High Reflectivity
Mirrors Technology
Laurent PINARD
Technical Manager
Laboratoire des Matériaux Avancés - Lyon
June 24, 2009 - IPNL
POSIPOL 2009
Laurent Pinard
1
OVERVIEW
 Introduction – LMA Presentation
Cavity mirrors Realizations
 Substrates Choice and substrates preparation
 IBS deposition technique
 High reflectivity multilayers
 Optical Performances
Optical Metrology
Preserving performances vs time
June 24, 2009 - IPNL
POSIPOL 2009
Laurent Pinard
2
Introduction – LMA Presentation
Laboratoire des Matériaux Avancés in Lyon
UPS from IN2P3/CNRS (Unité Propre de Service) since 2004 (before IPNL)
Group of 12 engineers, 2 Physicists
Specialized in the study, the realization and the characterization of thin films
realized by various deposition processes (CVD, PVD).
150 m2 clean room class 1 :
Deposition systems, metrology
Cleanliness Importance
Low loss coatings
On small and large
Components for cavities
(Mirrors, AR, dichroic...)
June 24, 2009 - IPNL
POSIPOL 2009
Laurent Pinard
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Introduction - Realizations
 Gyrolaser mirrors : Sagem (since 1990)
 Mirrors on Sapphire substrates : finesse 100 000 at 300°K and 4°K
University of Western Australia (1996)
 Cavity mirrors for Hera DESY (finesse 30 000) : 2001 (V. Brisson)
 Mirrors for the BMV ((Magnetic Birefringence of Vacuum) cavity: C. Rizzo (2007)
Finesse > 500 000
 Project MIGHTYLASER (F. Zomer) : Finesse 30 000 and 300 000
June 24, 2009 - IPNL
POSIPOL 2009
Laurent Pinard
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Introduction - Realizations
 Diameter = 350 mm,
 Thickness = 96 mm, Weight = 20 kg
SIDE B
measurements
VIRGO
specifications
LMA
mesurements
average
scattering
< 5 ppm
4 ppm
150150 mm2
average
transmission
10 < T < 50 ppm
42,9 +/- 0,2 ppm
150 mm
average
absorption
< 5 ppm
0,63 +/- 0,07 ppm
150 mm
wavefront
flatness
June 24, 2009 - IPNL
< 8 nm RMS
150 mm
3,8 nm RMS
150 mm POSIPOL 2009
Laurent Pinard
VIRGO
5
Introduction - Realizations
VIRGO Mode Cleaner
After optical contact
On the optical bench
5 cm
June 24, 2009 - IPNL
POSIPOL 2009
Laurent Pinard
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LOSSES
Transmission
Absorption
Scattering
Coatings
Multilayer design
Substrate
CLEANING
Sub. Nature
Substrate
POLISHING
(defects, roughness)
Coatings
Deposition
Technique
Substrate
CLEANING
Flatness
Wavefront
Substrate
POLISHING
Coatings
Deposition
Technique
June 24, 2009 - IPNL
Mirror
Cleaning
POSIPOL 2009
Laurent Pinard
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Substrate Choice and Substrate Preparation
Polishing / Scattering
Incident
Beam
Specular
Reflection
Scattering Sources
• Roughness
• Scratches
• Holes
• Inclusions
• Bubbles
1
10
June 24, 2009 - IPNL
Inclusions
Bubbles
• Particles
(Dust)
Clean Environment
Roughness (Å)
Dust
Holes
Roughness
Scattered Light
Scattering
(ppm)
Specular
Transmission
#1
#130
POSIPOL 2009
Laurent Pinard
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Substrate Choice and Substrate Preparation
American, Australian,
French companies
Roughness Micropolished Substrate
Optical Profilometer MICROMAP (proto unique in Europe)
June 24, 2009 - IPNL
POSIPOL 2009
Laurent Pinard
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Substrate Choice and Substrate Preparation
Defects Detection
Scan on 300 mm max, measured area 500*500 µm2 , threshold 0,3 µm
June 24, 2009 - IPNL
POSIPOL 2009
Laurent Pinard
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Substrate Choice and Substrate Preparation
Defects Detection
Scratches/ Holes
June 24, 2009 - IPNL
POSIPOL 2009
Laurent Pinard
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Substrate Choice and Substrate Preparation
Defects Detection - CLEANING
Bad Cleaning : > 106 defects on Ø 200 mm (drying)
June 24, 2009 - IPNL
POSIPOL 2009
Laurent Pinard
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Substrate Choice and Substrate Preparation
Defects Detection - CLEANING
Good Cleaning: 30 defects on Ø 100 mm
June 24, 2009 - IPNL
POSIPOL 2009
Laurent Pinard
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Substrate Choice and Substrate Preparation
Flatness – Wavefront improvement
Corrective Coating
Add silica to fill the holes
Ion Source
Robot
- Flat Surface (< 1 nm RMS)
Advanced Virgo
Substrat in
translation
mask
Sputtered
Atoms
Silica target
Interferometer
June 24, 2009 - IPNL
POSIPOL 2009
Laurent Pinard
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Substrate Choice and Substrate Preparation
Flatness – Wavefront improvement
Substrate 156 mm VIRGO type
Before correction (120 mm)
3.3 nm R.M.S.
16 nm P.V.
June 24, 2009 - IPNL
After correction (120 mm)
0.98 nm R.M.S.
10 nm P.V.
Microroughness preserved (0,5 Å RMS)
POSIPOL 2009
Laurent Pinard
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Substrate Choice and Substrate Preparation
Flatness – Wavefront improvement
Ion Beam Polishing : remove « bumps» with an ion beam
Very good flatness on large area (US company)
Microroughness higher (1,6 Å RMS)
June 24, 2009 - IPNL
POSIPOL 2009
Laurent Pinard
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Substrate Choice and Substrate Preparation
Shape realization : « Mexican hat »
“Flat” Beam
Gaussian Beam
“Flat” beam
Gaussian Beam
June 24, 2009 - IPNL
POSIPOL 2009
Laurent Pinard
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Substrate Choice and Substrate Preparation
Shape realization : « Mexican hat »
1600
Epaisseur de silice (nm)
1400
profil théorique
profil expérimental
1200
1000
800
600
400
IDEAL Mexican hat
200
0
-15
-10
-5
0
5
10
15
Rayon (mm)
Error compared to the theoretical profil :
10 nm in central area (Ø < 14 mm)
100 nm on the edges (14 mm < Ø < 26 mm)
50 mm Mirrors for Caltech (USA)
June 24, 2009 - IPNL
POSIPOL 2009
Laurent Pinard
LMA Mexican hat
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Ion Beam Sputtering - IBS
Deposition technique used all over the world to realize low-loss coatings
Substrate
Assist
Source
O2
+
+
-
Ar
-
-
+
+
-
Sample Holder
+
-
(Simple rotation)
+
200 eV
Neutralizor
Quartz
Sputtered
Particles
Targets
SiO2/Ta
+
+
+
-
O2
1 keV
-
+
+
-
-
+
+
- -
Neutralizor
June 24, 2009 - IPNL
POSIPOL 2009
Laurent Pinard
Sputtering
Source
Ar
Ar
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Ion Beam Sputtering - IBS
 IBS coater at LMA : 0.6*0.6*0.8 m3
 Installed in a class 1 clean room
 «Clean» pumping : (no H20, oil…)
: 1st IBS coater in France (1986)
Cryopumps/ Dry pumps
 Ultra pure targets (> 99,999 %)
 Drawback : deposition speed very low (< 1Å/s)
for Ar atomic %age low
Otherwise Absorption increase
 Component diameter up to 80 mm
June 24, 2009 - IPNL
POSIPOL 2009
Laurent Pinard
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Ion Beam Sputtering - IBS
“VIRGO” Coater : 2.2*2.2*2.4 m3 – Unique in Europe
Coating capacity 1m , thickness uniformity #6.10-3
June 24, 2009 - IPNL
POSIPOL 2009
Laurent Pinard
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Mirror : multidielectric coating
 Mirror : multilayer of dielectric thin films (oxides)
 The optical properties of the multilayers depends on the interferences between
the different layers and on the layer nature
Optical path différences: l /2 l /2 3l /2 3l /2 5l /2 5l /2
Opt Thk = l/4
no
nH > no
nL < nH
air
l/2
High index
0
Low index
l/2
nH > nL
0
nL < nH
l/2
nH > nL
High index
Low index
High index
0
Substrate
nS < nH
June 24, 2009 - IPNL
Constructive
interferences
POSIPOL 2009
Laurent Pinard
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Mirror : multidielectric coating
Multilayer of quarter wave dielectric coatings of high (H-Ta2O5) and low (L-SiO2)
refraction index : (HL)x HLL
(
1 - (n /n )
R=
(1 + (n /n )
2x
H
H
B
B
. n 2H /n S
2x
. n 2H /n S
)
)
R > 99.9% - limited by the optical losses (T, A, S)
2
100
6 couches
2
90
14 couches
26 couches
80
nH - nB
l =  . l0 . arcsin
nH + n B
70
Reflectance (%)
60
50
l
40
30
 Advantages :
20
- High reflectivity (> 99.9 %)
10
l0
- Low absorption loss
0
(Visible, IR : << 10 ppm)
700
800
900
1000
1100
1200
1300
1400
 Drawbacks :
Longueur d’onde (nm)
- Multilayer (HL)x HLL
(> 30 layers, deposition time long)
- High reflectivity on a narrow band (l = 250 nm - depend on the refraction index contrast)
June 24, 2009 - IPNL
POSIPOL 2009
Laurent Pinard
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Mirrors Optical Performances
 Transmission : possible to have T< 1 ppm and to measure it
 Absorption (@ 1064 nm) : 0,3 ppm (@633 nm #3 ppm)
Problem = measuring absorption levels so low : « mirage effect » (photothermy)
Pro
be
B
63 eam
3n
m He-N
Focus Lenses
e
Pump Beam YAG
1064 nm
(energetic)
Chopper
Lock-in
Amplifier
June 24, 2009 - IPNL
POSIPOL 2009
Laurent Pinard
Po
De sitio
tec n
tor
Sample
(normal incidence)
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Mirrors Optical Performances
Absorption Bench
 Relative Measurement (reference sample)
 Sensitivity (@ 1064 nm) :
surface absorption : 0,02 ppm
bulk absorption : 0,1 ppm/cm
d
June 24, 2009 - IPNL
POSIPOL 2009
Laurent Pinard
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Mirrors Optical Performances
 Scattering : # 5 ppm on optical components (small or large dimensions)
Maps on  400 mm
SNR # 10-9
Scattering level < 1ppm
June 24, 2009 - IPNL
POSIPOL 2009
Laurent Pinard
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Mirrors Optical Performances
Scattering-Cleanliness
All the mirror production steps in clean room
Filter
99,X
Absolute Filter
99,9999 %
Filtres
Particles > 0,1 µm
Air Propre
Clean
Air
+
Flux
Laminar
Flux
Laminaire
Fan
June 24, 2009 - IPNL
POSIPOL 2009
Laurent Pinard
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Mirrors Optical Performances
Scattering-Cleanliness
Laminar Flux
Turbulent Flux
Dust
Particles carried away by the
recycled flux
Low probability to
contaminate the sample
June 24, 2009 - IPNL
High Probability
to contaminate the sample
POSIPOL 2009
Laurent Pinard
28
Mirrors Optical Performances
Particles counting
Scattering-Cleanliness
Scattering maps @ 633 nm
47 particles (< 0,3 µm)
June 24, 2009 - IPNL
POSIPOL 2009
Laurent Pinard
Average scattering 0.3 ppm
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Mirrors Optical Performances
Scattering-Cleanliness
Particles counting
Scattering maps @ 633 nm
3000 particles of 1 µm
June 24, 2009 - IPNL
Average scattering 7 ppm
(multiplied par 23)
POSIPOL 2009
Laurent Pinard
30
Mirrors Optical Performances
Scattering-Cleanliness
1E-04
B.R.D.F (sr
-1
)
1 µm
0,5 µm
0,2 µm
0,1 µm
1E-05
1E-06
Substrate Level
1E-07
0
June 24, 2009 - IPNL
100
200
300
400
500
Number of particles . cm-2
POSIPOL 2009
Laurent Pinard
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Mirrors Optical Performances
Scattering-Cleanliness
Main problem for mirrors users : keep the loss level low
- manipulate in clean conditions (clean room)
- never touch the surface
- clean vacuum in cavities (no turbulences)
Virgo mirror
Average Scattering 4 ppm
After use
Average Scattering 25 ppm
June 24, 2009 - IPNL
POSIPOL 2009
Laurent Pinard
32
Mirrors Optical Performances
Scattering-Cleanliness
 Polluted Mirror : in general reversible
Cleaning (wet) possible if mirror dismountable (not possible in Virgo)
 Other solution for the cleaning : removable polymer film « First Contact »
(http://www.photoniccleaning.com/)
June 24, 2009 - IPNL
POSIPOL 2009
Laurent Pinard
33
Mirrors Optical Performances
 Liquid, dry in ¼ hour
 Can be put by spray or with a brush
 2 important properties
 Protect optical surfaces (during mounting,…)
 Can clean optical surfaces
Spray
Brush
June 24, 2009 - IPNL
POSIPOL 2009
Laurent Pinard
34
Mirrors Optical Performances
50 mm Mirror after classical cleaning
Scattering : 6 ppm
Absorption : 1.91 ppm
50 mm Mirror polluted
Scattering : 25 ppm
Absorption : 5 ppm
50 mm Mirror, after putting and removing
the film ‘First Contact'
Scattering : 6-6.5 ppm
Absorption : 1.73 ppm
The film has cleaned and
POSIPOL 2009
June
24,
2009
IPNL
Laurent Pinard
did not let absorbing waste on the surface
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