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Transcript of 1 Phase transitions in femtosecond laser ablation M. Povarnitsyn, K. Khishchenko, P. Levashov Joint...
1
Phase transitions in femtosecond laser ablation
M. Povarnitsyn, K. Khishchenko, P. Levashov
Joint Institute for High Temperatures RAS, Moscow, [email protected]
E-MRS 2008 Spring MeetingStrasbourg, France
27 May, 2008
2
1. Introduction
2. Setup parameters
3. Mechanisms of ultrashort laser ablation
4. Numerical model• Basic equations• Equation of state (EOS)• Thermal decomposition model (homogeneous nucleation)• Mechanical decomposition model (cavitation)
5. Results• Dynamics of ablation• Analysis of phase states• Sensitivity to EOS
6. Conclusions and future plans
Outline
3
Setup parameters
laser
targets: Al, Au, Cu, Ni = 0.8 mkm,L = 100 fs, ( FWHM )F = 0.110 J/cm2
Single pulse, Gaussian profile
Actual questions:
• Heat affected zone (melted zone)• Shock wave formation• Parameters of the plume• Cavitation and fragmentation• Generation of nanoclusters• Ablation depth vs. laser fluence
4
Stages of ultrashort ablation
t = 01. Pulse L ~ 100 fs
~10 nm
t < 1 ps
2. Energy absorption by conduction band electrons
~100 nm
t ~ 5 ps
3. Heat conductivity + electron-lattice collisions
t > 10 ps
4. Thermal decomposition and SW and RW generation
t ~ 100 ps
5. Mechanical fragmentation
V > 10 km/s
V ~ 1 km/s
V < 1 km/s
SWRW
RW
5
Two-temperature multi-materialEulerian hydrodynamics
Basic equations Mixture model
6
Two-temperature semi-empirical EOS
“Stable” EOS
1
10
1
10
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
Density, g/cm3
Al
l+g
Te
mp
era
ture
, kK
s
lg
s+g
s+l
CP
kinetic models
1
10
1
10
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
Density, g/cm3
l+g
(s)
(g)
(s+l)
(l)
Te
mp
era
ture
, kK
Al
s
lg
s+g
s+l
CP
sp
bnbn
unstable
bn
“Metastable” EOS
7
1
10
1
10
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
Density, g/cm3
l+g
(s)
(g)
(s+l)
(l)
Te
mp
era
ture
, kK
Al
s
lg
s+g
s+l
CP
Thermal decomposition of metastable liquid
Metastable liquid separation into liquid-gas mixture
dP/dt = -(P-Peq)/M
dT/dt = -(T-Teq)/T
unstable
8
Model of homogeneous nucleation
V.P. Skripov, Metastable Liquids (New York: Wiley, 1974).
1
10
1
10
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
Density, g/cm3
l+g
(s)
(g)
(s+l)
(l)
Te
mp
era
ture
, kK
Al
s
lg
s+g
s+l
CP
0.9Tc<T<Tc
unstable
9
1
10
1
10
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
Density, g/cm3
P = 0 GPa P = -2 GPa P = -5 GPa
l+g
(s)
(g)
(s+l)
(l)
Te
mp
era
ture
, kK
s
lg
s+g
s+l
CP
Mechanical spallation (cavitation)
P
P
P
Time to fracture is governed by the confluence of voids
liquid + voidsunstable
10
Spallation criteria
Minimal possible pressure
D. Grady, J. Mech. Phys. Solids 36, 353 (1988).
P < -Y0
Energy minimization
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Dynamics of ablation of Al target
0
10
20
30
40
50
0
10
20
30
40-200 0 200 400 600
0
1
2
3
4D
ensi
ty (
g/cm
3 )
10 ps
-200 0 200 400 600
20 ps
-200 0 200 400 600
0
1
2
3
4
x (nm)
Den
sity
(g/
cm3 )
30 ps
-200 0 200 400 600
x (nm)
80 ps
Pre
ssur
e (G
Pa)
Pre
ssur
e (G
Pa)
TM
P
P
P
P
F = 5 J/cm2
M. E. Povarnitsyn et al. Phys. Rev. B 75, 235414 (2007).
12
Results with “stable” and “metastable” EOS
1
10
1
10
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
Density, g/cm3
Al
l+g
Te
mp
era
ture
, kK
s
lg
s+g
s+l
CP
1
10
1
10
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
Density, g/cm3
l+g
(s)
(g)
(s+l)
(l)
Te
mp
era
ture
, kK
Al
s
lg
s+g
s+l
CP
SW
P ~ 0
P ~ Pmin<0
SW
P ~ 0
(l)
unstable
F = 5 J/cm2
13
Ablation of Al target
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Ablation of Au target
15
Ablation of Cu target
16
Ablation of Ni target
17
Ablation depth vs. fluence
Experiment:
M. Hashida et al. SPIE Proc. 4423, 178 (2001).
J. Hermann et al. Laser Physics 18(4), 374 (2008).
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1
10
1
10
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
Density, g/cm3
Al
l+g
Te
mp
era
ture
, kK
s
lg
s+g
s+l
CP
1
10
1
10
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
Density, g/cm3
l+g
(s)
(g)
(s+l)
(l)
Te
mp
era
ture
, kK
Al
s
lg
s+g
s+l
CP
Mechanisms of ablation
Y. Hirayama, M. Obara Appl. Surf. Science 197-198 (2002)
unstable
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Conclusions and outlook
1. Simulation results are sensitive to the models used: absorption, thermal conductivity, electron-lattice collisions, kinetics of nucleation, fragmentation criteria, EOS, etc…
2. Time-dependent criteria of phase explosion and cavitation in metastable liquid state were introduced into hydrodynamic model
3. Usage of “metastable” and “stable” EOS allows to take into account kinetics of metastable liquid decomposition
4. Observed mechanisms of ablation:• thermal decomposition in the vicinity of critical point• cavitation in liquid phase at high strain rate and negative pressure
5. Ablation depth correlates with the melted depth
6. Kinetics of melting is in sight