Low noise Fused Silica suspensions: from the GEO600 experience to the 2 nd generation requirements Geppo Cagnoli INFN Sez. Firenze University of Glasgow ESF Workshop – 22 nd Sep. 2005, Perugia
Jan 05, 2016
Low noise Fused Silica suspensions: from the GEO600
experience to the 2nd generation requirements
Geppo CagnoliINFN Sez. Firenze
University of Glasgow
ESF Workshop – 22nd Sep. 2005, Perugia
22nd Sep. 2005 ESF Workshop - Perugia 05 - Silica suspensions 2 of 17
Fundamental milestones
• Braginsky, Mitrofanov, Tokmakov
1990 2000 201095 9796
• Silica cradle (Glasgow)
• Silicate bonding, J. Gwo
98 99 01 02
• Bi-filar pendulum,Moscow-Glasgow
• Bi-filar pendulum,Glasgow-Perugia
• First flame pullingmachine in Glasgow
• 1st silica suspensions in GEO600
03
• 2nd silica suspensions in GEO600
04
• EGO R&D onCO2 laser machine
• Advanced LIGO
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Pro and Cons of Silica
• Thermal noise– Low mech. losses– Low Young’s
modulus– Monolithic
suspensions
• Other issues– Tapering– Low excess noise
(bursts ?)
• Safety– Careful handling– Ears breaking
• Cleanness– Welding on situ
• Electrical– Charging of test
masses
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Something we have learned
• Broken fibres can be replaced• Teflon can be applied on the fibres• The reproducibility of fibres was not
optimal• The flame blows the fibre during
welding• Manual welding is dirty and not
reproducible• Probably side welding better than
bottom welding (work in progress)• After all the fibres are still there…
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Limitation of the H2-O2 technology in GEO600
– Metal nozzles•Surface contamination by combustion
products can limit strength– Shape control - limited
• Very approximate with pulling machines• More accurate with feed & pull
– Reproducibility - limited• Uniformity of cross sectional area at ~
10% level in GEO 600
– Welding• Contamination with combustion products• Blowing of the flame
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Flames at work
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The new technology: CO2 laser
• Use CO2 laser radiation (10.6 m) to melt silica
• Potential advantages of laser fabrication & weld:– Very fine control of quantity and
localization of heating– Reduced contamination– Diameter self-regulation effect– Precision welding – improved weld shape– Welding of thin fibres on thick rods– No blowing
• Full control on beam delivering– Re-correction of shape, stress relief/annealing
afterwards
10.6 m
McLachlan & Meyer, Applied Optics Vol 26 No. 9, 1987
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CO2 laser at work
22nd Sep. 2005 ESF Workshop - Perugia 05 - Silica suspensions 9 of 17
Machine conceptual design
• Able to pull:– Circular fibres– Ribbons
• Able to weld
• Modular design
3 axesmachine
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Conceptual design for cylindrical fibres
• Current conceptual design of cylindrical fibre machine
– fibre stock clamped to base of machine
– focus of laser (ring) moved downwards to progressively melt stock
– upper stock clamp moves upwards to draw fibre
CO2 laser beam 10.6m
Silica fibre
Conical mirror
Rotating45° mirror
Motor
PULL
FEED
Silica rod
Block C
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Conceptual design for ribbons and welding
• Block C is here an XY scanner (mirror galvanometers) mounted on a rotational stage
• A3 and the rotational stage are used for welding
• The laser path is the b one
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Some results
0
100
200
300
400
500
600
0 10 20 30 40 50 60
Distance down fibre (mm)
Dim
ensi
on
(m
)
1 mm stock
2 mm stock
0
50
100
150
200
250
300
0 20 40 60 80 100 120 140
Distance along Fibre (mm)
Fib
re D
iam
eter (
mic
ron
s)
Hand Pull 1 Hand Pull 2 Motorised pull 1 Motorised Pull 2
0
100
200
300
400
500
600
700
800
900
0 50 100 150 200 250 300 350 400 450 500 550
Distance along fibre (mm)
Dia
mete
r (m
icro
ns)
Motorised Pull 3 (~580mm fibre) Motorised Pull 3 (same fibre rotated by ~90degrees)
Fibre profile
The neck problemFirst ribbonwith the newmachine
The new3 axespulling
machine
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Some pictures
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The ears for Advanced LIGO
New ears design for the 40 kg
masses of Advanced LIGO
9 cm2 is themaximumbonding surface.Triangular shapefor peeling reduction
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Ear strength tests
Breaking load: 9.5 kgFlame polished
37.5 kg breakingload
12 kg loadOn since19/08
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Suspension thermal noise in Advanced LIGO
1.E-23
1.E-22
1.E-21
1.E-20
1.E-19
1.E-18
1.E-17
1.E-16
1.E-15
1.E-14
1.E-13
1.E+00 1.E+01 1.E+02 1.E+03
Frequency [Hz]
Dis
pla
ce
me
nt
no
ise
[m
/sq
rt(H
z)]
Suspension fibres404um diameter
Suspension fibres800um diameter
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Conclusions
• How much is the confidence in the low frequency performance of the Advanced Detectors?
• The effect of metal suspensions on the internal thermal noise of mirrors is not clear
• The CO2 laser machine seems to be able to produce fibres with the advanced detectors requirements
• The silicate bonded ears are giving a positive response to the test