Overview on thermal noise reduction research for future GW detectors. G. Cagnoli, LMA

Transcription

1 Overview on thermal noise reduction research for future GW detectors G. Cagnoli, LMA GWADW 2014 Takayama

2 Sensitivity limits in Advanced Detectors Suspensions: Silica fibres Length <1m Thermoelastic cancellation Vertical mode frequency <10 Hz Substrates and Coatings: Silica substrates Optimal aspect ratio Ti:Ta2O5/SiO2 coatings Optimal coating design 2

3 Sensitivity curves beyond the Advanced detectors Nic Smith s talk RED 3 Kazuiro Yamamoto s talk a 3

4 Comparison of thermal noise levels 1E 18 Suspensions 1E 19 1E 20 aligo ET-HF ET-LF 1E 21 1E 22 How do we go from Advanced to Future detectors? 4

5 Suspension Thermal Noise In the detection bandwidth, interferometers work above the pendulum resonant frequency Log [S xx ] S xx T 1 m f 5 g L Dil ϕ fibre Dil = For fibres with a neck the dilution is almost independent on mass 2 r L π Y m g Log f Fixing the fibres radius Thermo-elastic cancellation in silica (~190Mpa) Sufficient heat conduction for sapphire and Si Dil in ET-LF = 2.6 x Dil in aligo Cumming 2009 Summing them up: 1/30 from T 1/5 from m 1/3 from L 1/10 from ϕ S xx may decrease 67 times 5

6 Comparison of thermal noise levels 1E 18 Suspensions 1E 19 1E 20 aligo ET-HF ET-LF 1E 21 1E times reduction What scientific and technological advancements are needed to secure the result? 6

7 Two concepts for warm suspensions Cumming 2012 Advanced Virgo Courtesy of H. Vocca, Perugia 7

8 Technologies for warm suspensions Fused silica fibres Heavier masses require thicker fibres Breaking strength is related to the probability to have a flaw in the fibre, which is proportional to the volume Tapering A sharp neck increases the dilution factor Bonding Shear or compressive stress Bonding silica to silica coated steel Cantilever blades DLC protective coating increases handling Ross Birney s talk Courtesy of H. Vocca, Perugia 8

9 Technologies for cold Crystalline fibres µpulling Vertical growth Machining suspensions - 1 Bonding New challenges come from: M. Van Veggel s talk and poster 1) the cryogenic environment Thermal cycling 2) Sapphire and silicon bonding 3) Indium bonding? Alshourbagy 2009 S. Rowan s talk, GWADW

10 Technologies for cold suspensions - 2 Crystalline LF vertical suspensions Cantilevers Elements under compression Eric Hennes s posters F A. Cumming s talk, 5 th ET Symposium G. Hammond s poster on breaking stress of sapphire E. Majorana s talk, GWADW 2013 Cradles Raul Kumar s talk 10

11 Scientific investigations Thermal noise under heat currents Giles Hammond s poster on Johnson noise Livia Conti s talk Daniel Heinert s poster on non-eq. Th.Ns. Surface relaxations in mechanical losses of amorphous and crystalline materials Dmitry Koptov s poster on the ESD effect on test masses Zach Korth s poster on silicon ribbons noise Can we have a factor 10 gain over fused silica losses? Nic Smith s poster on continous measurement of Q 11

12 Mirror thermal noise Log [S xx ] Log f Mirror noises are always below resonance: little gain from substrate Young s modulus Y Sapphire ~ 2.9 x Y Silicon ~ 2.2 x Y Silica Granata 2013 Substrate Brownian Substrate thermo-elastic S xx T 2 S xx T 2 α κ (C ρ) w f 2 1 Y w 1 w f ϕ S Coating Brownian S xx 1 d T Y w f 2 ϕ C DOMINANT TERM SO FAR S xx T 2 C s 1 ρ κ s w 2 1 f αc d α d s C C c s ρc ρ s β C λ 2 Coating thermo-optic 12

13 Playing with numbers 1/30 from T 1/1.7 2 from w 1/x from ϕ 1E 18 1E 19 Coating loss reduction of 2.7 times aligo S xx x x may decrease: 300 K 10 K The 1.7 factor may increase further if the LG33 mode replaces the TEM00 in the cavities 1E 20 1E 21 1E ET-HF ET-LF Alberto Gatto s talk 13

14 The factor x in the Amorphous Coatings Room temperature: Doping of Ta2O5 with Ti developed at LMA Heat treatment Effects at low T At room T Martin 2010 Massimo Granata s talk New materials and new doping Steve Penn s research on Zr02 Nano-structured layers 3e-4 ϕ TA2O5 2e-4 1.6e-4 14e-4 Harry TiO2 concentration Granata 2013 Innocenzo Pinto s talk Low temperature. ϕ coat (10K) is ~2 x ϕ coat (300K) 10e-4 ϕ stack 4e T [K] 14

15 Structural studies To understand which are the relaxations responsible of thermal noise in amorphous materials The intelligent design of coatings follows Strategy LIGO-Virgo meeting August 29 th -Stanford 6 th ET Symposium November 20 th -Lyon Riccardo Bassiri s talk Multi-technique analysis of static structure (x-rays and electronic diffraction) or dynamic (Raman) M. Granata s talk Correlation studies with mean properties like mechanical losses or Anghinolfi JPD 2013 refractive index Molecular dynamics models Controlled alteration of coatings 15

16 Crystalline coatings Low temperature operation AlGaP grown on Si AlGaAsgrown on GaAs and lift off onto substrates Iain Martin s talk Room temperature operation Lift off technique Thermo-optic noise seems under control Optical properties 5 to 13ppm absorp. measured on Cole s coatings Point like defects are sometimes present Scattering measurements A. Lin s talk, GWADW

17 Crystalline substrates Silicon CZ vs FZ Homogeneity of impurities and of thermo-optical and mechanical parameters Effect of crystalline axis orientation Sapphire Absorption Gerd Hofmann s talk R. Nawrodt s talk, GWADW

18 Advancements in optics LG33 Alberto Gatto s talk Results from the latests experiments Folded FP cavities Stefan Balmer s talk The history kicks back! Sampling ideally the whole mirror surface Centre of Mass detection 18

19 Parameters for different generations 300 K 20 K 300 K 10 K 300 K 10 K 300 K 10 K 300 K 10 K 300 K 10 K 19

20 Conclusion Progresses are constants There are good chances to reach the expected noise levels for future detectors A POSITIVE COMPETITION BETWEEN MATERIAL RESEARCH AND OPTICS IS NECESSARY 20