1. 1 Daniel Friedrich GWADW Kyoto – May 17th, 2010 Waveguide grating mirrors Insights from the inside Future Past Present Daniel Friedrich, Michael Britzger, Karsten Danzmann and Roman Schnabel Frank Brückner, Stefanie Kroker, Ernst-Bernhard Kley and Andreas Tünnermann Max Planck Institute for Gravitational Physics (AEI Hannover), Leibniz Universität Hannover Institute of Applied Physics, Friedrich-Schiller-Universität Jena

2. 2 Daniel Friedrich GWADW Kyoto – May 17th, 2010 Coating thermal noise http://wwwcascina.virgo.infn.it/advirgoLIGO-M060056-v1 AdvLIGOAdvVirgo Future Past Present

3. 3 Daniel Friedrich GWADW Kyoto – May 17th, 2010 Coating thermal noise GEO-HF Future Past Present GEO-HF logbook, page 60

4. 4 Daniel Friedrich GWADW Kyoto – May 17th, 2010 Coating thermal noise http://gw.icrr.u-tokyo.ac.jp/lcgt/ Future Past Present LCGT: Proposed

5. 5 Daniel Friedrich GWADW Kyoto – May 17th, 2010 Coating thermal noise Einstein Telescope: Goal sensitivity Future Past Present http://www.et-gw.eu

6. 6 Daniel Friedrich GWADW Kyoto – May 17th, 2010 The 22nd century Future Past Present

7. 7 Daniel Friedrich GWADW Kyoto – May 17th, 2010 Addressing coating Brownian noise Material research e.q. mechanical loss φ Reduction of coating thickness d Cryogenic temperature T Larger beam size r 0 Future Past Present G. Harry et al., CQG, 19, 897 (2002)

8. 8 Daniel Friedrich GWADW Kyoto – May 17th, 2010 Corner reflectors V. B. Braginski and S. P. Vyatchanin Phys. Lett. A 324, 345 (2004) The ANU coating-free mirror S. Goßler et al. Phys. Rev A 76, 053810 (2007) Cavity as mirror F. Ya. Khalili Phys. Lett. A 334, 67 (2005) Coating-free corner reflector G. Cella and A. Giazotto Phys. Rev. D, 74 042001 (2006) Novel ideas Future Past Present Stefan Goßler Tuesday 7pm

9. 9 Daniel Friedrich GWADW Kyoto – May 17th, 2010 Waveguide grating mirrors Rigorous Coupled Wave Analysis (RCWA) www.unigit.com Future Past Present Broadband waveguide grating mirrors @ 1064nm A. Bunkowski et al. Class. Quantum Grav. 23, 7297 (2006)

10. 10 Daniel Friedrich GWADW Kyoto – May 17th, 2010 On the road to coating-free mirrors Future Past Present Single-layer Monolithic Quasi-Monolithic

11. 11 Daniel Friedrich GWADW Kyoto – May 17th, 2010 Silica Tantala Single-layer WGG @ 1064nm Future Past Present

12. 12 Daniel Friedrich GWADW Kyoto – May 17th, 2010 Grating size: 7.5mm*7.5mm Cavity Length = (0.495±0.001)m Beam radius  100  m Finesse  650 Highest reflectivity = (99.08±0.05)% Entire area: R>96% Single-layer WGG @ 1064nm Future Past Present

13. 13 Daniel Friedrich GWADW Kyoto – May 17th, 2010 Monolithic WGG @ 1550nm Crystalline Si Future Past Present

14. 14 Daniel Friedrich GWADW Kyoto – May 17th, 2010 silica mask on a Si-substrate 1. anisotropic etching 2. resist removal 3. passivation of sidewalls 4. isotropic etching 5. BOSCH®- process 6. removal of passivated layer Monolithic WGG @ 1550nm Future Past Present

15. 15 Daniel Friedrich GWADW Kyoto – May 17th, 2010 Monolithic WGG @ 1550nm Future Past Present

16. 16 Daniel Friedrich GWADW Kyoto – May 17th, 2010 Monolithic WGG @ 1550nm Future Past Present Grating size: 7.5mm*13mm Cavity Length = (24±0.5)mm Beam radius  50  m Finesse  3000 Highest reflectivity = (99.8±0.01)% Area of 2mm*2mm: R= (99.77±0.01)%

17. 17 Daniel Friedrich GWADW Kyoto – May 17th, 2010 Quasi-Monolithic WGG @ 1550nm Future Past Present

18. 18 Daniel Friedrich GWADW Kyoto – May 17th, 2010 Bonding Coating Quasi-Monolithic WGG @ 1550nm Future Past Present 1st try Not done yet

19. 19 Daniel Friedrich GWADW Kyoto – May 17th, 2010 Quasi-Monolithic WGG @ 1550nm R=(93±0.5)% Future Past Present optimal design

20. 20 Daniel Friedrich GWADW Kyoto – May 17th, 2010 (99.8 ± 0.01)% @1550nm Design/Experiment Opt. Express 17, 24334 (2009) PRL 104, 163903 (2010) Opt. Express 17, 163 (2009) (93 ± 0.5)% @1550nm (99.08 ± 0.05)% @1064nm CQG 23, 7297 (2006) Opt. Lett. 33, 3 (2008) Future Past Present

21. 21 Daniel Friedrich GWADW Kyoto – May 17th, 2010 Coating thermal noise Brownian = Thermoelastic + Thermorefractive TT Future Past Present  thermal fluctuations  thermal energy T G. Harry et al., CQG, 19, 897 (2002) M. Evans et al., Phys. Rev. D 78, 102003 (2008) Thermo-optic

22. 22 Daniel Friedrich GWADW Kyoto – May 17th, 2010 Coating thermal noise @ 1064nm Future Past Present ET-021-09

23. 23 Daniel Friedrich GWADW Kyoto – May 17th, 2010 Coating thermal noise (roughly) Brownian Thermoelastic Thermorefractive Future Past Present …  8 uppermost double layer dominate … coating thickness … coating thickness & mechanical loss M. Evans et al., Phys. Rev. D 78, 102003 (2008)

24. 24 Daniel Friedrich GWADW Kyoto – May 17th, 2010 WG thermal noise (roughly) Future Past Present Brownian Thermoelastic Thermorefractive … strongly depends on the design … coating thickness … coating thickness & mechanical loss

25. 25 Daniel Friedrich GWADW Kyoto – May 17th, 2010 Brownian noise estimates of WGs T=18K Contribution from R. Nawrodt Dedicated Q-factor measurements are on the way Future Past Present SiO2/Ta2O5  6  m Ta2O5  0.4  m Si  1.5  m Si-substrate Theoretical: Experimental: Christian Schwarz Wednesday 5:20pm Brownian … coating thickness & mechanical loss

26. 26 Daniel Friedrich GWADW Kyoto – May 17th, 2010 Future Past Present High coupling efficiency (±1T  33%) Low coupling efficiency (±1T  1%) Thermorefractive noise of WGs Thermorefractive … strongly depends on the design

27. 27 Daniel Friedrich GWADW Kyoto – May 17th, 2010 Future Past Present Thermorefractive noise of WGs  t=3nm →  Φ  50deg  t=30nm →  Φ  50deg

28. 28 Daniel Friedrich GWADW Kyoto – May 17th, 2010 Optical thickness TT Future Past Present Tantala Silica Phase change with temperature

29. 29 Daniel Friedrich GWADW Kyoto – May 17th, 2010 Evanescent coupling Optical thickness TT Future Past Present Tantala Silica Phase change with temperature

30. 30 Daniel Friedrich GWADW Kyoto – May 17th, 2010 Evanescent coupling Optical thickness TT Lateral expansion (many effects) Future Past Present Tantala Silica Phase change with temperature

31. 31 Daniel Friedrich GWADW Kyoto – May 17th, 2010 Thermal noise estimates @ 1064nm Future Past Present Material properties for ML and WG assumed to be the same 0.8  m 6m6m

32. 32 Daniel Friedrich GWADW Kyoto – May 17th, 2010 Conclusions on single layer WG Future Past Present Q: Brownian noise… A: The reduced thickness is an advantage Q: Thermoelastic noise… A: Not yet investigated, but the reduced thickness should be an advantage Q: Thermorefractive noise… A: Presented model suggests that optimal designs/materials are required

33. 33 Daniel Friedrich GWADW Kyoto – May 17th, 2010 Thoughts about monolithic WG Future Past Present Q: Brownian noise… A: Monocrystaline structures are promising in terms of low mechanical loss Q: Thermoelastic noise… A: Modeling will be complex due to the sophisticated structure Q: Thermorefractive noise… A: Silicon allows for parameter tolerant designs. Hence, it will be much less sensitive to temperature fluctuations.

34. 34 Daniel Friedrich GWADW Kyoto – May 17th, 2010 WGG @ Glasgow prototype Looking forward to october 2010 M. Edgar et al. Opt. Lett. 34, 3184 (2009) Future Past Present

35. 35 Daniel Friedrich GWADW Kyoto – May 17th, 2010 Modeling thermal noise (Model the structure, optimize designs, …) Work to be done Direct thermal noise measurement (Will put it to the test) Test mass size/optical quality (Scattering, further treatment, bonding, …) Future Past Present

36. 36 Daniel Friedrich GWADW Kyoto – May 17th, 2010 Thank you

37. 37 Daniel Friedrich GWADW Kyoto – May 17th, 2010 ‚Uninvited guests‘ ? xx １． All phase shifts cancel ２． Numerical results agree ３． Dynamical effects unlikely

38. 38 Daniel Friedrich GWADW Kyoto – May 17th, 2010 Thermal noise estimates R. Nawrodt et al. New Journal of Physics 9, 225 (2007) Grating structure does not „destroy“ high Q-factor of substrate, but…

39. 39 Daniel Friedrich GWADW Kyoto – May 17th, 2010 silicon(n=3.5), λ=1550nm, d=700nm, TM-polarization Si Monolithic WGG @ 1550nm

40. 40 Daniel Friedrich GWADW Kyoto – May 17th, 2010 Monolithic WGG @ 1550nm  130MHz Contribution from R. Nawrodt

41. 41 Daniel Friedrich GWADW Kyoto – May 17th, 2010 d=690nm, s=400nm Single-layer WGG @ 1064nm

42. 42 Daniel Friedrich GWADW Kyoto – May 17th, 2010 Quasi-Monolithic WGG @ 1550nm