Development of Fused S ilica S uspension Fibres for Advanced - - PowerPoint PPT Presentation

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Development of Fused S ilica S uspension Fibres for Advanced Gravitational Wave Detectors TAUP S endai 11 th S eptember 2007 Alastair Heptonstall Institute for Gravitational Research University of Glasgow Hept onst all, Bart on, Cagnoli,

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Hept onst all, Bart on, Cagnoli, Cumming, Faller, Hough, Jones, Mart in, Rowan, S t rain, Veggel, Zech

Development of Fused S ilica S uspension Fibres for Advanced Gravitational Wave Detectors

TAUP S endai 11th S

eptember 2007

Alastair Heptonstall

Institute for Gravitational Research University of Glasgow

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Hept onst all, Bart on, Cagnoli, Cumming, Faller, Hough, Jones, Mart in, Rowan, S t rain, Veggel, Zech

Monolithic suspensions for advanced detectors

  • Development of monolithic suspensions

is based on experience from the GEO600 suspensions

  • This talk will cover aspects of

production and testing of suspension elements suitable for Adv. LIGO and upgrades to Virgo

  • The criteria that must be met by ribbon

fibres for Adv. LIGO:

S

trength (x3 safety margin)

Thermal noise performance

  • To meet these criteria we require

Breaking stress > 2.4 GPa Intrinsic loss <3 x 10-11/ t, where t is

the thickness of the ribbon

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Hept onst all, Bart on, Cagnoli, Cumming, Faller, Hough, Jones, Mart in, Rowan, S t rain, Veggel, Zech

Improving fibre pulling technology

  • Advanced LIGO suspensions require ±1.9%

tolerance on fibre dimensions.

  • This is a slight increase on the ±2.1%

achieved in GEO600.

  • Repeatability and tolerance in flame

pulling machines is limited by gas regulation and slack in mechanical parts.

  • A new machine was developed in

Glasgow using a CO2 laser and high precision drive systems

  • Designed for both ribbon and cylindrical

fibre production to be suitable for both LIGO and Virgo upgrades.

  • The machine is also capable of welding

fibres.

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Hept onst all, Bart on, Cagnoli, Cumming, Faller, Hough, Jones, Mart in, Rowan, S t rain, Veggel, Zech

Pulling fibres using the CO2 laser

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Hept onst all, Bart on, Cagnoli, Cumming, Faller, Hough, Jones, Mart in, Rowan, S t rain, Veggel, Zech

Virgo laser pulling machine installation

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Hept onst all, Bart on, Cagnoli, Cumming, Faller, Hough, Jones, Mart in, Rowan, S t rain, Veggel, Zech

Diameter of CO2 pulled fibre in region of taper

500 1000 1500 2000 1 2 3 4 5 6 7 8 9 10 Travel /mm Diameter (micron)

1 2 3 4 5 Length (mm) Diameter (µm) 1000 1500 2000 500

Controlled shaping of the neck

1 2 3 4 Length (mm) 200 600 1000 1400 Diameter (µm)

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Hept onst all, Bart on, Cagnoli, Cumming, Faller, Hough, Jones, Mart in, Rowan, S t rain, Veggel, Zech

Mechanical loss in CO2 laser pulled fibres

0.E+00 2.E-07 4.E-07 6.E-07 8.E-07 1.E-06 1 10 100 1000 10000 Frequency (Hz) Loss

0.E+00 2.E-07 4.E-07 6.E-07 8.E-07 1.E-06 1 10 100 1000 10000 Frequency (Hz) Loss

m 10 05 . 6

12 −

× =

surface

hφ

  • Four S

uprasil 300 fibres of diameter ~470µm were measured

  • Initial analysis of losses shows a surface loss consistent with:
  • S

uprasil 300 is not necessarily expect ed to be similar to 312 or 311 as it has a different manufacturing process and a lower OH content

  • From Penn et al we can calculate values:

m 10 3.25

  • 12

× =

surface

hφ m 10 7 . 4

12 −

× =

surface

hφ

for suprasil 312 for suprasil 2

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Hept onst all, Bart on, Cagnoli, Cumming, Faller, Hough, Jones, Mart in, Rowan, S t rain, Veggel, Zech

Where does dissipation arise in our material?

  • In order to reduce thermal noise we need to reduce

dissipation.

  • To do this we must first understand where it arises.
  • Loss in fused silica is normally split into two categories
  • Bulk

A very low level dissipation in the body of the material recently shown to be due to the residual effects of dissipation due to a two level system

  • S

urface A much higher level of dissipation in the damaged surface layer

  • The dominant loss mechanism depends on surface to volume

ratio.

  • This can now be controlled to a level acceptable for next

generation detectors

  • However a better understanding of the physics of these loss

mechanisms is needed to reduce thermal noise for future detectors

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Hept onst all, Bart on, Cagnoli, Cumming, Faller, Hough, Jones, Mart in, Rowan, S t rain, Veggel, Zech

Recent measurements at Glasgow (1)

0.0E+00 5.0E-08 1.0E-07 1.5E-07 2.0E-07 2.5E-07 3.0E-07 3.5E-07 0.05 0.1 0.15 1/ Length Measured loss minus thermoelastic

  • Loss measurements made on laser

pulled fused silica fibres have shown a length dependence to dissipation

  • This is consistent with a source of

loss close to the top of the fibre

  • This has been shown analytically and

using finite element modelling

  • S
  • urce of loss thought to be due to

welding

  • This is a previously unknown source
  • f loss – highly relevant for

development of detector suspensions

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SLIDE 10

Hept onst all, Bart on, Cagnoli, Cumming, Faller, Hough, Jones, Mart in, Rowan, S t rain, Veggel, Zech

Recent measurements at Glasgow (2)

0.E+00 2.E-07 4.E-07 6.E-07 8.E-07 1.E-06 0.02 0.04 0.06 0.08 0.1 0.12 1/ length residual loss

470um welded directly on fibre 470um welded directly on fibre 470um welded directly on fibre 345um welded with a few mm above the neck

welded with a neck

  • Each weld gives different

value for loss

  • When viewed under a

microscope possible loss mechanisms can be seen

  • Fibre attached using thick

neck shows lowest loss as less energy stored in weld

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SLIDE 11

Hept onst all, Bart on, Cagnoli, Cumming, Faller, Hough, Jones, Mart in, Rowan, S t rain, Veggel, Zech

Recent measurements at Glasgow (3)

1.00E-07 1.20E-07 1.40E-07 1.60E-07 1.80E-07 2.00E-07 2.20E-07 2.40E-07 500 1000 1500 2000 2500 3000 3500 4000 Frequency (Hz) Measured loss minus thermoelastic

  • Analysis of dissipation in fibres has shown evidence of a

frequency dependent bulk loss seen at a higher than expected level

  • Approximately 10 times that seen in bulk samples
  • At higher frequencies this contributes as much as 25%
  • f loss
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Hept onst all, Bart on, Cagnoli, Cumming, Faller, Hough, Jones, Mart in, Rowan, S t rain, Veggel, Zech

Ribbon fibre development

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Hept onst all, Bart on, Cagnoli, Cumming, Faller, Hough, Jones, Mart in, Rowan, S t rain, Veggel, Zech

Ribbon cross-sectional shape development

  • First ribbon fibres pulled had a non-

rectangular cross-section due to heat loss from edges.

  • Laser was run at close to maximum power

due to heat loss.

  • Polished aluminium heat shield was

developed to reflect heat back at edges.

  • Further improvements to the symmetry of the

fibre neck and cross section were achieved by using slides on either side to reduce the edge effects.

  • Laser stabilisation has been significantly

improved

Fast sensor Wedged Brewster window for pick-off

  • Profile of pull has been investigated to create

good shapes for the neck regions Initial cross-section Using heat shield Using heat shield & side slides

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Hept onst all, Bart on, Cagnoli, Cumming, Faller, Hough, Jones, Mart in, Rowan, S t rain, Veggel, Zech

Profiling of ribbon dimensions

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Hept onst all, Bart on, Cagnoli, Cumming, Faller, Hough, Jones, Mart in, Rowan, S t rain, Veggel, Zech

S trength and bounce frequency testing

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Hept onst all, Bart on, Cagnoli, Cumming, Faller, Hough, Jones, Mart in, Rowan, S t rain, Veggel, Zech

Welding technology

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Hept onst all, Bart on, Cagnoli, Cumming, Faller, Hough, Jones, Mart in, Rowan, S t rain, Veggel, Zech

Bonding test mass ears at LAS TI (1)

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Hept onst all, Bart on, Cagnoli, Cumming, Faller, Hough, Jones, Mart in, Rowan, S t rain, Veggel, Zech

Bonding test mass ears at LAS TI (2)

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Hept onst all, Bart on, Cagnoli, Cumming, Faller, Hough, Jones, Mart in, Rowan, S t rain, Veggel, Zech

Conclusions

  • Based on the experience of the flame pulling machines used for the GEO600 suspensions

we have designed and built new fibre pulling machines using CO2 lasers

  • Laser pulled cylindrical fibres have a surface loss at a similar level to flame pulled fibres
  • Data shows evidence of length dependent loss which appears to be related to the quality
  • f weld
  • There is strong evidence of frequency dependence in residual loss of fibres st udied
  • This appears to arise due t o dissipation in the bulk of the fibre material but at a higher

level of loss than is seen for larger ‘ bulk’ samples

  • Both the above effects need included in any model of suspension thermal noise in

monolithic silica suspensions

  • Further studies in progress
  • The construction of the monolithic pendulum stage for LAS

TI has begun, with successful bonding of the ears to both the penultimate and test masses