1. A. Bunkowski Nano-structured Optics for GW Detectors 1 A.Bunkowski, O. Burmeister, D. Friedrich, K. Danzmann, and R. Schnabel in collaboration with T. Clausnitzer, S. Fahr, E.-B. Kley, and A. Tünnermann Institute of Applied Physics, Jena Max-Planck-Institut Für Gravitationsphysik (Albert-Einstein-Institut) Universität Hannover

2. A. Bunkowski Nano-structured Optics for GW Detectors 2 Outline Summary of: All-reflective Interferomtry (with multilayer coatings) Outlook to: High reflective diffractive structures (without multilayer coatings)

3. A. Bunkowski Nano-structured Optics for GW Detectors 3 Motivation #1 Interferometers beyond LIGOII (MW of power) Transmission  Absorption  Thermal problems All-reflective interferometers: Allow opaque test mass materials New interferometer topologies

4. A. Bunkowski Nano-structured Optics for GW Detectors 4 MI with all-reflective beamsplitter

5. A. Bunkowski Nano-structured Optics for GW Detectors 5 What kind of gratings? Coating below Coating on top Period defines # of orders & direction Grating equation: d>> scalar approach d rigorous theories (RCWA, Modal method) d<< effective medium theories (ETM)

6. A. Bunkowski Nano-structured Optics for GW Detectors 6 1R Cavity couplers 1st order Littrow2nd order Littrow Need high efficiency (which is hard to achieve) Only low efficiency (3 ports are more Complicated) 99.62% achieved (Finesse of 1580) A. Bunkowski et al, Applied Optics (in press) http://ao.osa.org/upcoming_pdf.cfm?id=66481 Input 0R1R Input 0R2R Input Appl. Opt. (in press)

7. A. Bunkowski Nano-structured Optics for GW Detectors 7 Cavity couplers 1st order Littrow2nd order Littrow Need high efficiency (which is hard to achieve) Only low efficiency (3 ports are more Complicated) A. Bunkowski et al, Applied Optics (in press) http://ao.osa.org/upcoming_pdf.cfm?id=66481 99.62% achieved (Finesse of 1580) A. Bunkowski et al, Applied Optics (in press) http://ao.osa.org/upcoming_pdf.cfm?id=66481 Input 0R1R Input 0R2R Input 1R

8. A. Bunkowski Nano-structured Optics for GW Detectors 8 3-port couplers A. Bunkowski et al, Opt. Lett. 30, 1183 (2005) R. Schnabel et al, Opt. Lett. 31 658 (2006) A. Bunkowski et al, Opt. Lett. 29, 2342 (2004)  A. Bunkowski et al, Opt. Lett. (in press) http://ol.osa.org/upcoming_pdf.cfm?id=69970

9. A. Bunkowski Nano-structured Optics for GW Detectors 9 Angle resolved scattering -1 st +1 st diffraction orders due to e-beam writing errors background due to statistical roughness „Variable shaped beam“ apertures shaped beam electron beam work field stitching E-beam exposure

10. A. Bunkowski Nano-structured Optics for GW Detectors 10 Grating beneath coating Small fill factor same diffraction efficiency systematical errors reduced statistical background reduced groove depth 40nm fill factor 50% T. Clausnitzer et. al., Optics Express, 13, 4370 (2005)

11. A. Bunkowski Nano-structured Optics for GW Detectors 11 diffraction efficiency 1.5%  0.03% systematical errors statistical background Large fill factor groove depth 40nm fill factor 82% Grating beneath coating II T. Clausnitzer et al, Optics Express, 13, 4370 (2005)

12. A. Bunkowski Nano-structured Optics for GW Detectors 12 Conclusion #1 Summary: High quality all-reflective components Demonstration of new cavity coupling concept Reduction of scattering loss Outlook: Further reduction of loss Scale to large test mass Suspended 10 m all-reflected cavity to be built in Glasgow later this year

13. A. Bunkowski Nano-structured Optics for GW Detectors 13 Motivation #2 S. Penn et.al, LIGO-P050049-00-R (2005) Several fundamental noise sources as currently estimated for advanced LIGO:

14. A. Bunkowski Nano-structured Optics for GW Detectors 14 Beating Coating Noise The high refractive material tantala (Ta 2 O 5 ) has been identified to be the main source of coating thermal noise. Some ideas so far: Less tantala in stack  Innocenzo Pinto’s talk Doping of tantala with TiO 2  Harry et al, Appl. Opt. 45, 1569 (2006) Total internal reflection  Adalberto Giazotto’s talk  V. Braginsky and S. Vyatchanin, Phys. Lett. A 324, 345 (2004) Double mirrors:  F. Ya. Khalili, Phys. Lett. A 334, 67 (2005) Substrate Coating stack AR-Coating stack

15. A. Bunkowski Nano-structured Optics for GW Detectors 15 Coating Thermal Noise Grating waveguide reflector AR-Coating stack Substrate Another approach: Substrate Coating stack

16. A. Bunkowski Nano-structured Optics for GW Detectors 16 Grating waveguide Structures see for example: Sharon et al, J. Opt. Soc. Am. A, 14 (1997) n Low (substrate) n High Interfere destructively 100% reflection Total internal reflection 0R 1T 0T waveguide (Simplified ray picture)

17. A. Bunkowski Nano-structured Optics for GW Detectors 17 Narrow reflection peak Liu et al,Opt. Lett. 23, 1556 (1998)

18. A. Bunkowski Nano-structured Optics for GW Detectors 18 Design width of reflection peak d: period g: groove depth r: ridge width s: film thickness r/d: fill factor g n=1.45 (substrate) d s n=2.04 r Fill factor g [µm] [%]

19. A. Bunkowski Nano-structured Optics for GW Detectors 19 Design width of reflection peak Fill factor g [µm] [%] X 1-R

20. A. Bunkowski Nano-structured Optics for GW Detectors 20 Broadband mirror for 1550nm Mateus et al, IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 16, NO. 7, JULY 2004 Si SiO 2 Poly-Si 0dB  reference mirror with R=98.5%

21. A. Bunkowski Nano-structured Optics for GW Detectors 21 Conclusion #2 Summary: High reflectivity is possible with single layer Outlook: Check fabrication tolerances, finite size effects… Design, build and test gratings Think of better suited wave guide structures

22. A. Bunkowski Nano-structured Optics for GW Detectors 22 great, greater, grating