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Jean-Marie MACKOWSKI Université Claude Bernard Lyon 1 SMA-VIRGO Bât 213 22, Bd Niels Bohr 69622 Villeurbanne Cedex [email protected] Phone : + 33 04 72 43 26 69 Fax : + 33 04 78 89 19 36. TODAY MENU. COATING DEFINITION DIELECTRIC COATINGS Quaterwave Rule Some Useful Designs - PowerPoint PPT Presentation
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Univ
ers
ité
Lyon I
NATO/ASI and Euro Summer School September 16-27, 2002 JM.M
SMASMASMASMA
OPTICS IN ASTROPHYSICSOPTICS IN ASTROPHYSICSCoatingsPrinciplesCoatingsPrinciples
Jean-Marie MACKOWSKI
Université Claude Bernard Lyon 1SMA-VIRGO
Bât 21322, Bd Niels Bohr
69622 Villeurbanne Cedex
[email protected] : + 33 04 72 43 26 69
Fax : + 33 04 78 89 19 36
Jean-Marie MACKOWSKI
Université Claude Bernard Lyon 1SMA-VIRGO
Bât 21322, Bd Niels Bohr
69622 Villeurbanne Cedex
[email protected] : + 33 04 72 43 26 69
Fax : + 33 04 78 89 19 36
Univ
ers
ité
Lyon I
NATO/ASI and Euro Summer School September 16-27, 2002 JM.M
SMASMASMASMA
OPTICS IN ASTROPHYSICSOPTICS IN ASTROPHYSICSCoatingsPrinciplesCoatingsPrinciples
Univ
ers
ité
Lyon I
NATO/ASI and Euro Summer School September 16-27, 2002 JM.M
SMASMASMASMA
OPTICS IN ASTROPHYSICSOPTICS IN ASTROPHYSICSCoatingsPrinciplesCoatingsPrinciples
TODAY MENU TODAY MENU
TOMORROW MENU TOMORROW MENU
Coatings Deposition techniquesPerformances & limitations
Coatings Deposition techniquesPerformances & limitations
COATING DEFINITION
DIELECTRIC COATINGSQuaterwave Rule
Some Useful Designs
METALLIC COATINGSSilver, Aluminum, Gold Reflectors
Passivation LayersAntireflection of a Metal
Enhanced reflectors by Dielectric Layers
COATING DEFINITION
DIELECTRIC COATINGSQuaterwave Rule
Some Useful Designs
METALLIC COATINGSSilver, Aluminum, Gold Reflectors
Passivation LayersAntireflection of a Metal
Enhanced reflectors by Dielectric Layers
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NATO/ASI and Euro Summer School September 16-27, 2002 JM.M
SMASMASMASMA
OPTICS IN ASTROPHYSICSOPTICS IN ASTROPHYSICSCoatingsPrinciplesCoatingsPrinciples
Optical coating consist of a layer or series of layers of different materials,
that are deposited over the surface to be treated.The desired properties of the coating
are achieved by a mixture of interference and intrinsic properties of the materials that are used
Optical coating consist of a layer or series of layers of different materials,
that are deposited over the surface to be treated.The desired properties of the coating
are achieved by a mixture of interference and intrinsic properties of the materials that are used
Incident
Transmitted
Surface
Reflected
CoatingCoating
OPTICAL COATINGS 2.
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SMASMASMASMA
OPTICS IN ASTROPHYSICSOPTICS IN ASTROPHYSICSCoatingsPrinciplesCoatingsPrinciples
COATINGS
INCLUDING
DIELECTRIC LAYERS ONLY
COATINGS
INCLUDING
DIELECTRIC LAYERS ONLY
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OPTICS IN ASTROPHYSICSOPTICS IN ASTROPHYSICSCoatingsPrinciplesCoatingsPrinciples
Using interference properties means creating and changing the shape of interference fringes
Thin films GiveThe desirableBroad fringesThat we need
95.5
96.0
96.5
97.0
97.5
400 500 600 700
Transmittance (%)
Wavelength (nm)
Thick materialsGive fringes tooClosely spaced
To be useful
95.5
96.0
96.5
97.0
97.5
400 500 600 700
Transmittance (%)
Wavelength (nm)
Glass 100 µm
Glass 1 µm
WHY THIN AND NOT THICK FILMS ?WHY THIN AND NOT THICK FILMS ?
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OPTICS IN ASTROPHYSICSOPTICS IN ASTROPHYSICSCoatingsPrinciplesCoatingsPrinciples
Quaterwave Layers give Maximum interference
Effect
Half Layers are Absentee Layers-They have No Effect
Dielectric Layers Become Weaker whit Increasing
Wavelenght
Metal Layers become Stronger with Increasing
Wavelenght
Quaterwave Layers give Maximum interference
Effect
Half Layers are Absentee Layers-They have No Effect
Dielectric Layers Become Weaker whit Increasing
Wavelenght
Metal Layers become Stronger with Increasing
Wavelenght
BASIC DESIGN PRINCIPLES
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OPTICS IN ASTROPHYSICSOPTICS IN ASTROPHYSICSCoatingsPrinciplesCoatingsPrinciples
A quarterwave: f
0
n4H,L
transforms the surfacefollowing the rule :
s
2f
t nnn
A quarter stack with x layers of H and (x-1) layers of L:
s0 nLHHLHLn
has reflectance
S)1x(2
L
x2H
o
S)1x(2
L
x2H
o
n)n()n(
n
n)n()n(
nR
0is the working wavelenght
stf nandn,n are the refractive indexes of film, transformed surface, and substrat, respectively
THE QUATERWAVE RULE THE QUATERWAVE RULE
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OPTICS IN ASTROPHYSICSOPTICS IN ASTROPHYSICSCoatingsPrinciplesCoatingsPrinciples
THE QUATERWAVE RULE ...
THE QUATERWAVE RULE ...
Interference calculations for two waves are very simple when the waves are combined Are exactly in phase or exactly out of phase. In the former case the resultant amplitudeIs simply given by the sum of individual amplitudes while in the latter it is the difference
of amplitudes.All others cases are intermediate.
The phase shift on reflection at a simple interface between two dielectric media is either
Zero or 180° ( / 2).
The phase shift suffered by a wave traveling through thickness d of a thin film is given by- 2 n /
The minus sign indicates a phase lag.This is such an important quantity that its magnitude is given the symbol :
=2 n d /
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OPTICS IN ASTROPHYSICSOPTICS IN ASTROPHYSICSCoatingsPrinciplesCoatingsPrinciples
Reflected light:Beams interfere constructively
Amplitude reflectanceof light:
< 0n0-n1
n0+n1
> 0n1-n2
n1+n2
n1 > no
n2 < n1
Thin film
Substrate
/2 /2 = /4+0+/4:
no air/2
REFLECTION OF SINGLE FILM
REFLECTION OF SINGLE FILM
Film Thickness is Quaterwave
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OPTICS IN ASTROPHYSICSOPTICS IN ASTROPHYSICSCoatingsPrinciplesCoatingsPrinciples
Beams interfere destructively
Amplitude reflectanceof light:
< 0n0-n1
n0+n1
< 0n1-n2
n1+n2
n1 > no
n2 > n1
Thin film
Substrate
/2 = /4+ + /4:
no air/2
Thin film thickness =
ANTIREFLECTION OF SINGLE FILM ANTIREFLECTION OF SINGLE FILM
/2
Reflection = 0 if no / n1 = n1 / n2 n1 = (no n2)1/2
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OPTICS IN ASTROPHYSICSOPTICS IN ASTROPHYSICSCoatingsPrinciplesCoatingsPrinciples
no
nH > no
nL < nH
nH > nL
nL < nH
nH > nL
nS < nH
: /2 /2 3/2 3/2 5/2 5/2
/2
/2
/2
0
0
0
airno
nH > no
nL < nH
nH > nL
nL < nH
nH > nL
nS < nH
high index
high index
low index
low index
Substrate
high index
DIELECTRIC MIRRORS DIELECTRIC MIRRORS Beams interfere
constructivelyBeams interfere constructively
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OPTICS IN ASTROPHYSICSOPTICS IN ASTROPHYSICSCoatingsPrinciplesCoatingsPrinciples
QUATERWAVE STACK IS A BASIC BUILDING BLOCK QUATERWAVE STACK IS A BASIC BUILDING BLOCK 23-Layer quaterwave stack centered on 800 nm
The ripple is usually removed by adding several layers at each end and refining them into a matching structure
Ripple
Notch Filter
Longwave passor Dichroic Filter
High Reflectance
Shortwave passor Dichroic Filter
0
20
40
60
80
100
200 400 600 800 1000 1200 1400
Transmittance (%)
Wavelength (nm)
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OPTICS IN ASTROPHYSICSOPTICS IN ASTROPHYSICSCoatingsPrinciplesCoatingsPrinciples
RIPPLE CONTROL RIPPLE CONTROL 23-Layer quaterwave stack centered on 800 nm
Without Ripple control
0
20
40
60
80
100
200 400 600 800 1000 1200 1400
Transmittance (%)
Wavelength (nm)
23-Layer quaterwave stack centered on 800 nm With Ripple control (Matching Layers)
Quaterwave stack L (HL)^11 E.M
E.M
Quaterwave stack L (HL)^11I.M E.M
(2L.1H)^2 (.1H2L)^2
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OPTICS IN ASTROPHYSICSOPTICS IN ASTROPHYSICSCoatingsPrinciplesCoatingsPrinciples
BROADBAND REFLECTOR BROADBAND REFLECTOR
0
20
40
60
80
100
350 400 450 500 550 600 650 700 750 800 850 900 950 1000
Reflectance (%)
Wavelength (nm)
90
92
94
96
98
100
350 400 450 500 550 600 650 700 750 800 850 900 950 1000
Reflectance (%)
Wavelength (nm)
(HL)^5 1.2L (1.4H 1.4L)^5 1.4H
L index : 1.35Cryolite :Na3ALF6
H index : 2.35ZnS
23 Layers
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OPTICS IN ASTROPHYSICSOPTICS IN ASTROPHYSICSCoatingsPrinciplesCoatingsPrinciples
MULTIPLE-CAVITY FILTER MULTIPLE-CAVITY FILTER
0
20
40
60
80
100
990 995 1000 1005 1010
Transmittance (%)
Wavelength (nm)A simple cavity consists of a half wave layer surrounded by to reflectors
This gives a narrow band of transmission.Better pass band can be achieved by coupling cavities into multiple-cavity filters
Here a three cavity: {(HL)^5 HH (LH)^5}^3 giving a band pass of 1.2 nm.
Single cavity Two-cavity
Three-cavity
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OPTICS IN ASTROPHYSICSOPTICS IN ASTROPHYSICSCoatingsPrinciplesCoatingsPrinciples
Characteristics move To shorterWavelenght and become@ 45° of incidence : Stronger for s-polarizationAnd weaker for p-polarization
The green curve is given at Normal incidence.
OBLIQUE INCIDENCE OBLIQUE INCIDENCE
At oblique incidence the path difference between the beams is reduced and
their amplitudes for s-polarized light is increased and for p-polarized light decreased.
0
20
40
60
80
100
300 400 500 600
Transmittance (%)
Wavelength (nm)
G
R
B
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OPTICS IN ASTROPHYSICSOPTICS IN ASTROPHYSICSCoatingsPrinciplesCoatingsPrinciples
WIDE-ANGLE ANTIREFLECTION COATING WIDE-ANGLE ANTIREFLECTION COATING
0
1
2
3
4
5
0 10 20 30 40 50 60 70
Reflectance (%)
Incident Angle (deg)
Here an antireflection coating on glass for a single wavelenght (510 nm) At angles of incidence up to 5O° and both polarizations.
9 layers of MgF2, Al2O3 and TiO2
p-Polarizations-Polarization
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OPTICS IN ASTROPHYSICSOPTICS IN ASTROPHYSICSCoatingsPrinciplesCoatingsPrinciples
NON-POLARIZING BEAM SPLITTER
NON-POLARIZING BEAM SPLITTER
The design of dielectric coatings to have equal p- and s-polarization over a large spectralregion is exceptionally difficult.
Here a simple 8 layers 45° beam splitter for 500 to 600 nm using TiO2, Al2O3 and SiO2
0
20
40
60
500 600
Reflectance (%)
Wavelength (nm)
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Lx, Hz (HL)^10 Stack Performances Lx, Hz (HL)^10 Stack Performances
0
20
40
60
80
100
400 500 600 700
Transmittance (%)
Wavelength (nm)
L (HL)^10
H (HL)^10
LL (HL)^10
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ELECTRIC FIELD DISTRIBUTION ELECTRIC FIELD DISTRIBUTION
20
40
60
-0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
Electric Field (V/m)
Optical Distance from Medium
Design2: Parallel Electric Field
20
40
60
-1 0 1 2 3 4 5 6
Electric Field (V/m)
Optical Distance from MediumTHE FIRST LAYERS OF ALL DESIGNS
ALL LAYERS
L (HL)^10
H (HL)^10
LL (HL)^10
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Total Layer Absorptance (%)
0.0005
0.0004
0.0003
0.0002
0.0001
0.0000
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Total Layer Absorptance (%)
0.00008
0.00007
0.00006
0.00005
0.00004
0.00003
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
COMPONENT ABSORPTION VS DESIGN COMPONENT ABSORPTION VS DESIGN
0 = 800 nm
0 = 550 nm
Layer number
Layer number
L(HL)^10 H(HL)^10 LL(HL)^10
0.000020.00001
0.00000
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OPTICS IN ASTROPHYSICSOPTICS IN ASTROPHYSICSCoatingsPrinciplesCoatingsPrinciples
20
40
60
80
100
-1 0 1 2 3 4 5 6
Electric Field (V/m)
Optical Distance from Medium
L(HL)^10- R=800 nm, C=550nmL(HL)^10 R=800 nm, C=550 nm
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OPTICS IN ASTROPHYSICSOPTICS IN ASTROPHYSICSCoatingsPrinciplesCoatingsPrinciples
0
20
40
60
80
100
0 1 2 3 4 5 6
Electric Field (V/m)
Optical Distance from Medium
H(HL)^10 B=800 nm, C=550 nmH(HL)^10 B=800 nm, C=550 nm
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OPTICS IN ASTROPHYSICSOPTICS IN ASTROPHYSICSCoatingsPrinciplesCoatingsPrinciples
20
40
60
80
100
-1 0 1 2 3 4 5 6
Electric Field (V/m)
Optical Distance from Medium
LL(HL)^10 G=800 nm, C=550 nm
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MULTIDIELECTRIC MIRRORS MULTIDIELECTRIC MIRRORS Advantages :
- High reflectance (> 99.9 %)- Low absorption loss (Visible, IR : < 10 ppm)
Drawbacks : - Multilayers (HL) x HLL (> 30 layers, deposition time long)- High reflectance over a short wavelength domain ( = 250
nm)
0
10
20
30
40
50
60
70
80
90
100
700 800 900 1000 1100 1200 1300 1400
Wavelength (nm)
Ref
lect
ance
(%
)
6 layers
14 layers
26 layers
0
LH
LH
nn
nnarcsin
= . 0 .
2
S2H
2xLH
2
S2H
2xLH
/nn .)/n(n 1
/nn .)/n(n -1 R
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OPTICS IN ASTROPHYSICSOPTICS IN ASTROPHYSICSCoatingsPrinciplesCoatingsPrinciples
COATINGSINCLUDING
METALLIC LAYERS
COATINGSINCLUDING
METALLIC LAYERS
The most popular in Astronomy
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OPTICS IN ASTROPHYSICSOPTICS IN ASTROPHYSICSCoatingsPrinciplesCoatingsPrinciples
0
20
40
60
80
100
0 2000 4000 6000 8000 10000
Reflectance (%)
Wavelength (nm)
100 nm of Silver (R), Aluminum (G), Gold (B) on glass100 nm of Silver (R), Aluminum (G), Gold (B) on glass
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OPTICS IN ASTROPHYSICSOPTICS IN ASTROPHYSICSCoatingsPrinciplesCoatingsPrinciples
100 nm of Silver (R), Aluminum (G), Gold (B) on glass100 nm of Silver (R), Aluminum (G), Gold (B) on glass
0
20
40
60
80
100
0 200 400 600 800 100012001400160018002000
Reflectance (%)
Wavelength (nm)
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100 nm of Silver (R), Aluminum (G), Gold (B) on glass100 nm of Silver (R), Aluminum (G), Gold (B) on glass
97.5
98.0
98.5
99.0
99.5
100.0
6000 7000 8000 9000 10000
Reflectance (%)
Wavelength (nm)
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OPTICS IN ASTROPHYSICSOPTICS IN ASTROPHYSICSCoatingsPrinciplesCoatingsPrinciples
B
a
bBULK
METALBULK
METAL
DIELECTRIC Layer (QW)DIELECTRIC Layer (QW)
0
20
40
60
80
100
0 1000 2000 3000 4000
Reflectance (%)
Wavelength (nm)
SiO2-QW/Ag-100 nm/SIO2-Qw
Ag-100 nm
REFLECTANCE OF A METAL FILM WITH PASSIVATION LAYER
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Reflector
Dielectric phase Matching layer
Metal layer
a b
0
20
40
60
400 500 600 700
Reflectance (%)
Wavelength (nm)
Cr 10 nm / MgF2 100 nm / Al 3 nm
Cr - 10 nm on glass
ANTIREFLECTION OF A METAL FILM
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OPTICS IN ASTROPHYSICSOPTICS IN ASTROPHYSICSCoatingsPrinciplesCoatingsPrinciples
V
Metal layer
High index
Low index
0
20
40
60
80
100
200 400 600 800 1000 1200 1400 1600 1800 2000
Reflectance (%)
Wavelength (nm)
(HL)^3-M-(LH)^3
INDUCED TRANSMISSION IN A METAL FILM
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86
88
90
92
94
96
98
100
340 360 380 400 420 440 460 480 500 520 540
Reflectance (%)
Wavelength (nm)
Enhanced 100 nm of aluminum protected by dielectric layersL (low index) : SiO2 or MgF2 & H (high index) : TiO2Enhanced 100 nm of aluminum protected by dielectric layersL (low index) : SiO2 or MgF2 & H (high index) : TiO2
Al
Al+H L
Al+(H L)^2
Al+(H L)^3
Al+(H L)^3
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70
75
80
85
90
95
100
340 360 380 400 420 440 460 480 500 520 540
Reflectance (%)
Wavelength (nm)
Enhanced 100 nm of aluminum protected by dielectric layersL (low index) : SiO2 , H (high index) : TiO2Enhanced 100 nm of aluminum protected by dielectric layersL (low index) : SiO2 , H (high index) : TiO2
Al+(HL)^3R=99,57%
Al+(HL)^20T=99,54%
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METALLIC MIRRORS METALLIC MIRRORS Advantages : High reflectance (> 90 %)
- over a large range of incident angles- over a wide band of wavelength (UV, Visible, IR)
Drawback : High absorption loss
Al
Ag
Au
22
22
kn)(1
kn)-(1 R
Al : good for U.V. (R > 90 %), adhereon most substrates, passivation necessary (oxidation)
Ag : most popular, easy to deposit, highest reflectance in visibleand I.R., tarnish rapidly,protection necessary
Au : best material in I.R. (> 700 nm), high reflectance, does not tarnish