reference : S. Hild et al., CQG, 2010, 27, 015003

15. Janyce Franc-Kyoto-GWADW15 At low frequency : 45 cm diameter + silicon + 10K+ TEM00 is enough At higher frequency : 62 cm diameter + silica + 300K+ LG33 is possible Solutions for ET

16. Janyce Franc-Kyoto-GWADW16 Study of coating losses at LMA Mechanical losses measurement at LMA Coating deposit chambers at LMA * Ta 2 O 5 * Ti:Ta 2 O5 * SiO2 1. The coating are deposited on silica cantilevers in the same coater used for the Virgo mirrors. 2. The Q of the cantilever is measured before coating deposition (200 000-300 000) => limitation 3. The Q of the cantilever after deposition is measured and we can deduce the coating loss angle. 4. Good system for Tantala. Not enough sensitivity for silica film.

17. Janyce Franc-Kyoto-GWADW17 Q of silica layers Welded cantilever (frequency of vibration in Hz) 1 st mode730 000 (50 Hz) 2 nd mode720 000 (300 Hz) 3 rd mode1 250 000 (800 Hz) Silica cantilever Silica block Cantilever welded to Silica block Silica losses (1st mode) 1st cantilever4.5 (+/- 1) 10 -5 2 nd cantilever4.2 (+/- 1) 10 -5 In accordance with the reported values of 5.10 -5. Need more tests. The tests with classical cantilever did not permit to measure this value. Collaboration INFN Perugia (H. Vocca)

18. Janyce Franc-Kyoto-GWADW18 Q of high index materials Preliminary studies – Need more measurement before to conclude! MaterialsLosses angles Ta 2 O 5 3 10 -4 Ti:Ta 2 O 5 2 10 -4 Nb 2 O 5 4.6 10 -4 Measurements generally done for a 500 nm thick film. BUT some variation observed when different thickness are measured…

19. Janyce Franc-Kyoto-GWADW19 Q of multilayer coatings 1. Q of multilayer coating can be deduced from losses of materials and coating formula. 2. First measurements showed larger losses in multilayer coatings than foreseen. Thought to be due to defects in the coating coming from poor cantilever surface quality. 3. Recently, mechanical losses of different multilayer coatings with no defects have been measured and confirm larger losses than expected. 4. More studies are needed CoatingThickness (nm)  Coating measured  coating theoretical  doped-tantala deduced 0.817H(1.0736L0.8 828H)12 0.0851L 38592.5 10 -4 1.32 10 -4 4.2 10 -4 0.87B(HB)20HBB52223.4 10-41.34 10 -4 5.8 10 -4 Some preliminary results :

20. Janyce Franc-Kyoto-GWADW20 Conclusions - By combining different solutions (larger beams, LG modes, Silicon and low T) the ET sensitivity seems achievable. - But a strong R&D program is necessary to: reduce coating losses evaluate silicon optical properties develop LG interferometry ……. - Study of coating losses at LMA with cantilevers: Confirm low losses for silica mono layers Shows some excess of losses in thick coatings to be better investigated

21. Janyce Franc-Kyoto-GWADW21 At low frequency : 45 cm diameter + silicon + 10K+ TEM00 is enough At higher frequency : 62 cm diameter + silica + 300K+ LG33 is possible Solutions for ET

22. Janyce Franc-Kyoto-GWADW22 Low temperature: other coating noises?  =6 10 -5 (K -1 ) Thermal Exp. coefficient limits sensitivity if value 20 times larger than value @ 300 K At low temperature a lot of the coating parameters are unknown. The thermoelastic (  coef.) and thermorefractive (  coef.) noises can not be evaluated. Question: how large should  and  to become limited by TE and TR noises? Answer: -  = 6 10 -5 K -1 20 times larger than at 300 K! -  = 25 10 -4 K -1 200 times larger than at 300 K! Unlikely