SIMULATION 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

Workshop on the Modeling and Ultra-Fast Laser ProcessingCarry le Rouet, France

March 19, 2010

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

— Basic equations— Transport properties— Equation of state— Fragmentation effects

• Results of modeling• Summary

Outline

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LIBS application

•Increased cost and system complexity.

•Large interference effects (including matrix interference and, in the case of LIBS in aerosols, the potential interference of particle size).

•Detection limits are generally not as good as established solution techniques.

•Poor precision - typically 5-10%, depending on the sample homogeneity, sample matrix, and excitation properties of the laser.

•Versatile sampling of solids, gases or liquids.

•Little or no sample preparation is necessary.

•LIBS typically samples very small amounts of material and is non-destructive.

•Permits analysis of extremely hard materials.

•Possibility of simultaneous multi-elemental analysis.

•Potential for direct detection in aerosols (a solid or liquid particle in a gaseous medium).

•Simple and rapid analysis (ablation and excitation processes are carried out in a single step).

DisadvantagesAdvantages

Planetary science

Pharmaceutical analysis

Industrial applications

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Double-pulse technique

A. Semerok, CEA

Plasma luminosity higher with the double pulse

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Ti:Sapphire

Double pulse set-up

λ=800 nmFWHM = 100 fs

2 x 2 J/cm 2

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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 (PhD 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)

Pump -probe technique

M.B. Agranat et al. JETP Letters, 85, #6, (2007)

Reflectivity RPhase shift ψ

Physical model

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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)

Tem

pera

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)

Tem

pera

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 (ν, ε, χ)

• 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/cm 2

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 ττττdelay=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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x-t diagram of phase states according to EOS

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Simulation: single & double pulse 2 ×××× 2 J/cm 2

Povarnitsyn et al. PRL 103, 195002 (2009)

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