Jean-Marie MACKOWSKI Université Claude Bernard Lyon 1 SMA-VIRGO Bât 213 22, Bd Niels Bohr

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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

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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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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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COATINGS

INCLUDING

DIELECTRIC LAYERS ONLY

COATINGS

INCLUDING

DIELECTRIC LAYERS ONLY

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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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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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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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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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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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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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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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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

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100

200 400 600 800 1000 1200 1400

Transmittance (%)

Wavelength (nm)

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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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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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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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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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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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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


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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60

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100

-1 0 1 2 3 4 5 6



L(HL)^10- R=800 nm, C=550nmL(HL)^10 R=800 nm, C=550 nm

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0

20

40

60

80

100

0 1 2 3 4 5 6



H(HL)^10 B=800 nm, C=550 nmH(HL)^10 B=800 nm, C=550 nm

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40

60

80

100

-1 0 1 2 3 4 5 6



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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COATINGSINCLUDING

METALLIC LAYERS

COATINGSINCLUDING

METALLIC LAYERS

The most popular in Astronomy

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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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0

20

40

60

80

100

0 200 400 600 800 100012001400160018002000

Reflectance (%)

Wavelength (nm)

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97.5

98.0

98.5

99.0

99.5

100.0

6000 7000 8000 9000 10000

Reflectance (%)

Wavelength (nm)

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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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V

Metal layer

High index

Low index

0

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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

Jean-Marie MACKOWSKI Université Claude Bernard Lyon 1 SMA-VIRGO Bât 213 22, Bd Niels Bohr

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