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Kazuhiro Yamamoto Max-Planck-Institut fuer Gravitationsphysik (Albert-Einstein-Institut)

Coating thermal noise and cryogenic experiments. Kazuhiro Yamamoto Max-Planck-Institut fuer Gravitationsphysik (Albert-Einstein-Institut) Institut fuer Gravitationsphysik, Leibniz Universitaet Hannover. Kenji Numata University of Maryland NASA Goddard Space Flight Center.

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Kazuhiro Yamamoto Max-Planck-Institut fuer Gravitationsphysik (Albert-Einstein-Institut)

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  1. Coating thermal noise and cryogenic experiments Kazuhiro Yamamoto Max-Planck-Institut fuer Gravitationsphysik (Albert-Einstein-Institut) Institut fuer Gravitationsphysik, Leibniz Universitaet Hannover Kenji Numata University of Maryland NASA Goddard Space Flight Center 18 May 2010 Gravitational-Wave Advanced Detector Workshop @Hearton Hotel Kyoto, Kyoto, Japan

  2. 0.Abstract Review of coating thermal noise in cryogenic experiments (1) Temperature dependence of coating thermal noise (2) Examples of cryogenic experiments Not so new topics …. Please recover your knowledge about thermal noise !

  3. Contents 1. Introduction 2. Temperature dependence of mirror thermal noise 3. Examples of cryogenic experiments 4. Summary

  4. 1.Introduction Thermal noise of mirrors : Fundamental noise of interferometric gravitational wave detector around 100 Hz How do we reduce thermal noise ? One of the simplest solutions: Cooling mirrors Firstfeasibility study T. Uchiyama et al., Physics Letters A 242 (1998) 211.

  5. 1.Introduction At almost same time, there was drastic progress in research of mirror thermal noise. e.g. Coating thermal noise Y. Levin, Physical Review D 57 (1998) 659. Coating thermal noise is also a problem in other fields (frequency stabilization, quantum measurement). • How does thermal noise depend on temperature ? • Examples of cryogenic experiment

  6. 2. Temperature dependence of mirror thermal noise Amplitude of thermal noise is proportional to (T/Q)1/2. In general, Q(inverse number of magnitude of dissipation) depends on T(temperature). We must investigate how dissipation depends on temperature in cryogenic region.

  7. 2. Temperature dependence of mirror thermal noise • What kinds of thermal noise must be taken into account ? • Substrate Brownian noise • Substrate thermoelastic noise • Coating Brownian noise • Thermo-optic noise

  8. 2. Temperature dependence of mirror thermal noise (1) Substrate Brownian noise Structure damping (frequency independent) in substrate Fused silica can not be used. Sapphire or Silicon are good. Q value measurement T. Uchiyama et al., Physics Letters A 261 (1999) 5-11. R. Nawrodt et al., Journal of Physics: Conference Series 122 (2008) 012008. C. Schwarz et al., 2009 Proceedings of ICEC22-ICMC2008.

  9. 2. Temperature dependence of mirror thermal noise (2) Substrate thermoelastic noise Noise by temperature fluctuation in substrate via thermal expansion M. Cerdonio et al., Physical Review D 63 (2001) 082003.

  10. 2. Temperature dependence of mirror thermal noise (3) Coating Brownian noise (IBS Ta2O5/SiO2) Structure damping (frequency independent) in coating University of Tokyo Loss angle is almost independent of temperature. K. Yamamoto et al., Physical Review D 74 (2006) 022002.

  11. 2. Temperature dependence of mirror thermal noise (3) Coating Brownian noise Structure damping (frequency independent) in coating Peak at 20 K ? Glasgow University I. Martin et al., Classical and Quantum Gravity 25(2008)055005.

  12. 800 C 800 C 800 C 800 C 800 C 800 C 800 C 800 C 800 C 600 C 600 C 600 C 600 C 600 C 600 C 600 C 400C 400C 400C 400C 300C 300C 2. Temperature dependence of mirror thermal noise (3) Coating Brownian noise Structure damping (frequency independent) in coating Annealing suppresses (Ta2O5) peak. Glasgow University I. Martin et al., Einstein Telescope Meeting (March 2010).

  13. 2. Temperature dependence of mirror thermal noise (3) Coating Brownian noise Structure damping (frequency independent) in coating Goal temperature : below20 K It is assumed that loss is independent of temperature. Coating thermal noise is the most serious problem !

  14. 2. Temperature dependence of mirror thermal noise (4) Thermo-optic noise M. Evans et al., Physical Review D 78 (2008) 102003. Temperature fluctuation in coating Thermal expansion(a) Surface fluctuation: Thermoelastic noise Temperature coefficient of refractive index(b) Thickness fluctuation: Thermo-refractive noise Laser beam Summation of coating thermoelastic and thermo-refractive noise Coating Substrate V. B. Braginsky et al., Physics Letters A 312 (2003) 244. M.M. Fejer et al., Physical Review D 70 (2004) 082003. V. B. Braginsky et al., Physics Letters A 271 (2000) 303. 14 14

  15. 2. Temperature dependence of mirror thermal noise (4) Thermo-optic noise Material properties of substrate are known. Material properties of coating are not known well (at cryogenic temperature). Material properties of coating Thermal expansion and specific heat : Small at cryogenic temperature in general Small contribution Temperature coefficient of refractive index (b): Unknown at cryogenic temperature It is assumed that b is 10-5 /K (pessimistic assumption).

  16. 2. Temperature dependence of mirror thermal noise (4) Thermo-optic noise Thermo-optic noise is not so serious.

  17. 3. Examples of cryogenic experiments • Gravitational wave detector • Rigid cavity • Quantum measurement

  18. 3. Examples of cryogenic experiments • Gravitational wave detector CLIO : Current project (Japan) LCGT : Second generation project (Japan) ET : Third generation project (Europe) There are many talks about these projects.

  19. 3. Examples of cryogenic experiments • Gravitational wave detector CLIO group has already demonstratedreduction of mirror thermal noise (substrate thermoelastic) by cooling mirrors (T. Uchiyama’s talk on 18 May).

  20. 3. Examples of cryogenic experiments (2) Rigid cavity Reference for laser frequency stabilization Experimental check of Special Relativity (Modern version of Michelson-Morley or Kennedy-Thorndike experiments) Current best laser frequency stabilization with rigid cavity at room temperature is limited by thermal noise of mirrors. K. Numata et al., Physical Review Letters 93 (2004) 250602. Frequency stabilization with rigid cavity at 4 K should be about 30 times better than that at room temperature.

  21. 3. Examples of cryogenic experiments (2) Rigid cavity Current best laser frequency stabilization with rigid cavity at 3 K Universität Konstanz S. Seel et al., Physical Review Letters 78 (1997) 4741.

  22. 3. Examples of cryogenic experiments Best record at 3 K (2) Rigid cavity 2.5*10-15 Universität Konstanz NIST Best record at room temperature 4*10-16(limited by substrate Brownian noise) B.C. Young et al., Physical Review Letters 82 (1999) 3799.

  23. 3. Examples of cryogenic experiments (2) Rigid cavity Laser frequency stabilization with rigid cavity at cryogenic temperature should be better ! Allan deviation : 1*10-17(limited by coating Brownian noise) Current best record at 3 K : 2.5*10-15 Development is in progress (This is not a perfect list). Universität Konstanz, Humboldt-Universität zu Berlin, Heinrich-Heine-Universität Düsseldorf‎, Physikalisch-Technischen Bundesanstalt University of Tokyo (previous talk by Y. Aso)

  24. 3. Examples of cryogenic experiments (3) Quantum measurement Small mechanical oscillator on quantum ground state Cryogenic technique (~ 4K) and laser cooling (< 1 K) is necessary to reduce thermal noise. Oscillator must have small mechanical loss atlow temperature. High reflectance and low absorption are also necessary.

  25. 3. Examples of cryogenic experiments (3) Quantum measurement Oscillator made from coating material (Ta2O5/SiO2) low absorption ViennaUniversity Minimum energy : 104 times larger than ground state energy Limit : mechanical loss (f : 3*10-4 ~ 10-3) and reflectance S. Groeblacher et al., Europhysics Letters 81 (2008) 54003.

  26. 3. Examples of cryogenic experiments Minimum energy : 32 times larger than ground state energy (3) Quantum measurement Oscillator (Si3N4) with reflectivecoating (Ta2O5/SiO2) ViennaUniversity (f : 3*10-5) Next step : Evacuated 3He cryocooler S. Groeblacher et al., Nature Physics 5 (2009) 485.

  27. 4. Summary Development of cryogenic interferometric gravitational wave detector and research of coating thermal noise started on the end of 20th century. On the end of first decade of 21st century, (1) We know coating Brownian noise dominatesthermal noise at cryogenic temperature. (2) Reduction of mirror thermal noise (substrate thermoelastic) by cooling mirrors was demonstrated (CLIO). (3) Development of cryogenic cavity for frequency stabilization is progress (30 times better). (4) Coating thermal noise at cryogenic temperature is also hot topic in quantum measurement.

  28. Thank you for your attention !

  29. M.M. Fejer et al., Physical Review D 70 (2004) 082003.

  30. S. Groeblacher et al., Nature Physics 5 (2009) 485.

  31. electron beam evaporation magnetron sputtering R. Nawrodt et al., NewJournal of Physics 9 (2007) 225.

  32. 3. Practical consideration in cryogenic experiments A lot of details : W. Johnson’s talk on 18 May How much can temperature of mirror be ? • Heat load on mirror • Capacity of cryocooler • Heat conduction between mirror and cryocooler

  33. 3. Practical consideration in cryogenic experiments • Heat load on mirror Light absorption 300 K radiation In the case of future interferometric gravitational wave detector, heat load is about 1 W. In the case of table top Fabry-Perot cavity, heat load is less than 10 mW.

  34. 3. Practical consideration in cryogenic experiments (2) Capacity of cryocooler Second law of thermodynamics : Smaller capacity atlower temperature Pulse tube cryocooler : ~ 40 W at 45 K, ~ 1 W at 4 K Evacuated 3He cryocooler : ~ 100 mW at 1.2 K, ~10 mW at 0.7 K 3He-4He dilution cryocooler : ~ 1 mW at 0.3 K In the case of future interferometric gravitational wave detector, cryocooler temperature is above 4 K. In the case of table top Fabry-Perot cavity, cryocooler temperature is above 1 K.

  35. 3. Practical consideration in cryogenic experiments (3) Heat conduction between mirror and cryocooler Crystal (Sapphire or Silicon) Thermal conductivity : ~ 10000 W/m/K around 20 K Temperature dependence : T3 Small mechanical dissipation Pure metal (Aluminum or Copper) Thermal conductivity : ~ 10000 W/m/K around 10 K Temperature dependence : T1 Large mechanical dissipation

  36. 3. Practical consideration in cryogenic experiments (3) Heat conduction between mirror and cryocooler In the case of future interferometric gravitational wave detector, mirror must be suspended by crystal fiber (because of small mechanical dissipation). Mirror at 20 K : possible Temperature dependence of thermal conductivity: T3 Below 20 K : Difficult

  37. 2. Temperature dependence of mirror thermal noise (4) Thermo-optic noise Coating thermoelastic noise Temperature fluctuation in coating causes extra vibration due to difference of material. Correlation (same origin : temperature fluctuation) V. B. Braginsky et al., Physics Letters A 312 (2003) 244. M.M. Fejer et al., Physical Review D 70 (2004) 082003.

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