Shock, ablation and formation of nanostructures in metals induced by femtosecond laser

S.I. Ashitkov, P.S.Komarov, N.A. Inogamov, V.V. Zhakhovsky, M.B. Agranat, G.I. Kanel

Joint Institute for High TemperaturesRussian Academy of Sciences, MoscowJIHT of RAS

Santa Fe, NM, USA, April 21-25, 2014

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MOTIVATION

Laser matter interaction/ experiment and modeling

Materials behavior near the theoretical limit of shear and bulk strength

Development of a theory of plasticity and fracture

Femtosecond laser surface nanostructuring

OUTLINE

Shock compression of aluminum and iron in picosecond range.- - super elastic shock waves at submicron scale - - achievement of ultimate values of the shear and bulk strength -- - possibility of α→ε polymorphic phase transition in iron

Frontal ablation and rear side spallation of aluminum.

Formation of nanostructures: MD simulations and experiment

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Shock compression of metals. Appearance of material properties in a free surface history. Shock wave structure.

Diagnostics of shock phenomena areperformed by measuring a free surfacevelocity profile of a tested sample.Free surface velocity history

In plate impact experiment*.

*G.I. Kanel', V. E. Fortov,S.V. Razorenov Physics-Uspekhi 50, (8) (2007)

Time t, µs

Free

Sur

face

Vel

ocity

ufs

, km

/s

13 GPa

∆ufs

Armco-iron2.46 mm

α→ε polymorphic phase transition in iron: (bcc → hcp crystal structure transition)Transition stress ≈13GPa in a microsecond range

Reflection of shock compression pulse from thefree surface leads to appearance of the tensile stresses inside of the sample causing fracture.Value of spall strength is determined from:

2/0efs

eSHEL uU ∆= ρσ

Splitting of shock wave into elastic precursor (HEL) andplastic compression wave makes it possible todetermine the plasticflow stress of the material.

2/)(0 δρσ +∆= fsSspall uU

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Ultrafast Chirped Pulse Interferometry

00.511.52.02.5

0 200

0

100

200

Time, ps

Posi

tion

y, µ

m

Phase shift, rad

100

-Detected range 0 ÷ 240 ps-Temporal resolution 1ps-Lateral spatial resolution 2 µm-Displacement accuracy 1÷2 nm-Measurements in a single shot

Amplifier CompressоrStretcherOscillator

Probe 300 ps8 0 1 0 0 1 2 0 1 4 0 1 6 0 1 8 0 2 0 0

- 1 , 0

- 0 , 5

0 , 0

0 , 5

1 , 0

C

A

Sample

CCD

Pump 100 fs

ImagingSpectrometerActon 2300i

ImagingMichelson

interferometr

Femtosecond Ti:S laser (Legend, Coherent, USA)

Time t, ps

790810 770

0 80 160 240

Probe wavelength, nm

Time t, ps

790810 770

0 80 160 240

Probe wavelength, nm

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In contrast to multipulse pump–probemethods the single-pulse techniqueensures much higherreliability of themeasurements and can be used toanalyze the reproducibility and statisticsof shock wave phenomena in thin filmsamples.

Application of Fourier processing ofinterference patterns and comparison of phase distributions obtained before and during shock wave arrival ensure measurement of surface displacement

with nanometric accuracy.

2D Fourier processing of interference patterns

Spatial-temporal phase distribution

Time and spatial resolved diagnostics of a rear surface displacement

Samples: metallic films, deposited by magnetron spattering onto glass substrates of 150 µm in thick

),( tyϕ∆Phase distributions at the rearsurface of iron targets of different thicknesses after shock breakout

d1

d2

pump100 fs

chirped probe300 ps

80 100120140160180200

-

-0,5

0,5

1

C

Ti:S laser

Glass substrate

Metal film

Gaussian spot Ø=40 µm

Phas

e shif

t, rad

2000 100

0.51

1.52

0

0.51

1.52

0250

0

200150

50100

250

0

200150

50100

Time t, ps

Posit

ion y,

a.u.

Fe, 250 nm

Fe, 540 nm

0 50 100 150 200 250

0

50

100

150

Dis

plac

emen

t, nm

Time t, ps

Al 500 nm

1200 nm

Free surface displacement histories πϕλ 4/),()(),( tyttyz ∆=∆

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Elastic-plastic shock wave in iron

0 50 100 150 2000,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

540 nmFe Shot # 8

Free

Sur

face

Vel

ocity

, km

/s

Time, ps

HEL

PSW

Splitting of shock into elastic-plastic two-wave configuration at propagation distance of 540 nm

Free surface displacement and velocity history at different stressTi:S laser: 100fs, 3 J/cm

0 50 100 150 200

0

20

40

60

80

100

Dis

plac

emen

t z, n

m

Time t, ps

Fe, Shot#8540 nm

Sample: 99.9 purity iron film 540 nm in thickdeposited on glass substrate

Evolution of laser driven shock waves in Al and Fe at a submicron scale. Elastic Hugoniout

0 50 100 150 200 2500,0

0,4

0,8

1,2

1,6

2,0

Fre

e Su

rface

Vel

ocity

, km

/s

Time, ps

500 nm

1200 nm

Al, 3J/cm2

7.1 km/s

8 GPa

14 GPa

50 100 150 2000,0

0,5

1,0

1,5

2,0

Fe, 3 J/cm2

250 nm

540 nm

Free

Sur

face

Vel

ocity

, km

/s

Time, ps

6.4 km/s

HEL

HEL27 GPa

13 GPa

Free surface velocity histories

0,00 0,25 0,50 0,75 1,005

6

7

8

US = 5.35 + 1.34 up

USE = 6.44 + 1.4 up

US,

km

/s

up, km/s

- In iron splitting of shock wave into two-zone elastic-plastic configuration was observed- In aluminum pure elastic wavewas detected at stress up to 14 GPawith parameters rise time of 1-2 ps

US – up diagrams. Elastic Hugoniout.

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P – V diagrams. Shear strength of aluminum and iron

7.5 GPaup to 7.9 GPaFe

3.4 GPaup to 3.2 GPaAl

Theoretical limitExperimental value

))()((43 VpVz −= στ

Recorded states in elastic shock waves (points) in aluminum and iron films

Maximum shear stress at uniaxial compression:

))()((43 VpVz −= στ

0,80 0,85 0,90 0,95 1,000

5

10

15

20

σz - p = 2.4 GPa τ = 1.8 GPa

Bulk:US = 5.35 + 1.34 up

Elastic: US = 6.44 + 1.4 up

σ, G

Pa

V/V0

σz - p = 4.3 GPa τ = 3.2 GPa

Al

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Decay of the elastic precursor in aluminum and iron

S.I. Ashitkov, et al JETP Lett. 98, 384(2013)J.C.Crowhurst, et al J.Appl. Phys. 115, 113506 (2014)

10-3 10-2 10-1 100 1010,01

0,1

1

10

Al, HELWhitley, et al

Gupta, et al

Ashitkov, et al

Garkushin, et al

Arvidsson, et al

Winey, et alσ HEL

, GPa

Distance h, mm

Crowhurst, et al

083.002

45.001 )()( −− += hhShhSHELσ63.0

0 )( −= hhSHELσ

Smith et al

Kanel et al

Ashitkov et al

Crowhurst et al

S.I.Ashitkov, et al JETP. Lett. 92, 516 (2010)V. H. Whitley, et al J.Appl. Phys. 109, 013505 (2011)J.C.Crowhurst, et al Phys.Rew.Lett. 107, 144302 (2011)

- Super elastic shock waves with the stress >10 GPa were detected at submicron propagation distance- Decay of the elastic precursor is connected with plastic strain rate :

l

px

cG

dhd γσ &

34

HEL

−=pγ&

(G - shear modulus )

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The α→ ε phase transition in iron at strain rate ~109 s-1

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Fe, 0.5 µm

Laser, 100 fs

t

Px

Glass

50 ps

Sample: Fe film on a glass substrate

Fe

- HEL = 13-14 GPa at propagation distance 0.54 µm- deviatoric stress 4.5 GPa- PSW stress is up to 23GPa- observation of a trend to splitting PSW into two waves- but α→ε polymorphic transition in ironisn’t realized within 20 ps

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LLNL Livermore, 2013

Fe

- HEL = 10-12 GPa at propagation distance 1.2-1.6 µm- deviatoric stress exceeds 3 GPa- transition stress is up to 25GPa- α→ε polymorphic transition in ironis realized within 100 ps

J.C. Crowhurst et al, J.Appl. Phys. 115, 113506 (2014)

Fe, >1µmLaser, 300 ps

t

Px

Glass

300 ps

Sample: Fe film on a glass substrate

Fe

1.6 µm

1.2 µm

100 ps

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Spall strength of aluminum and iron at strain rate ~ 108 - 109 s-1

2

fsfslspall uubc ∆∆−= )2(21

0ρσ

cuVV fs 2/ 0 && =

S.I.Ashitkov, et al JETP. Lett. 92, 516 (2010)

nonlinearity of compressibilityStrain rate

Ideal strength 28 GPa

0 50 100 150 200 2500

50

100

150

0,0

0,5

1,0

1,5760 nmAl

1200 nm

Dis

plac

emen

t z, n

m

Time, ps

F=2J/cm2

∆ufs

Fre

e Su

rface

Vel

ocity

, km

/s

∆ufs

Free surface velocity historiesindicate spallation at a pure elastic uniaxial compression

in a picosecond range

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2N.A. Inogamov, et al Contr.Plasma Phys. 53, 796 (2013)

(a) - density map (b-e) - atomic order map: solid (green), liquid (red)

Expansion of foam,breaking ofmembranes, and freezing theremnants of membranes nearthe transit between foam andcontinuous metal.

Result of long large-scale MD simulation of a sample withdimensionsLxLyLz = 500x240x24 nm3

and 172x106 atoms.Laser: 100 fs; F/F abl =1.5

SEM images of ablation crater at a surface of gold sample.Laser: 100 fs; F/Fabl=1.5

Formation of nanostructures on metal surface afterfemtosecond laser irradiance above ablation threshold

15 µm1.5 µm

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Dynamics of surface layer expansion during femtosecond ablation of aluminum

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chirped probe300 ps

80 100120140160180200

-

-0,5

Glass substrate

Al film760 nm

Ti:S laserpump100 fsGaussian

spot Ø=40 µmF0 = 0.9 J/cm2

0

0.1

0.2

0.3

Phas

e sh

ift, r

ad

x, a.u.Time, ps 0

120

Temporal spatial phase distribution

80 100 120 140 160 180

0

5

10

15

20

Dis

plac

emen

t z, n

m

Time t, ps

F/ Fa=1.2

F/ Fa=0.9

F/ Fa=0.7

Al

40 n

m

Crater

50 µmProfile of ablation crater

Displacement history

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Ablation threshold 0.7 J/cm2

Frontal and rear side spallation in aluminum

500 1000 1500 2000 2500 30004

6

8

10

12

14

16

ρ c

10

5 , gc

m-2

c-1

T, K

Tm=933 K

AlSolid

Liquid

452.5±0.53· 1093.62.16Liquid (2kK)2507.7±0.52· 1096.42.71Solid (300 K)

LSpall, nmσSpall,, GPa, s-1c, km/sρ, gccAl

2/)( maxmin ttcLspall −=

Map of local atomic order

Frontal and rear surface velocity history

experimentMD

2/ucspall ∆= ρσ

Frontal surface Rear surface

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ε&

cu fs 2&& =ε

0 50 100 150

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

∆u=0.65km/s

Sur

face

Vel

ocity

u, k

m/s

Time t, ps

Rear Surface

Al, 760nm

Frontal Surface

∆u=1 km/s

F=2.1 J/cm2

F=0.9 J/cm2

Ti:S laser, 100 fs

*

* N.A.Inogamov et al JETP Lett 91 (2010)

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SUMMARY

Single shot interferometric diagnostics was realized to measure surface displacement history with temporal resolution of 1 ps.

Experimentally found that uniaxial shock compression in picosecond range is elastic up to stress of 14 GPa in aluminum and 27 GPa in iron.

The stressed states in aluminum and iron, very close to the values of ultimate shear and bulk strength were measured and implemented in picosecond range of load duration

The α→ε polymorphic phase transition in iron film of 540 nm in thick isn’t realized at a stress of 23 GPa within 20 ps after HEL

From the expansion surface history the value of tensile stress of about 2.5 GPa leads to spallation of liquid layer of aluminum just above the ablation threshold under femtosecond heating was measured.

The results of long large-scale MD simulations of nanostructures formation at metal surface after it’s irradiance of femtosecond laser is well similar to SEM images of ablation crater’s morphology

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Thank you for yourattention!