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ON THE MODELING OF DOUBLE PULSE LASER ABLATION OF METALS

M. Povarnitsyn, K. Khishchenko, P. LevashovJoint Institute for High Temperatures, RAS, Moscow, Russia

povar@ihed.ras.ru

T. ItinaLaboratoire Hubert Curien, CNRS, St-Etienne, France

XIII International Conference on Physics of Non-Ideal PlasmasChernogolovka, Russia

September 16, 2009

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• Motivation• Set-up configuration• Double pulse experiments• Numerical model

— Basic equations

— Transport properties

— Equation of state

— Fragmentation effects• Preliminary results• Summary

Outline

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Ti:Sapphire

Double pulse set-up

=0.8 mkmFWHM = 100 fs

2 x 2 J/cm2

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Experiment: single & double pulses, Cu

A.Semerok & C. Dutouquet Thin Solid Films 453 – 454 (2004)

double pulse

single pulse

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Experiment: single & double pulses

J. Hermann & S. Noël, LP3 (2008) T. Donnelly et al. J. Appl. Phys. 106, 013304 2009

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Two-temperature multi-materialEulerian hydrodynamics

Basic equations Mixture model

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Transport properties

Handbook of optical constants of solids, E. Palik et al.

on melting

K. Eidmann et al. Phys. Rev. E 62, 1202 (2000)

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Two-temperature semi-empirical EOS

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

bnunstable

sp

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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

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

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Spallation criteria

D. Grady, J. Mech. Phys. Solids 36, 353 (1988).

Energy minimization

Strain rate in laser experiments is up to 1010 s-1

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• Multi-material hydrodynamics (several substances + phase transitions)

• Two-temperature model (Te Ti)

• Two-temperature equations of state

• Wide-range models of el-ion collisions, permittivity, heat conductivity (, , )

• Model of laser energy absorption (Helmholtz)

• Model of ionization & recombination (metals)

Basic features of the model

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Simulation: single pulse

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phase states

Simulation: x-t diagram of Cu, F=1.2 J/cm2

density

laser pulse

new surface

initial surface

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Ablation depth vs. fluence

Experiment:

M. Hashida et al. SPIE Proc. 4423, 178 (2001).

J. Hermann et al. Laser Physics 18(4), 374 (2008).

M.E. Povarnitsyn et al., Proc. SPIE 7005, 700508 (2008)

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Simulation: double pulse with delay=50ps

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Simulation: delay 50 ps, density of Cu

1st pulse

2d pulse

1st pulse

2nd pulse

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Simulation: delay 50 ps, phase states of Cu

1st pulse

2d pulse

l+g

g

(g)

s

(l)

l1st pulse

2nd pulse

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Simulation: single & double pulse 22 J/cm2

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Summary

• Model describes ablation depth for single and double pulse experiments in the range 0.1 – 10 J/cm2.

• For long delays the second pulse interacts with the nascent ablation plume (in liquid phase).

• Reheating of the nascent ablation plume results in suppression of the rarefaction wave.

• Back deposition of substance caused buy the second

pulse is the reason of even less crater depth for double pulses with long delay.