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Janyce Franc, Nazario Morgado, Raffaele Flaminio Laboratoire des Matériaux Avancés CNRS Villeurbanne, FRANCE Tuesday 18th May 2010. Simulation and research for the future ET mirrors. Contents. Mirror Thermal Noises Solutions to reduce Mirror Thermal Noise Find New materials

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Simulation and research for the future ET mirrors


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slide1
Janyce Franc, Nazario Morgado, Raffaele Flaminio

Laboratoire des Matériaux Avancés

CNRS

Villeurbanne, FRANCE

Tuesday 18th May 2010

Simulation and research for the future ET mirrors

Janyce Franc-Kyoto-GWADW

contents
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

Janyce Franc-Kyoto-GWADW

slide3

Mirror thermal noises and ET

Adv. Virgo

ET

w=6 cm

Infinite mirror

Unless otherwise specified

Janyce Franc-Kyoto-GWADW

slide4

Coating Brownian noise

Reduce the temperature

Reduce losses by new coating materials

Change the beam shape and size

Increase the Ysub by changing the material substrate

Janyce Franc-Kyoto-GWADW

slide5

Coating materials

N.B. Parameters available in J.Franc et al. ET-02109

Janyce Franc-Kyoto-GWADW

slide6

Coating materials

Comparison of different coatings

with same transmission (6 ppm)

SiO2-Ti:Ta2O5 coating offers the best result

SiO2-Nb2O5 is also a good candidate (but absorption slightly higher)

N.B. Parameters available in J.Franc et al. ET-02109

Janyce Franc-Kyoto-GWADW

slide7

Substrate materials (300K)

TE Noise limits the Si and Sapphire TN

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)

Janyce Franc-Kyoto-GWADW

slide8

Low temperature: substrate materials

10K

SiO2 is unsuitable

Similar level for Silicon and Sapphire.

Silicon is promising because of its interest in microelectronics industry.

Janyce Franc-Kyoto-GWADW

slide9

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)

Janyce Franc-Kyoto-GWADW

slide10

Low temperature: Silicon

Large sensitivity variation vs Temperature!

Good results obtained at 4-20K

30K must be avoided

No real interest in working at 18 K because of

Substrate Brownian noise

Coating losses (see next slide)

Janyce Franc-Kyoto-GWADW

slide11

Low temperature: Coating losses

18K

10K

I. Martin et al. Class. Quantum Grav. 25 (2008) 055005

Janyce Franc-Kyoto-GWADW

slide12

Beam shape (and size)

To reduce Thermal noise the beam shape and size can be changed.

  • Advantages :
  • -Best power distribution on the mirror surface
  • Lower Thermal Noise
  • Lower Thermal Lensing

Janyce Franc-Kyoto-GWADW

slide13

Beam shape: thermal noise reduction

LG55 does not demonstrate better results

ET NOTE with all the results: soon available

Janyce Franc-Kyoto-GWADW

slide14

Solutions for ET

Reference : S. Hild et al., CQG, 2010, 27, 015003

Janyce Franc-Kyoto-GWADW

slide15

Solutions for ET

At low frequency : 45 cm diameter + silicon + 10K+ TEM00 is enough

At higher frequency : 62 cm diameter + silica + 300K+ LG33 is possible

Janyce Franc-Kyoto-GWADW

slide16

Study of coating losses at LMA

Coating deposit chambers at LMA

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.

* Ta2O5

* Ti:Ta2O5

* SiO2

Mechanical losses measurement at LMA

Janyce Franc-Kyoto-GWADW

slide17

Q of silica layers

Cantilever welded to Silica block

Silica block

Silica cantilever

Collaboration INFN Perugia (H. Vocca)

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.

Janyce Franc-Kyoto-GWADW

slide18

Q of high index materials

Measurements generally done for a 500 nm thick film.

BUT some variation observed when different thickness are measured…

Preliminary studies – Need more measurement before to conclude!

Janyce Franc-Kyoto-GWADW

slide19

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

Some preliminary results :

Janyce Franc-Kyoto-GWADW

slide20

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 losses

evaluate silicon optical properties

develop LG interferometry

…….

- Study of coating losses at LMA with cantilevers:

Confirm low losses for silica mono layers

Shows some excess of losses in thick coatings to be better investigated

Janyce Franc-Kyoto-GWADW

slide21

Solutions for ET

At low frequency : 45 cm diameter + silicon + 10K+ TEM00 is enough

At higher frequency : 62 cm diameter + silica + 300K+ LG33 is possible

Janyce Franc-Kyoto-GWADW

slide22

Low temperature: other coating noises?

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!

- b= 25 10-4 K-1

200 times larger than at 300 K!

Unlikely

=6 10-5 (K-1)

Thermal Exp. coefficient limits sensitivity if value 20 times larger than value @ 300 K

Janyce Franc-Kyoto-GWADW