1Alban REMILLIEUX 3rd ILIAS-GW Annual General Meeting. London, October 26th-27th, 2006

New coatings on new substrates for low mechanical loss mirrors

1. Mechanical loss measurement bench 2. New high index coating materials

3. New substrates

Task M4

2Alban REMILLIEUX 3rd ILIAS-GW Annual General Meeting. London, October 26th-27th, 2006

New coatings on new substrates for low mechanical loss mirrors

• Mirror thermal noise is predicted to be the limiting noise in the most sensitive band around 100 Hz• Much of this thermal noise comes from the optical coatings of the interferometer mirrors• The thermal noise is caused by mechanical loss in the system

1 10 100 1000 1000010-23

10-22

10-21

10-20

10-19

10-18

(a) Virgo Nominal sensitivity (b) Seismic noise (c) Pendulum thermal noise (d) Mirror thermal noise (e) Shot Noise

h(f) [1/

sqrt(H

z)]

Frequency [Hz]

(a)

(b)

(c)

(d)

(e)

3Alban REMILLIEUX 3rd ILIAS-GW Annual General Meeting. London, October 26th-27th, 2006

1. Mechanical loss measurement bench

• 3 years ago, no metrology at LYON, R&D on low mechanical coatings was very slow • Delivery of the bench in April 2004 thanks to a collaboration with INFN Perugia• Quick and low cost measurement for the search of new coatings at LMA• Measurement at low frequency around 100 Hz

• Freely decaying resonant motion of the membrane • HeNe laser reflected by the membrane

4Alban REMILLIEUX 3rd ILIAS-GW Annual General Meeting. London, October 26th-27th, 2006

: mechanical loss

: resonant frequency

1. Mechanical loss measurement bench

5Alban REMILLIEUX 3rd ILIAS-GW Annual General Meeting. London, October 26th-27th, 2006

1. Mechanical loss measurement bench

with

Thin membranes of silica (Suprasil 311)45 mm x 5 mm x 110 µm

6Alban REMILLIEUX 3rd ILIAS-GW Annual General Meeting. London, October 26th-27th, 2006

2. New high index coating materials

First generation Virgo mirrors (stack of SiO2 / Ta2O5):

4

4

100.3

105.0

52

2

OTa

SiO

• The high index material is highly responsible for the mirror mechanical losses

• Search for a new low mechanical loss, high index coating material

7Alban REMILLIEUX 3rd ILIAS-GW Annual General Meeting. London, October 26th-27th, 2006

Coating material Absorption (ppm) Mechanical losses

Ta2O5 0.5

Ta2O5 : W 2.45

Ta2O5 : W+Ti 1.65

Ta2O5 : Co 5 000 !

ZrO2 11

ZrO2 : Ti 37

ZrO2 : W 10

4: 102.352

TiWOTa

3: 101.152 CoOTa

It is not easy to lower the mechanical loss without increasing the absorption

A low stressed coating is not necessarely a low mechanical loss coating

2. New high index coating materials

4: 105.752 WOTa

4: 108.22

WZrO

4: 108.62

TiZrO

4103.22

ZrO

Before annealing

4100.352

OTa

Thickness is 500 nm

8Alban REMILLIEUX 3rd ILIAS-GW Annual General Meeting. London, October 26th-27th, 2006

2. New high index coating materials

Our best high index coating material :

4100.352

OTa

4*: 102.2

52

TiOTa

4: 104.252

TiOTa

Advanced LIGO requirement :

Advanced LIGO goal :

Optimization of the Ti concentration

Mirrors SiO2/Ta2O5:Ti ** on 3 inch diameter substrates sent to LIGO for mechanical loss measurement

Mirrors SiO2/Ta2O5:Ti ** (standard and optimized) on membranes for LMA mechanical loss measurement

Search for other binary oxydes, ternary compounds

4100.1 indexHigh

4105.0 indexHigh

With Ta2o5 : Ti

Absorption is unchanged : 0.5 ppm

Refractive index is high : 2.1

9Alban REMILLIEUX 3rd ILIAS-GW Annual General Meeting. London, October 26th-27th, 2006

3. New substrates

• silicon membranes from Glasgow

• 500 nm Ta2O5:Ti « formula 5 » coating

• Good adhesion if membrane previously annealed

10Alban REMILLIEUX 3rd ILIAS-GW Annual General Meeting. London, October 26th-27th, 2006

• Mechanical loss measurements made at LMA

• To be compared with Glasgow measurements

3. New substrates

Mode # 1 2 3

Resonant frequency (Hz) 29.65 183.14 511.56

1.1 10-4 1.5 10-4 1.4 10-4

68 mm x 10 mm x 100 µm Si membrane

TiOTa :52

11Alban REMILLIEUX 3rd ILIAS-GW Annual General Meeting. London, October 26th-27th, 2006

• 3" diameter 1“ thick  silicon substrate

• (HB)15 deposited on it after annealing

• H: Ta2O5:Ti « formula 5 »

• B: SiO2

• Good adhesion of the mirror

3. New substrates

12Alban REMILLIEUX 3rd ILIAS-GW Annual General Meeting. London, October 26th-27th, 2006

3. New substrates

• 3" diameter 1.7 mm thick  silica substrate

• etched diffraction grating

• (HB)15 deposited on it

• H: Ta2O5:Ti « formula 5 »

• B: SiO2

• Good adhesion of the mirror

• not measurable because of chipping

• coating will be made again soon

13Alban REMILLIEUX 3rd ILIAS-GW Annual General Meeting. London, October 26th-27th, 2006

• LMA has developed new high index coating materials, enabling a  reduction of the mechanical losses by a factor of 1.5 with good optical performances.

• The research for new coating materials has been made easier thanks to a mechanical loss measurement bench developed in the laboratory. This research is still going on with Advanced Virgo and Advanced LIGO R&D.

• Coatings have been successfully deposited on a new substrate, silicon, which has interesting properties at low temperature.

• A silica substrate, with an etched diffraction grating on it, has also been coated with a low mechanical loss mirror.

Conclusion