Thermal noise @ cryogenic temperatures

1. Thermal noise @cryogenic temperatures Janyce Franc R. Flaminio, N. Morgado LMA-CNRS WP2 meeting 27-02-09

2. Contents • Introduction • State of the art @ room temperature • State of the art @ cryogenic temperature • Conclusion and future work J. Franc et al. - 27th february 2009

3. Introduction 1. Headlines of ET Project 2. Thermal Noises considered

4. The headlines for E.T. project LMA in WP2 : THE TASK Definition of substrate and coating properties at low temperatures • Document describing the status of the art of our knowledge • Mirror Thermal Noises • Status of the art @ 300 K • Status of the art @ low temperature Tasks have been defined during the first meeting @ Cascina in 25/11/08 J. Franc et al. - 27th february 2009

5. Summary of thermal noises J. Franc et al. - 27th february 2009

6. Aim of presentation • Describe present status of the document • Discuss considered parameters • , , C, a, , σ, n, Y • State of the art of all parameters of substrates and coatings • To draw up a synthetic approach at room temperature and cryogenic temperature J. Franc et al. - 27th february 2009

7. Room Temperature 1. Parameters values @ 300K 2. Simulation with ‘standard coatings’ 3. Other possible coatings

8. Remind the standard coatings results @ 300K Large dependency on substrate? Data confusion… Coating parameters different from bulk parameters J. Franc et al. - 27th february 2009

9. Remind the substrates results at 300K Different results… J. Franc et al. - 27th february 2009

10. Simulations @ 300K SiO2-Ta2O5 coatings : 17 doublets High thermoelastic noise @ low frequencies Limited by coating brownian noise High thermoelastic noise @ low frequencies J. Franc et al. - 27th february 2009

11. Other coatings parameters @ 300K Low brownian noise… Promising coating? Dependency on substrates Parameters are not the same for bulk and coating!! Large variations of parameters such as a and  J. Franc et al. - 27th february 2009

12. Simulation : some coatings @ 300K SiO2-TiO2 : HB 13 HBB SiO2-Nb2O5 : HB 14 HBB SiO2-ZrO2 :HB 17 HBB Al2O3-TiTa2O5 : HB 24 HBB Al2O3-ZrO2 : HB 22 HBB High thermo-elastic noise For the moment, the thermoelastic and thermorefractive noises are two independant noises : COMPENSATION NOT CONSIDERED Advantage for SiO2-Ti:Ta2O5 Promising coatings? Al2O3-TiTa2O5 SiO2-Nb2O5 BUT this study considered only the thermal noise aspect … LATER, the report will include also the optical absorption point of view J. Franc et al. - 27th february 2009 Coatings realized for 6ppm @ 1064 nm

13. Cryogenic Environment 1. Cryogeny : favourable conditions 2. Parameters values 3. Missing parameters and future? 4. The project for LMA

14. The favourable conditions @ cryogenic temperature • Reduce Thermal Noise by decreasing the temperature by 30 (300 k -> 10 k) • Thermal parameters : • Thermal Conductivity goes up to a maximum value • Heat Capacity decreases • Thermal Expansion Coefficient decreases (and crosses 0) • GOAL • FIND new materials with best parameters J. Franc et al. - 27th february 2009

15. Evolution of thermal parameters at low temperature : the case of Si J. Franc et al. - 27th february 2009

16. State of the art for substrates @ cryogenic temperatures Can generate High Thermo Elastic Noise J. Franc et al. - 27th february 2009

17. Thermo-elastic noise due to low specific heat Substrate Brownian noise Thermo-elastic noise SimulationsSubstrates thermal noise Advantage for Sapphire and Silicon substrate at ~10K J. Franc et al. - 27th february 2009

18. Simulations Silicon substrate @ diff. Temp. Important fluctuation from 4K to 30K… …more than a 10 ratio! Data from MPDB http://www.jahm.com/ …With Si = 0.5 10-9 J. Franc et al. - 27th february 2009

19. State of the art for coatings @ cryogenic temperatures HfO2 : best promising high index coating? A lot of missing parameters… same values taken at cryo and 300K J. Franc et al. - 27th february 2009

20. Missing parameters and future • C, , , a are essential parameters to forecast the total thermal noise. • A lot of missing parameters for coatings @ cryogenic temperature • Difficult to simulate correctly the thermal noise of coatings • More measurements on coatings are needed J. Franc et al. - 27th february 2009

21. Simulations @ 10KTotal thermal noise SiO2-Ta2O5 coatings : 17 doublets Some parameters of Ta2O5 are at 300K (unkown at low temperature) J. Franc et al. - 27th february 2009

22. Conclusion and future works

23. Developed new promising coatings for low temperatures • According to the state of the art at cryogenic temperature and the influence on thermal noise : • HfO2 mechanical losses are encouraging but any other parameters are known • Al2O3 was a good candidate for low index coating at room temperature… why not at 10K? • We can not decide between silicon and sapphire at 10K • New doped materials? J. Franc et al. - 27th february 2009

24. Cryogenic installation @ LMA • More measurements on coatings at low temperature are needed • Cryocooler project inside LMA to speed up test of different materials (see positive experience with Perugia/Q bench installed at LMA) • A cryostat for two measurements : • Measure of Q factor • Measure of optical absorption J. Franc et al. - 27th february 2009