Laser damage resistance of optical coatings in the sub-ps regime ... · Optical Coatings for Laser...

O p t i c a l C o a t i n g s f o r L a s e r A p p l i c a t i o n s , B u c h s , 9 t h j u n e 2 0 1 6

Lase r damage res i s tance o f op t i ca l coa t i ngs i n t he sub -ps reg ime : l im i t a t i ons

and imp rovemen t o f damage th resho ld

Laurent Gal la is*

A ix Marse i l le Univers i té , CNRS, Cent ra le Marse i l le , Ins t i tu t Fresnel UMR 7249, 13013 Marse i l le , France

* l a u r e n t . g a l l a i s @ f r e s n e l . f r w w w . f r e s n e l . f r / p e r s o / g a l l a i s


Topics: High performances optical interference filters Innovative concepts and components

Staff : 7 permanent, 2 PhD

Equipement : 250m² clean rooms 5 different machines with in situ optical monitoring: EBD, IAD, PIAD, DIBS, PARMS Commercial and custom characterization systems

Topics: Physics of laser material interactions (fs to CW) Laser damage of optical components for high power applications Laser processing

Staff : 6 permanent, 3 post-doc, 7 PhD students

Equipment : fs & ns LIDT measurements CW laser processing Commercial and custom characterization systems

Opt ica l Coat ing group Laser Mater ia l In teract ion group


I n t r oduc t i on Laser damage


I n t r oduc t i onLaser damage

High power laser

Costly optic



High power laser

Damage Initiation

10μm



High power laser

Damage Initiation

Local reduction of damage resistance

redu

10μm



High power laser

Damage Initiation


redu

Damage growth



High power laser

Damage Initiation


redu

Damage growth

contamination inatio



High power laser

Damage Initiation


redu

Damage growth


e



High power laser

Damage Initiation


redu

Damage growth


e

loss of integrity of the component

of inte



High power laser

Damage Initiation


redu

Damage growth


e


of inte

Beam obscuration

am



High power laser

Damage Initiation


redu

Damage growth


e


of inte

Beam obscuration

am

Scattering, reduction of R&T

S



High power laser

Damage Initiation


redu

Damage growth


e


of inte

Beam obscuration

am


Losses LS



High power laser

Damage Initiation


redu

Damage growth


e


of inte

Beam obscuration

am


Losses LS

Wavefront modulations Wm



High power laser

Damage Initiation


redu

Damage growth


e


of inte

Beam obscuration

am


Losses LS

Wavefront modulations

Degradation of beam quality

Wm

Db



High power laser

Damage Initiation


redu

Damage growth


e


of inte

Beam obscuration

am


Losses LS

Wavefront modulations

Degradation of beam quality

Wm

Db

Damage propagation prop

Other costly optic


Out l i ne

Basics of short pulse laser damage process Damage resistance of opt ical mater ia ls Defect- induced laser damage & damage growth Improvement of laser damage resistance


Out l i ne

Basics of short pulse laser damage process Damage resistance of opt ical mater ia ls Damage in i t iat ion on defects Improvement of laser damage resistance


Bas i cs o f sho r t pu l se l ase r damage p rocess Non- l inear ionizat ion

-4.0E-13 -2.0E-13 0.0 2.0E-13 4.0E-13

0

2E16

4E16

6E16

8E16

1E17

Inte

nsity

(W/m

²)

time (s)

1E14

1E17

1E20

1E23

1E26

1E29

Ele

ctro

n de

nsity

(m-3)

I on izat ion processes under h igh in tens i ty i l luminat ion

« f ree » e lect ron generat ion evolu t ion dur ing the pu lse

S c h e m a t i c r e p r e s en t a i o n o f Mu l t i -P h o t on I o n i za t i o n , Tu n n e l I o n i za t i o n , I m p a c t I o n i za t i o n a n d E l e c t r on i c Av a l a n c he

C a s e o f H f O 2 f i l m ( 5 . 5 e V) , a t 8 0 0 n m, 1 0 0 f s , 1 J / c m ²

Conduction band

Energy

Time

EV

Ec

Eg

PhotoionizationFree carrier-heating

Impact ionization& avalanche

MPI TI

Valence band


Bas i cs o f sho r t pu l se l ase r damage p rocessEnergy deposi t ion in the mater ia l

-1.0E-12 -5.0E-13 0.0 5.0E-13 1.0E-120.0

2.0E16

4.0E16

6.0E16

8.0E16

1.0E17

1.2E17 Intensity: Incident Reflected Transmitted Absorbed

Inte

nsity

(W.c

m-2)

Time (s)

Absorbed fluence

The mate r ia l becomes s t rong ly absorb ing due to f ree e lec t ron response

S ign i f i can t absorp t ion o f the lase r i n tens i t y occu rs due to op t i ca l p roper t i es evo lu t i on

E v o l u t i on o f t h e r e a l a n d i m a g i n a ry p a r t o f t h e r e f r a c t i v e i n d e x a s a f u n c t i on o f f r e e e l e c t r on d e n s i t y, a s d e s c r i b e d b y D r u d e m o d e l *

I n t en s i t y a s a f u n c t i on o f t i m e i n t h e c a s e o f a Ta 2O 5 f i l m i r r a d i a t ed w i t h a 5 0 0 f s , 1 0 3 0 n m p u l s e . *

1E14 1E17 1E20 1E23

1.4

1.6

1.8

2.0

2.2

2.4 Nb2O5

SiO2

refra

ctiv

e in

dex

n

Electronic density (cm-3)

0.0

0.2

0.4

0.6

0.8

1.0

extin

ctio

n co

effic

ient

k

*L. Gallais et al., Appl. Phys. Lett. 97, 051112 (2010)


Bas i cs o f sho r t pu l se l ase r damage p rocess

5.0 5.2 5.4 5.6 5.8 6.0 6.2 6.41

10

100

1000

10000

Abs

orbe

d en

ergy

per

mas

s un

it (J

/g)

Fluence (J/cm²)

Sc2O3 melting (Cp m)

Damage

Damage o f the mate r ia l t akes p lace when the depos i ted energy i s su f f i c ien t to cause mate r ia l mod i f i ca t i ons

Therma l o r mechan ica l p rocesses lead to ma te r ia l remova l

C a l c u l a t i on o f e n e r g y p e r u n i t o f m a s s d e p o s i t e d i n a S c 2O 3 f i l m w i t h 5 0 0 f s a t 1 0 3 0 n m *

H a f n i a f i l m s u b m i t t ed t o d i f f e ren t f l u e nc e s a t 5 0 0 f s / 1 030n m ( e a c h i m a g e i s a d i f f e ren t s i t e ) *

*D.B. Douti et al., Appl. Phys. A., to be published

Video not available in pdf version


Bas i cs o f sho r t pu l se l ase r damage p rocessTime scales

Bas ic processes occur a t d i f ferent t imescales: – Excitation

Absorption by free electrons in the material – Initial free electrons in metals – Free electrons created by non-linear ionisation in dielectrics

– Energy transfer From electrons to lattice Heat diffusion in the material

– Response of the material Phase change Hydrodynamic motion, shock waves Thermo-mechanical stress

– Material removal Thermal or mechanical effects depending on the deposited energy, material properties and irradiation conditions

time

fs

ps

ns

μs μ


Bas i cs o f sho r t pu l se l ase r damage p rocessMain di fferences wi th the ns regime

time

fs

ps

ns

μs μ

Laser / plasma

interaction will drive energy

deposition and

damage process

Energy deposition

and damage

processes are

separated in time

Main property: related to defects that can iniate a

plasma

Main property: related to intrinsic

properties of the material


Bas i cs o f sho r t pu l se l ase r damage p rocessMater ia l modi f icat ions under mul t ip le pulses Incuba t ion e f fec t re la ted to the

accumu la t ion o f e lec t ron ic de fec ts

Decrease o f the lase r damage res i s tance under mu l t i p le pu lses

T h e d i f f e re n t p a t h w a y s f o r e x c i t a t i on , r e l a x a t i on a n d t r a p p in g o f e l e c t r ons , c h a r a c t e r i ze d w i t h a r a t e / l i f e t i me

S i O 2 s i n g l e l a y e r, 5 0 0 f s , 1 0 3 0 n m , m u l t i p l e s h o t s a t 1 0 H z ( F l u e n c e s e t t o 7 0 % o f t h e s i n g l e p u l s e t h r e s h o ld )

Conduction Band

Valence Band

Defect levels

30μm



Bas i cs o f sho r t pu l se l ase r damage p rocess Thermal effects under mul t ip le pulses

1 10 100 1000 10000

0.25

0.50

0.75

1.00

1.25

1.50

Cal

cula

ted

LID

T (J

/cm

²)

Pulse number

Gold mirror: Silver mirror: 1kHz 4.3MHz

Sub-ps Laser i r rad ia t i on can loca l l y hea t the mate r ia l s

Hea t can accumu la te i f t he componen t does no t have t ime to coo l be tween two pu lses

F i n i t e - e l eme n t s i m u l a t i ons o f t h e t e m p era t u re r i s e o f a p r o t e c t ed g o l d m i r r o r 2μs a f t e r a 1 . 2 J f s , 8 0 0 n m , 1 0μm d i a m e t e r p u l s e *

F l u e n c e n e e d e d t o r e a c h t h e m e l t i ng p o i n t m e t a l l i c m i r r o r s a t 1 k H z a n d 4 . 3 MH z r e p e t i t i on r a t e s *

20°C

70°C

0 r (μm)

z (μm

)

65

0

-20

30 air

susbtrate

SiO2

Gold

*B. Nagy et al., Opt. Lett. 40, 2525 (2015)


Out l i ne



Damage res i s tance o f op t i ca l ma te r i a l s

0 2 4 6 8 10 120

1

2

3

4

5

AlF3

Al2O3

HfO2

Nb2O5

Sc2O3

SiO2

Ta2O5

TiO2

Y2O3

ZrO2

MgF2

CaF2 MgF2

CaF2LiF

Al2O3

SiO2

KBrNaCl

InfrasilBaF2

ZnSZnSe

GeSi

LIDT

(J/c

m²)

Bandgap (eV)

Ag, Pt

Thin films:

In t r insic Laser- Induced Damage Threshold

1.2 1.4 1.6 1.8 2.0 2.2 2.40

1

2

3

4

5 AlF3

Al2O3

Al2O3/AlF3

Al2O3/SiO2

HfO2

HfO2/SiO2

MgF2

Nb2O5

Nb2O5/SiO2

Sc2O3

SiO2

Ta2O5

Ta2O5/SiO2

TiO2

Y2O3

ZrO2

ZrO2/SiO2

LIDT

(J/c

m²)

Refractive index

D i rect dependence of L IDT on the mater ia l bandgap

Clear corre la t ion between the re f ract ive index and LIDT

L I D Ts o f o p t i c a l m a t e r i a l s t e s t e d i n s i n g l e - s h o t a t 5 0 0 f s a n d 1 0 3 0 n m a s a f u n c t i on o f t h e m e a s u red o p t i c a l b a n d g a ps *

L I D Ts o f o p t i c a l t h i n f i l m m a t e r i a l s a s a f u n c t i on o f r e f r a c t i v e i n d e x a t 1 0 3 0 nm * *

*L. Gallais et al., Appl. Opt. 53, A186 (2014) **B. Mangote et al., Opt. Lett. 37, 1478 (2012)



1E-13 1E-12 1E-11 1E-10 1E-9 1E-8

1

10

LID

T (J

/cm

²)

Pulse duration (s)

RLVIP EBD

Parametr ic dependence

1 2 3 40.0

0.5

1.0

1.5

2.0

LIDT

(J/c

m²)

Photon energy (eV)

Nb2O5 Simulation Ta2O5 Simulation HfO2 Simulation Al2O3 Simulation

L IDT decreases wi th pu lse durat ion for d ie lect r ics

L IDT decreases wi th wavelength

L I D T o f H f O 2 s i n g l e l a y e r c o a t i ngs m a d e b y R e a c t i v e L o w Vo l t a g e I o n P l a t i n g o r E l e c t r on B e a m D e p o s i t i on a s a f u n c t i on o f p u l s e d u r a t i on , t e s t ed a t 1 0 3 0 / 106 4nm *

L I D T a t 1 0 0 f s a s a f u n c t i on o f p h o t on e n e r g y f o r d i f f e ren t s i n g l e l a y e r c o a t i n gs * *

*L. Gallais et al., Appl. Opt. 50, C178 (2011) **L. Gallais et al., J. Appl. Phys. 117, 223103 (2015)



1 10 100 1000 10000 1000000

1

2

3

4

5

LID

T (J

/cm

²)

Number of pulses

1030nm 515nm 343nm

Mul t ip le pulses

1 10 100 1000 10000 1000000.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

LID

T (J

/cm

²)

Number of pulses

1030nm 515nm 343nm

Exc i ta t i ons o f m id -gap de fec t s ta tes a t the m ic roscop ic l eve l takes p lace under mu l t i p le i r rad ia t i ons , l ead ing to a dec rease o f L IDT w i th i nc reas ing pu lse number. Th is e f fec t i s s t rong ly dependen t on lase r i r rad ia t i on cond i t i ons and mate r ia l

E v o l u t i on o f t h e L I D T w i t h t h e n u m b e r o f p l u s e s a t 5 0 0 f s f o r S i l i c a f i l m d e p o s i t ed b y Ma g n e t r on S p u t t e r i n g *

E v o l u t i on o f t h e L I D T w i t h t h e n u m b e r o f p l u s e s a t 5 0 0 f s f o r N i o b i a f i l m d e p o s i t ed b y Ma g n e t r on S p u t t e r i n g *

*D.B. Douti et al., Opt. Eng. 53, 122509 (2014)


Damage res i s tance o f op t i ca l ma te r i a l sEnvironnemental condi t ions

LIDT decrease wi th pressure is observed for ox ides

No dependence wi th temperature is observed for cryogenic condi t ions

L I D T o f H a f n i a a n d S c a n d i a a t 1 0 3 0 nm , 5 0 0 f s , i n a i r a n d u n d e r v a c uu m ( 1 0 - 3m b a r ) *

L I D T ( 1 0 3 0 nm , 5 0 0 f s ) o f d i e l e c t r i c s m a t e r i a l s u n d e r v a c u u m a t d i f f e re n t t e m p e ra t u res *

*A. Hervy et al., Opt. Eng., to be published


Out l i ne



Sub-ps damage i n i t i a t i on on de fec t sPhysical process

Localized absorption of laser radiation

Energy transfer to host material

Mechanical & Hydrodynamic effects

-Free electron absorption -Photo-ionization -Electron dynamics -Non linear absorption -E-field distribution effects

-electron/phonon relaxation thermal conduction and radiation -plasma ball formation -avalanche ionization -melting, vaporisation -laser driven absorption

-high internal pressure, -thermomechanical stress -shock wave -spalliation -fragmentation -ejection

Small precursors can initiate a cascade of events that can result in a macroscopic damage

time fs ps ns μs

Sub-ps pulse

ns pulse


Sub-ps damage i n i t i a t i on on de fec t s Defect in i t iat ion

Macroscop ic de fec ts can induce s t rong l oca l i n tens i t y enhancement

Loca l reduc t ion o f damage th resho ld i s observed on nodu la r de fec ts

F D T D s i m u l a t i on s o f | E | ² d i s t r i bu t i ons f o r a n o d u l a r d e f e c t i n a H f O 2/ S i O 2 H R m i r r o r *

D a m a g e i n i t i a t ed b y a n o d u l a r d e f e c t s o n a H R m i r r o r u n d e r s u c c es s i v e i r r a d i a t i ons a t 1 . 4 5 J 2. *

10μm

0 1 2

5 10 50

*L. Gallais et al., Opt. Lett. 39, 1545 (2014)


Sub-ps damage i n i t i a t i on on de fec t sDamage densi t ies

Spec i f i c damage tes t p rocedures can be app l ied to quan t i l f y l im i t i ng de fec ts (damage dens i t i es / f l uence)

I so la ted damage even ts re la ted to de fec ts can occur fo r f l uences s ign i f i can t l y l ower than the “ i n t r i ns i c ” L IDT

S c h e m a t i c d e s c r i p t i on o f a R a s t e r s c a n t e s t

D a m a g e s i t e s r e v e a l ed b y a R a s t e r s c a n t e s t o n a H R MML D m i r r o r ( 1 0 3 0nm , 1 p s )

4mm

1on1 LIDT 0.8J/cm² Raster scan

100 damages/cm² @0.4J/cm²


Sub-ps damage i n i t i a t i on on de fec t sDamage growth

Once damage s i te i s i n i t i a ted , ca tas t roph ic damage g rowth l im i t s the op t i cs l i f e t ime

Growth can be t r i ggered fo r f l uences as low as 50% o f the in t r i ns i c damage th resho ld o f the componen t .

S e q u e nc e o f s h o t s o n a d e f e c t -i n i t i a t ed d a m a g e , a t a f l u e n c e s e t t o 6 0 % o f t h e s i n g l e p u l s e L I D T *

E v o l u t i on o f t h e p r o b a b i l i t y o f g r o w t h a s a f u n c t i o n o f f l u e n c e ( n o r ma l i ze d w i t h r e s p ec t t o t h e s i ng le p u l s e L I DT ) . HR m i r r o r, 45 ° , P, 1 0 3 0 n m, 1 p s . *

20μm

*M. Sozet et al., Opt. Lett. 41, 2342 (2016)



Out l i ne

Basics of short pulse laser damage process Damage resistance of opt ical mater ia ls Damage in i t iat ion on defects Improvement of laser damage resistance?


Imp rovemen t o f l ase r damage res i s tance

1.2 1.4 1.6 1.8 2.0 2.2 2.40

1

2

3

4

5 AlF3

Al2O3

Al2O3/AlF3

Al2O3/SiO2

HfO2

HfO2/SiO2

MgF2

Nb2O5

Nb2O5/SiO2

Sc2O3

SiO2

Ta2O5

Ta2O5/SiO2

TiO2

Y2O3

ZrO2

ZrO2/SiO2

LIDT

(J/c

m²)

Refractive index

Mater ia ls & manufactur ing

Eng ineered mate r ia l s such as b ina ry m ix tu res a re i n te res t ing comb ina t ions fo r i n te r fe rence coa t ings used in h igh -power app l i ca t ions

Reduc t ion o f de fec t dens i t i es re la ted to the manu fac tu r ing p rocess

L I D T o f I B S S c 2O 3/ S i O 2 m i x t u re s c o m p are d t o o t h e r c o a t i ng m a t e r i a l s *

R a s t e r s c a n a n d 1 o n 1 m e a s u re men t s o n d i f f e r en t H R m i r r o r s ( 1 0 5 3 n m, 67 5 f s , 45 ° AOI , P po la r ) *

*M. Mende et al., Appl. Opt. 52, 1368 (2013) *M. Sozet et al., Opt. Lett. 40, 2091 (2015)


Imp rovemen t o f l ase r damage res i s tanceOpt imizat ion of E-f ie ld distr ibut ion

The theore t i ca l L IDT o f a componen t can be ob ta ined f rom the knowledge o f the E- f i e ld d i s t r i bu t ion and L IDT o f ma te r ia l s

S ign i f i can t improvement can be ob ta ined w i th op t im iza t ion o f the E- f i e ld d i s t r i bu t ion

O pt i m i za t i on o f 45 ° b r oadb and HR-c o a t i ng s . f o r A p p o l o n 1 0 P W l a s e r p r o j e c t *

L I D T o f b r o a d ba nd r e f l e c t i v e m i r r o r s : R > 9 9 % , > 2 5 0 nm ( S ) / 1 6 0 n m ( P ) Te s t s a t 8 0 0 n m , 4 0 f s , 5 k H z* *

LIDT

(J/c

m²)

Standard (commercial samples) ( p ) Optimized p

0

2

/4 T

iO2/

SiO

2

*A. Hervy et al., Opt. Eng., to be published **A. Hervy, PhD thesis, 2016


Imp rovemen t o f l ase r damage res i s tance Post processing

Laser cond i t i on ing o r the rma l annea l ing can s ign i f i can t l y enhance the L IDT

Spec i f i c t rea tmen ts can m i t i ga te (a r res t ) l ase r damage g rowth

I m p r ov em en t o f L I D T o n t h e s u r f a c e o f f u s e d s i l i c a o p t i s a t 3 5 5 n m, 3 n s , w i t h i s o t h e rm a l an nea l i ng a t 105 0°C f o r 12h *

E x a m p l e o f C O 2 l a s e r p r o c e s s i ng o f d a m a g e o n f u s e d s i l i c a f o r t h e L a s e r Me g a J o u le p r o j e c t *

*T. Doualle et al., J. Appl. Phys. 119, 213106 (2016) *T. Doualle et al., Submitted

2mm



Conc lus ions

The phys ics o f laser damage in the sub-p icosecond reg ime is qu i te wel l understood

In t r ins ic per formances of opt ica l mater ia ls can be ranked based on the i r bandgap and sca l ing laws can be der ived

Consequent ly theoret ica l ly h igh laser damage threshold opt ics can be des igned based on avai lab le mater ia ls

However for appl icat ions two main po in ts need to be cons idered and deeply s tud ied:

‘Incubation’, ‘fatigue’ or heat accumulation effects of the materials under multiple pulses The densities of growing damage sites related to manufacturing defects and/or contamination

Post process ing techniques that have been appl ied in the ns reg ime (anneal ing, laser condi t ion ing, damage growth mi t igat ion,etc . . ) cou ld a lso be of potent ia l in terest


Thank you fo r you r a t t en t i on !Acknowledgments

Laser Material Interactions group Optical Coating group

CESTA/Laser Damage group, PETAL project, LMJ project

Laser Research Center / Laser Damage group

Laser Components Department

Apollon project Coating department

Laser damage resistance of optical coatings in the sub-ps regime ... · Optical Coatings for Laser...

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