High Stability Optical Coatings By Employing …High Stability Optical Coatings By Employing...

High Stability Optical CoatingsBy Employing Gradient Index Designs

Kai Starke, Cutting Edge Coatings GmbHDetlev Ristau, Laser Zentrum Hannover e.V.

2Confidential

Motivation

Coatings for High Performance Lasers

Few-cycle pulse duration laser, one-octave chirped mirror, MBI Berlin

Multi-kW disk laser

� High Damage Resistance

� Defined Group Delay Dispersion

� Highest Reflectivity

� Very Low Optical Losses

SVC TechCon Chicago April 16-21,2011

3Confidential

Outline

1. IBS Coating Technology

– Co-Deposition Principle

– Advanced Optical Monitoring

2. Absorption Shift

3. LIDT Results on Gradient Index Coatings

– cw-Radiation at 1064nm

– fs-pulsed Radiation around 800nm

– ns-pulsed Radiation at 266, 355 and 1064nm


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Process Principle

vacuumchamber

P R E 0401 8

shutte rsubstrate rotation

ion source

zone target

linear motion

vacuumchamber

P R E 0401 8

shutte rsubstrate rotation

ion source

zone target

linear motion

M. Lappschies et al., Appl. Opt. 45 (2006).

IBS Process Variation

• Ion-beam sputtering (IBS)

coating system equipped

with zone target

• Mixtures of oxide materials

�� discrete layer stacks

�� gradient coatings (Rugate)

Alternating Layers Blended Materials


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Zone Target Calibration

100 80 60 40 20 01,4

1,6

1,8

2,0

2,2 400nm 600nm

Ref

ract

ive

inde

x

Target position, steps x 103

6500

2950

0

4400

048

252

5250

056

752

6100

0

7550

0

9850

0

250 200 150 100 50 0

Zr Si

ZrxSi1-xO2


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Broadband Monitoring System

• Spectrum of rotating substrate

• Spectrum range > 1 octave

• DUV Spectra down to 230nm

• Typical accuracy few nm

• Integration in system control

Process Control

Principle of in-situ broad-band optical monitoring

� Realization of complex designs

� Test coating runs obsolete

� Fully automated production


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Optical Monitoring

Front view of coating system

Rugate mirror @ 266nm

• ZrO2/SiO2-mixture

• >350 layers, ≈ 5nm

• design-loaded onto

coating system

• controlled by broad-

band optical monitoring

0 40 80 120 160 200 240 280 320 360

1.44

1.52

1.6

1.68

1.76

1.84

1.92

2

2.08

2.16 © LZH

Vilnius, Lithuania

In-situ broad-band optical monitoring


Absorption Shift

„digital“ approximation

� 50 layers with 0,04 QWOT

� 4,6 nm TiO2/ 7,2 nm SiO2

300 400 500 600 700 800 900 1000 1100 12000,0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1,0

400 600 800 1000 1200

1,5

2,0

2,5

3,0

refr

activ

e in

dex

n

wavelength [nm]

TiO2

quasi mixture SiO

2

tran

smitt

ance

wavelength [nm]

measurement quasi single layer approximation stack design theory

co-deposited mixture (TixSi1-xO2)

� utilization of Ti/Si- zone target

� 40% content of TiO2 in mixture

300 400 500 600 700 800 900 1000 1100 12000,0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1,0

300 350 400 450 500

0,1

0,2

0,3

0,4

0,5

ext

inct

ion

k

wavelength [nm]

pur TiO2

deduction according to TiO

2 content

Ti0.4

Si0.6

O2

tran

smitt

ance

wavelength [nm]

measurement n&k data fit quasi single layer approximation

25nm

Band edge broadened Band edge shifted

Two representations of a mixed TiO2/SiO2-layer (2 [email protected])

8SVC TechCon Chicago April 16-21,2011

Confidential

9Confidential

Example: Ta2O5 for DUV

Mixture Materials:

• Intermediate n

• blue-shift of

absorption band

• corresponding

results for TiO2,

HfO2, Al2O3, ZrO2,

Nb2O5, Y2O3 etc.

� UV-extension of

coating materials

� Novel design possibilities using

artificial materials with defined n Guiding mirror (266nm, 45°)AR 1ω and 2ω, Ta2O5/SiO2 mixture


cw-Damage Resistance

ME ASU REM ENT FACI LITYSP ECIF ICAT IONS

Laser waveleng th 10 64 nmAngle of inciden ce ap prox. 0 radPolar isation sta te line arRepe tition rate up to 30 kHz

Max. pulse ener gy 4 m J @ 1 kH zBeam profile in target plan eTE M00, multi longitudina lSpot diameter ( 1/e2) 7.5 µmPulse duration ( FWHM) 17 0 ns @ 1 k HzSites per specim en 15 4, hexagon al close pa ckedSepa ration of te st sites 1.2 mm

Dama ge detecti on on line: transm ission of H R mirrorsoff line: Noma rski-micro scopyPulse number d eterminatio nco mputer ass isted pulse countingde vice

SP ECIM EN P REP ERAT IONType of specime n (e-beam )HR mirrors a t 1064 nm on BK7su bstrates, m iscellaneo us coatingma terials

Desig ns qu arter-wave stacksManu facturer La ser Zentru m Hannov er e.V. andLa ser Optik G mbHCoati ng process co nventional e-beam PV DType of specime n (IBS) HR mirrors a t 1064 and 532 nm o n

10

400 600 800 1000 12000,6

0,7

0,8

0,9

1,0

T measured

Tra

nsm

ittan

ce

Wavelength [nm]

ZrxSi1-xO2 AR coatings on lenses, high power NIR lasers

0 0.2 0.4 0.6 0.8 1 1.2

Optical Thickness [µm]

1.44

1.52

1.6

1.68

1.76

1.84

1.92

2

2.08

2.16

n

© LZH

Gradient-index Design

AR1030-1070, HT 532/633

Total thickness 0.75µm,

18lay., ZrO2 content 0..90%

[email protected]

Double-sided AR sample


Confidential

cw-Irradiation @ 1.070nm

10kW, 10min without changes

fs-Damage Effects

ME ASU REM ENT FACI LITYSP ECIF ICAT IONS

Laser waveleng th 10 64 nmAngle of inciden ce ap prox. 0 radPolar isation sta te line arRepe tition rate up to 30 kHz

Max. pulse ener gy 4 m J @ 1 kH zBeam profile in target plan eTE M00, multi longitudina lSpot diameter ( 1/e2) 7.5 µmPulse duration ( FWHM) 17 0 ns @ 1 k HzSites per specim en 15 4, hexagon al close pa ckedSepa ration of te st sites 1.2 mm

Dama ge detecti on on line: transm ission of H R mirrorsoff line: Noma rski-micro scopyPulse number d eterminatio nco mputer ass isted pulse countingde vice

SP ECIM EN P REP ERAT IONType of specime n (e-beam )HR mirrors a t 1064 nm on BK7su bstrates, m iscellaneo us coatingma terials

Desig ns qu arter-wave stacksManu facturer La ser Zentru m Hannov er e.V. andLa ser Optik G mbHCoati ng process co nventional e-beam PV DType of specime n (IBS) HR mirrors a t 1064 and 532 nm o n

( ) κτ⋅⋅+≈ gapEbaF


Confidential

Ti:Sapphire-Laser

Ø 100 µm, 10 Hz W. Rudolph et al. SPIE 4932, 2003

Damage threshold of IBS single layers of pure coating material

fs-Damage Effects

3,4 3,5 3,6 3,7 3,8 3,9 4,0 4,1 4,2 4,3

0,4

0,6

0,8

1,0

1,2

1,4

1,6

Dam

age

Thr

esho

ld [J

/cm

2 ]Band Gap Energy [eV]

Band Edge and Damage Threshold of IBS TixSi1-xO2 single layers

*D. Nguyen et al.:Appl. Phys. L. 93, 261903 (2008)


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Ti:Sa-Laser

λ 780nm Ø 200µmτ 230fs


5,5 6,0 6,5 7,0 7,50,5

1,0

1,5

2,0

2,5

3,0

3,5

4,0

4,5

5,0

35fs 100fs 200fs 500fs 1.1ps

Ene

rgy

Den

sity

[J/c

m2 ]

Band Edge [eV]

fs-Damage Effects

L. Jensen et al.: Laser Damage Symposium (2010)


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Damage Threshold of IBS HfxSi1-xO2 single layers

HfO2/SiO2-mixtures

• HfO2 content from

0% to 100%

• Band edge energy

determined with

Tauc-plot


Ti:Sa-Laser

λ 780nm Ø 200µm

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Microstructure Analysis


Analysis of IBS HfxSi1-xO2 QWOT mirror coatings

TEM XRD

H: Hf0.7Si0.3O2

L: SiO2

fs-Damage of Mirrors

15

0,0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1,0

Calculated Damage Level

HR780TiO with 7% Si not annealedV060327_6

50%-LIDT 0%-LIDT

V060327_7 50%-LIDT 0% -LIDT

HR780V060327_3 TiO with 7%SiO (12h@240°C)

50%-LIDT 0%-LIDT

V060327_5 (12h@240°C))

50%-LIDT 0%-LIDT

Ene

rgy

dens

ity [J

/cm

2 ]0 1000 2000 3000 4000

0,01

0,1

1

10

100

Lowest LIDT-Value H=0.258 J/cm2

LID

T [J

/cm

2 ]

optical thickness of layers [nm]

Calculation and Optimization of LIDT

E.g. Standard QWOT Mirror TiO2/SiO2

*M. Jupé et al.:Laser Damage Symposium, Boulder (2009)


Confidential

Ti:Sa-Laser

λ 780nm τ 130fs( ) κτ⋅⋅+≈ gapEbaF

16Confidential

ns-Damage Resistance

0 20 40 60 80 100

0,0

0,2

0,4

0,6

0,8

1,0

Dam

age

prob

abili

ty

Energy density [J/cm²]

Data Fit Damage freq.

cha06038

1000 Pulses

0 100 200 300 400 500

0,0

0,2

0,4

0,6

0,8

1,0

cha06040

1000 Pulses

Dam

age

prob

abili

ty

Energy density [J/cm²]

Data Fit Damage freq.

TiO2/SiO2 (total thickn. 2,46 µm) TiO2/SiO2 (total thickn. 4,42 µm)

Measurement of laser-induced damage threshold (LIDT)acc. ISO 11254, 1.064nm, pulse duration 8ns

� Strongly increased LIDT with ns-pulses

Class. QWOT mirror (TiO2/SiO2)

first damagedsites at 10J/cm²

first damagedsites at 167 J/cm²

Rugate-mirror (TixSi1-xO2)


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Damage Resistance ns-Pulses

Long-term photograph of ns-pulsed laser beam guided by Rugate-mirror (discharge at dust particles)


200 220 240 260 2800,0

0,2

0,4

0,6

0,8

1,0

256 260 264 268 2720,90

0,92

0,94

0,96

0,98

1,00

Ref

lect

ivity

Wavelength [nm]

Standard RISED 1 RISED 2 Rugate


ZrxSi1-xO2: HR 266 using different designs

Standard

QW-Design (HL)20 H

~50% ZrO2 in H-layers

1.7µm

Refractive Index StEp

Down

1: 29l, 1.1µm

2: 39l, 1.5µm

Rugate Design

352l, 2.0µm


Confidential

1 10 100 10000

2

4

6

8

10

12

14

16

18

20

0% L

IDT

[J/c

m2 ]

Number of pulses

QW-Stack RISED 1 RISED 2 Rugate Al

2O

3/SiO

2

19Confidential


Damage threshold of 266nm mirrors with ZrxSi1-xO2 mixturesComparison with Al2O3/SiO2 QWOT mirror

LIDT @ 266nm

• 1.000-on-1

• fp10 Hz

• τ 3,5 ns

• Ø 273 µm


Vilnius, Lithuania

20Confidential


0 200 400 600 800 1000 1200 1400 1600 1800

3,0

3,5

4,0

4,5

5,0

5,5

6,0

6,5

7,0

2,0

2,0

2,5

2,0

2,0

2,0

1,5

1,5

1,5

1,5

100%

95%

70%

80%

RISED

AtmosphereSubstrate

Ref

ract

ive

Inde

x

Phys. Thickness [nm]

1,5


HfxSi1-xO2: HR 355 using different designs approaches

Refractive Index StEp

Down and Standard

QWOT-Design

diff. HfO2 contents

in H-layers,

same level of

reflectivity

21Confidential



L. Jensen et al.:Laser Damage Symposium (2010)

LIDT @ 355nm

• 100 Hz

• 6 ns

• ≈200 µm

Damage threshold of 355nm mirrors with HfxSi1-xO2 mixtures

RISED Stand. 100% Stand. 95% Stand. 80% Stand. 70%0

2

4

6

8

10

12

14

Ene

rgy

Den

sity

[J/c

m²]

LIDT 1-on-1 LIDT 10.000-on-1

22Confidential

Summary

� Oxide mixtures with tailored dispersion

from NIR to DUV by genuine co-sputtering

� Gradient index designs possible with

advanced broad-band optical monitoring

� Usable spectral range extended due to

absorption band shift (Ti, Ta, Nb, Hf, Al)

� Stability of AR and HR with mixture

materials and gradient index coatings

demonstrated


23Confidential

Acknowledgements

German Ministry of Commerce and Technology (BMWi)

Project HoLeBo, ProInno 2, KF0096204DA6

German Ministry of Education and Research (BMBF)

Project OMEX, 13N9102

Innonet, Project TAILOR, 16IN0665 and16IN0667

Regional Government of Lower Saxonia, Innovation Support Action,

Project IBS-PRO, W3-80030147


High Stability Optical Coatings By Employing …High Stability Optical Coatings By Employing...

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