1/16 Nawrodt, Genoa 09/2009 An overview on ET-WP2 activities in Glasgow R. Nawrodt, A. Cumming, W. Cunningham, J. Hough, I. Martin, S. Reid, S. Rowan ET-WP2 Workshop, Genoa/Italy 15 th September 2009

2/16 Nawrodt, Genoa 09/2009 Content design study report mirror thermal noise calculation size estimate of the mirror novel concept: nano-structured optics (surface loss of silicon) suspension thermal noise experimental work supporting the ET design next steps

3/16 Nawrodt, Genoa 09/2009 Mirror thermal noise review of mirror thermal noise revealed a coating Brownian noise limited regime (see talk J. Franc or ET ) 20 K Si(111) standard dielectric coating (Ta 2 O 5 / SiO 2 )

4/16 Nawrodt, Genoa 09/2009 Mirror thermal noise reason for high coating Brownian noise is the increasing mechanical loss of the amorphous coating materials

5/16 Nawrodt, Genoa 09/2009 Size estimate further reduction by means of larger beam radius unrealistic beam radius needed combination of upscaling and better coatings needed max. beam radius determined by availability of silicon (dia. 20 inch) 18 K

6/16 Nawrodt, Genoa 09/2009 Mirror thermal noise What coating loss is needed and how can it be achieved? international coating research is ongoing, but so far we don’t have a full understanding of the origin of this loss 4×10 -4 for Ta 2 O 5 2×10 -4 for SiO 2 example

7/16 Nawrodt, Genoa 09/2009 Monolithic Waveguide Mirror Si 500 nm aim: no amorphous coating materials needed  low mechanical loss  low thermal noise high reflectivity was shown (> 99.8%) combined use at 1550 nm could reduce optical absorption and would thus reduce problems arising for the heat extraction surface area is roughly doubled by the structure  surface loss will contribute stronger

8/16 Nawrodt, Genoa 09/2009 Surface Loss of Silicon A thin lossy surface layer is assumed: If the structure is thin only the top and bottom surface contribute: Following Gretarsson and Harry (1999): with the dissipation depth d s which is obtained from measurements with oscillators and at temperatures where the surface loss will dominate (thin samples at low temperatures).  … displacement field

9/16 Nawrodt, Genoa 09/2009 Surface Loss of Silicon mechanical loss obtained from different published papers for silicon oscillators with small dimensions (T<18 K) in pure bending  =  sub × d s = 0.5 pm loss can be influenced by different treatment techniques (e.g. hydrogen passivation)  currently under investigation

10/16 Nawrodt, Genoa 09/2009 Monolithic Waveguide Mirror [Li et al., Appli. Phys. Lett. 83 (2003)] Brownian thermal noise estimate  = 0.5 pm S/V = 4/t (t … thickness) µ ~ 3 for very small structures the size dependence of the Young’s modulus needs to be considered no additional losses are assumed (TE cancelled at 18 K)

11/16 Nawrodt, Genoa 09/2009 Monolithic Waveguide Mirror Brownian thermal noise estimate monolithic waveguides have a smaller contribution than the bulk thermal noise modelling still at an early stage total thermal noise, 18 K18 K

12/16 Nawrodt, Genoa 09/2009 Suspension thermal noise The mechanical loss of silicon suspension elements arises from 3 main contributions – thermoelastic, surface and intrinsic bulk. Thermoelastic peak shifts to higher frequencies while cooling. 300 K 50 K  680 µm

13/16 Nawrodt, Genoa 09/2009 Suspension thermal noise 18 K simple TN estimate for 1 stage monolithic suspension full treatment (with correlations) leads to higher thermal noise in the pendulum noise (see e.g. poster P. Amaldi8) circular Si(100) fibre (  680 µm, 4 fibres for each optical element, L = 1 m) mirror (180 kg,  500 mm, Si(111)) beam radius 90 mm

14/16 Nawrodt, Genoa 09/2009 Experimental work mechanical loss of coating materials (understanding and reduction of mechanical loss) mechanical loss of silicon flexures (extraction of surface loss, influence of surface treatment) silicon bonding, mechanical loss of bonds (bond loss values needed for realistic design) strengths of bonds (300 and 80 K) (pieces need to be bonded, mechanical “stability”)

15/16 Nawrodt, Genoa 09/2009 Bond experiments bond technique needs to be characterised for the design: mechanical properties (breaking strength, mechanical loss, Young’s modulus) thermal properties (thermal conductivity, collaboration with the Florence group) details at the ET annual meeting

16/16 Nawrodt, Genoa 09/2009 Future work refined suspension model based on realistic design information needed on exact design, temperature distribution, requirements due to cooling strategy Xylophone “option” (optimisation, noise levels) heat extraction concepts combination of results  suggestions for design study

17/16 Nawrodt, Genoa 09/2009 coating limit is valid for all our design curves!

18/16 Nawrodt, Genoa 09/2009 number  T/Kgeometryoscillatorreference 11.5× µ m × 4 … 6 µ m × 60 nm cantileverStowe1997 [5] 24.0× … 300 µ m × 10 µ m × 70 nm cantileverYasamura2000 [6] 31.2× µ m × 3.9 µ m × 290 nm cantileverMamin2001 [7] 45.0× µ m × 45 µ m × 1.5 µ m cantileverWago1995 [8] 55.0× KNT geometry 50 µ m cantilever Glasgow/Jena2009 (unpublished) [9] 64.4× mm × 10 mm × 92 µ m cantileverReid2006 [10] 73.0× mm × 8 mm × 130 µ m cantileverKroker2009 diploma [11] 81.0× µ m DPOMihailovich1992 [12] 92.2× µ m DPOSpiel2000 [13] 105.0× µ m DPOKleiman1987 [14] 111.3×  10 cm × 0.5 mm diskZendri2008 [15] 122.2×  7.6 cm × 1.2 cm cylinderNawrodt2008 [16] 135.0×  10.6 cm × 22.9 cm cylinderMcGuigan1978 [17] Reference list of the surface loss extraction data

19/16 Nawrodt, Genoa 09/2009 [5]T. D. Stowe et al., Attonewton force detection using ultrathin silicon cantilevers, Appl. Phys. Lett. 71 (1997) 288. [6]K. Y. Yasamura et al., Quality Factors in Micron- and Submicron-Thick Cantilevers, Journal of Microelectromechanical Systems 9 (2000) 117. [7]H. J. Mamin, D. Rugar, Sub-attonewton force detection at millikelvin temperatures, Appl. Phys. Lett. 79 (2001) [8]K. Wago et al., Low-temperature magnetic resonance force detection, J. Vac. Sci. Technol. B 14 (1996) [9]unpublished (measurements in June/July 2009) [10]S. Reid et al., Mechanical dissipation in silicon flexures, Phys. Lett. A 351 (2006) 205. [11]S. Kroker, diploma thesis, University of Jena, [12]R. E. Mihailovich, J. M. Parpia, Low Temperature Mechanical Properties of Boron-Doped Silicon, Phys. Rev. Lett. 68 (1992) [13]C. L. Spiel, R. O. Pohl, Normal modes of a Si(100) double-paddle oscillator, Rev. Sci. Instrum. 72 (2001) [14]R. N. Kleiman et al., Two-Level Systems Observed in the Mechanical Properties of Single-Crystal Silicon at Low Temperatures, Phys. Rev. Lett. 59 (1987) [15]J. P. Zendri et al., Loss budget of a setup for measuring mechanical dissipations of silicon wafers between 300 and 4 K, Rev. Sci. Instrum. 79 (2008) [16]R. Nawrodt et al., High mechanical Q-factor measurements on silicon bulk samples, J. Phys.: Conf. Ser. 122 (2008) [17]D. F. McGuigan et al., Measurements of the Mechanical Q of Single-Crystal Silicon at Low Temperatures, J. Low. Temp. Phys. 30 (1978) 621.