Geppo Cagnoli INFN Sez. Firenze University of Glasgow ESF Workshop – 22 nd Sep. 2005, Perugia

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


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


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…


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


Flames at work


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


CO2 laser at work


Machine conceptual design

• Able to pull:– Circular fibres– Ribbons

• Able to weld

• Modular design

3 axesmachine


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


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


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


Some pictures


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


Ear strength tests

Breaking load: 9.5 kgFlame polished

37.5 kg breakingload

12 kg loadOn since19/08


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


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

Geppo Cagnoli INFN Sez. Firenze University of Glasgow ESF Workshop – 22 nd Sep. 2005, Perugia

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