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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. Simulation and research for the future ET mirrors. Contents. Mirror Thermal Noises Solutions to reduce Mirror Thermal Noise Find New materials

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Simulation and research for the future ET mirrors

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

  2. 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 Janyce Franc-Kyoto-GWADW

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

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

  5. Coating materials N.B. Parameters available in J.Franc et al. ET-02109 Janyce Franc-Kyoto-GWADW

  6. Coating materials Comparison of different coatings with same transmission (6 ppm) SiO2-Ti:Ta2O5 coating offers the best result SiO2-Nb2O5 is also a good candidate (but absorption slightly higher) N.B. Parameters available in J.Franc et al. ET-02109 Janyce Franc-Kyoto-GWADW

  7. Substrate materials (300K) TE Noise limits the Si and Sapphire TN 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) Janyce Franc-Kyoto-GWADW

  8. Low temperature: substrate materials 10K SiO2 is unsuitable Similar level for Silicon and Sapphire. Silicon is promising because of its interest in microelectronics industry. Janyce Franc-Kyoto-GWADW

  9. 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) Janyce Franc-Kyoto-GWADW

  10. 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) Janyce Franc-Kyoto-GWADW

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

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

  13. Beam shape: thermal noise reduction LG55 does not demonstrate better results ET NOTE with all the results: soon available Janyce Franc-Kyoto-GWADW

  14. Solutions for ET Reference : S. Hild et al., CQG, 2010, 27, 015003 Janyce Franc-Kyoto-GWADW

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

  16. Study of coating losses at LMA Coating deposit chambers at LMA 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. * Ta2O5 * Ti:Ta2O5 * SiO2 Mechanical losses measurement at LMA Janyce Franc-Kyoto-GWADW

  17. Q of silica layers Cantilever welded to Silica block Silica block Silica cantilever Collaboration INFN Perugia (H. Vocca) 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. Janyce Franc-Kyoto-GWADW

  18. Q of high index materials Measurements generally done for a 500 nm thick film. BUT some variation observed when different thickness are measured… Preliminary studies – Need more measurement before to conclude! Janyce Franc-Kyoto-GWADW

  19. 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 Some preliminary results : Janyce Franc-Kyoto-GWADW

  20. 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 Janyce Franc-Kyoto-GWADW

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

  22. Low temperature: other coating noises? 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! - b= 25 10-4 K-1 200 times larger than at 300 K! Unlikely =6 10-5 (K-1) Thermal Exp. coefficient limits sensitivity if value 20 times larger than value @ 300 K Janyce Franc-Kyoto-GWADW

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