janyce franc-kyoto-gwadw1 simulation and research for the future et mirrors janyce franc, nazario...
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Janyce Franc-Kyoto-GWADW 1
Simulation and research for the future ET mirrors
Janyce Franc, Nazario Morgado, Raffaele Flaminio
Laboratoire des Matériaux Avancés
CNRS
Villeurbanne, FRANCE
Tuesday 18th May 2010
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Contents
• Mirror Thermal Noises
• Solutions to reduce Mirror Thermal Noise
– Find New materials– Cool down mirrors– Use Laguerre-Gauss modes
• Mirrors for ET
• Coating research activities at LMA
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Mirror thermal noises and ET
w=6 cmInfinite mirror
Unless otherwise specified
ET
Adv. Virgo
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Coating Brownian noise
Reduce losses by new coating materialsReduce the temperature
Increase the Ysub by changing the material substrate
Change the beam shape and size
wfY
TkS
s
scbc
23
2 )1(2
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Coating materials
TiTa2O5 TiO2 Nb2O5 ZrO2 SiO2 Al2O3
2 10-4 6.3 10-3 4.6 10-4 5.9 10-4 0.5 10-4 2.4 10-4
(kg.m-3) 6425 4230 4590 6000 2200 3700
(W.m-1.K-1) 0.6 0.45 1 1.09 0.5 3.3
C (J. K-1.Kg-1) 269 130 590 26 746 310
(K-1) 3.6 10-6 0.5 10-6 5.8 10-6 10.3 10-6 0.51 10-6 8.4 10-6
(dn/dT) 14 10-6 -1.8 10-4 1.43 10-5 10 10-5 8 10-6 1.3 10-6
Y (GPa) 140 290 80 200 60 210
0.23 0.28 0.2 0.27 0.17 0.22
n 2.06 2.3 2.32 2.15 1.45 1.63
N.B. Parameters available in J.Franc et al. ET-02109
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SiO2-Ti:Ta2O5 coating offers the best resultSiO2-Nb2O5 is also a good candidate (but absorption slightly higher)
Coating materials
N.B. Parameters available in J.Franc et al. ET-02109
Comparison of different coatingswith same transmission (6 ppm)
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Substrate materials (300K)
Silica remains the best substrate materials at 300K
Also better from an optical point of view
And available in large pieces (just need to increase budget)
TE Noise limits the Si and Sapphire TN
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Low temperature: substrate materials
Similar level for Silicon and Sapphire. Silicon is promising because of its interest in microelectronics industry.
SiO2 is unsuitable
10K
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Low temperature: Silicon
* Band-to-band absorption reported in literature (Green et al., 1995)
* The total absorption might be higher due to :
- Impurities- Residual conductivity
At 1550 nm impurities expected to be dominant
* The absorption have to be precisely determined!
* Work in progress at LMA
* NB Only 8’’ diameter silicon wafers with the best optical quality are available so far.
Silicon absorption
M. Green and M. Keevers, Optical properties of intrinsic Silicon @ 300K, Progress in Photovoltaic research and Applications, Vol. 3, 189-
192 (1995)
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Low temperature: Silicon
Large sensitivity variation vs Temperature!Good results obtained at 4-20K30K must be avoidedNo real interest in working at 18 K because of
Substrate Brownian noiseCoating losses (see next slide)
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Low temperature: Coating losses
I. Martin et al. Class. Quantum Grav. 25 (2008) 055005
18K
10K
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Beam shape (and size)
Advantages : -Best power distribution on the mirror surface-Lower Thermal Noise-Lower Thermal Lensing
To reduce Thermal noise the beam shape and size can be changed.
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Beam shape: thermal noise reduction
Coating Brownian Noise
Substrate Brownian Noise
Substrate TE noise(frequency dependent)
TEM00/LG33
Infinite mirror1.7 1.9 1.06-1.8
TEM00/LG33
Finite mirror
(Ø:45cm, h:30 cm)
1.6 1.4 1.08-1.86
LG55 does not demonstrate better resultsET NOTE with all the results: soon available
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Solutions for ET
Low frequency ITF High frequency ITF
Temperature 10K 300K
Mirror size Ø : 45 cm
H : 30 cm
Ø : 62 cm
H : 30 cm
Substrate Silicon Silica
Wavelength 1550 nm 1064 nm
Coating Ti:Ta2O5 & SiO2 Ti:Ta2O5 & SiO2
Phi coat 2.10-4 & 0.5.10-4 2.10-4 & 0.5.10-4
Reference : S. Hild et al., CQG, 2010, 27, 015003
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At low frequency : 45 cm diameter + silicon + 10K+ TEM00 is enoughAt higher frequency : 62 cm diameter + silica + 300K+ LG33 is possible
Solutions for ET
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Study of coating losses at LMA
Mechanical losses measurement at LMA
Coating deposit chambers at LMA
* Ta2O5
* Ti:Ta2O5* SiO2
1. The coating are deposited on silica cantilevers in the same coater used for the Virgo mirrors.
2. The Q of the cantilever is measured before coating deposition (200 000-300 000)=> limitation
3. The Q of the cantilever after deposition is measured and we can deduce the coating loss angle.
4. Good system for Tantala. Not enough sensitivity for silica film.
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Q of silica layers
Welded cantilever (frequency of
vibration in Hz)
1st mode 730 000 (50 Hz)
2nd mode 720 000 (300 Hz)
3rd mode 1 250 000 (800 Hz)
Silica cantilever
Silica blockCantilever welded to Silica block
Silica losses (1st mode)
1st cantilever 4.5 (+/- 1) 10-5
2nd cantilever 4.2 (+/- 1) 10-5
In accordance with the reported values of 5.10-5. Need more tests.The tests with classical cantilever did not permit to measure this value.
Collaboration INFN Perugia (H. Vocca)
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Q of high index materials
Preliminary studies – Need more measurement before to conclude!
Materials Losses angles
Ta2O5 3 10-4
Ti:Ta2O5 2 10-4
Nb2O5 4.6 10-4
Measurements generally done for a 500 nm thick film.
BUT some variation observed when different thickness are measured…
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Q of multilayer coatings
1. Q of multilayer coating can be deduced from losses of materials and coating formula.
2. First measurements showed larger losses in multilayer coatings than foreseen. Thought to be due to defects in the coating coming from poor cantilever surface quality.
3. Recently, mechanical losses of different multilayer coatings with no defects have been measured and confirm larger losses than expected.
4. More studies are needed
Coating Thickness
(nm)
Coating
measured
coating theoretical
doped-tantala deduced
0.817H(1.0736L0.8828H)12 0.0851L
3859 2.5 10-4 1.32 10-4 4.2 10-4
0.87B(HB)20HBB 5222 3.4 10-4 1.34 10-4 5.8 10-4
Some preliminary results :
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Conclusions
- By combining different solutions (larger beams, LG modes, Silicon and low T) the ET sensitivity seems achievable.
- But a strong R&D program is necessary to:reduce coating lossesevaluate silicon optical propertiesdevelop LG interferometry…….
- Study of coating losses at LMA with cantilevers:Confirm low losses for silica mono layersShows some excess of losses in thick coatings to be better investigated
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At low frequency : 45 cm diameter + silicon + 10K+ TEM00 is enoughAt higher frequency : 62 cm diameter + silica + 300K+ LG33 is possible
Solutions for ET
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Low temperature: other coating noises?
=6 10-5 (K-1)
Thermal Exp. coefficient limits sensitivity if value 20 times larger than value @ 300 K
At low temperature a lot of the coating parameters are unknown.
The thermoelastic ( coef.) and thermorefractive ( coef.) noises can not be evaluated.
Question: how large should and to become limited by TE and TR noises?
Answer:- = 6 10-5 K-1
20 times larger than at 300 K! - = 25 10-4 K-1
200 times larger than at 300 K!
Unlikely