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 Daniel Friedrich GWADW Kyoto – May 17th, 2010 Coating thermal noise AdvLIGOAdvVirgo Future Past Present

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

4 Daniel Friedrich GWADW Kyoto – May 17th, 2010 Coating thermal noise Future Past Present LCGT: Proposed

5 Daniel Friedrich GWADW Kyoto – May 17th, 2010 Coating thermal noise Einstein Telescope: Goal sensitivity Future Past Present

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

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 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, (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, (2006) Novel ideas Future Past Present Stefan Goßler Tuesday 7pm

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

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

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

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 1064nm Future Past Present

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

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 1550nm Future Past Present

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

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

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

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

20 Daniel Friedrich GWADW Kyoto – May 17th, 2010 (99.8 ± Design/Experiment Opt. Express 17, (2009) PRL 104, (2010) Opt. Express 17, 163 (2009) (93 ± (99.08 ± CQG 23, 7297 (2006) Opt. Lett. 33, 3 (2008) Future Past Present

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, (2008) Thermo-optic

22 Daniel Friedrich GWADW Kyoto – May 17th, 2010 Coating thermal 1064nm Future Past Present ET

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, (2008)

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

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

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

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

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

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

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

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

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

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