SIMULATION OF DOUBLE-PULSE LASER ABLATION OF METALS

Transcription

1 SIMULATION OF DOUBLE-PULSE LASER ABLATION OF METALS M. Povarnitsyn, K. Khishchenko, P. Levashov Joint Institute for High Temperatures, RAS, Moscow, Russia T. Itina Laboratoire Hubert Curien, CNRS, St-Etienne, France Workshop on the Modeling and Ultra-Fast Laser Processing Carry le Rouet, France March 19, 2010

2 Outline Motivation Set-up configuration Double pulse experiments Numerical model Basic equations Transport properties Equation of state Fragmentation effects Results of modeling Summary 2

3 LIBS application Industrial applications Pharmaceutical analysis Advantages 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 multielemental 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). Disadvantages 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. Planetary science 3

4 Double-pulse technique Plasma luminosity higher with the double pulse A. Semerok, CEA 4

5 Double pulse set-up 2 x 2 J/cm 2 Ti:Sapphire λ=800 nm FWHM = 100 fs 5

6 Experiment: single & double pulses, Cu double pulse single pulse A.Semerok & C. Dutouquet Thin Solid Films (2004) 6

7 Experiment: single & double pulses J. Hermann & S. Noël, LP3 (PhD 2008) T. Donnelly et al. J. Appl. Phys. 106,

8 Two-temperature multi-material Eulerian hydrodynamics Basic equations Mixture model 8

9 Transport properties on melting K. Eidmann et al. Phys. Rev. E 62, 1202 (2000) Handbook of optical constants of solids, E. Palik et al. 9

10 Pump-probe technique Reflectivity R Phase shift ψ M.B. Agranat et al. JETP Letters, 85, #6, (2007) Physical model

11 Two-temperature semi-empirical EOS Al Temperature, kk 10 1 g (g) unstable l+g CP sp bn (l) l s+l 10 1 s+g (s+l) (s) s Density, g/cm 3 11

12 Mechanical spallation (cavitation) Temperature, kk 10 1 (g) g l+g unstable s+g CP (s+l) (l) Density, g/cm 3 l (s) P = 0 GPa P = -2 GPa P = -5 GPa s+l s 10 1 P P P liquid + voids Time to fracture is governed by the confluence of voids 12

13 Spallation criteria Strain rate in laser experiments is up to s -1 Energy minimization D. Grady, J. Mech. Phys. Solids 36, 353 (1988). 13

14 Basic features of the model 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) 14

15 Simulation: single pulse 15

16 Simulation: x-t diagram of Cu, F=1.2 J/cm 2 phase states laser pulse new surface density initial surface 16

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). M.E. Povarnitsyn et al., Proc. SPIE 7005, (2008) 17

18 Simulation: double pulse with τ delay =50ps 18

19 Simulation: delay 50 ps, density of Cu 2nd pulse 2 d pulse 1st pulse 1 st pulse 19

20 Simulation: delay 50 ps, phase states of Cu (g) 2nd pulse (l) 2 d pulse 1 st pulse g l+g l s 1st pulse 20

21 x-t diagram of phase states according to EOS 21

22 Simulation: single & double pulse 2 2 J/cm 2 Povarnitsyn et al. PRL 103, (2009) 22

23 Summary Model describes ablation depth for single and double pulse experiments in the range J/cm 2. 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. 23