Designer pulses for optimal ablation: guiding heat in ultrafast laser ablation plasmas

Abstract : The possibility of choosing thermodynamic trajectories for the excited matter is a determinant factor for controlling a typical laser ablation process, particularly when we approach irradiation on ultrafast timescales. This specifically concerns the nature and the energetic characteristics of the ablation products subsequent to laser irradiation. In this respect, designing the energy delivery rate using programmable pulse shaping methods in the temporal domain is a powerful way for controlling excitation and thermodynamic relaxation of the material and, equally, its hydrodynamic advance. We focus here on ultrafast laser irradiation of metals, with the objective of maximizing heat load in the ablation products. Using experimental and theoretical adaptive loops [1,2] based on hydrodynamic codes we indicate the shapes of optimal pulses on ultrashort and short timescales required to reach extreme thermodynamic states at limited energy input. These waveforms, particularly impulsive pulses on picoseconds pedestals, affect the excitation level and the energetic content of the ablation products, as well as the balance between thermal and mechanical energy. As the material states rapidly vary from solid to plasma phases, the optimal interaction scenario usually imply light coupling into the incipient material hydrodynamic motion. This triggers transitions to weakly-coupled front plasmas at critical optical density favoring energy confinement with low mechanical work. Additional collisional heating occurs in denser regions above the critical point, reaching states that spontaneously decompose in excited atomic species. The consequences are manifold and are particularly visible in the formation of atomic, ionic, and cluster species, their kinetics and spectral emissivities, and in the ejection of nanoscale liquid droplets. A discussion on the nature of these resulting exotic thermodynamic states, mostly implying supercritical paths, will be given. The results are interesting for remote spectroscopy applications, e.g. LIBS and secondary sources, ablation process quality, and for the laser-assisted generation of nanoparticles and PLD. References: 1. J.P. Colombier, P. Combis, A. Rosenfeld, I.V. Hertel, E. Audouard, R. Stoian "Optimized energy coupling at ultrafast laser irradiated metal surfaces by tailoring intensity envelopes. Consequences for material removal from Al samples" Phys. Rev. B 74, 224106/1-16 (2006) 2. Guillermin, J.P. Colombier, S. Valette, E. Audouard, F. Garrelie, R. Stoian, "Optical emission and nanoparticle generation in Al plasmas using ultrashort laser pulses temporally optimized by real-time spectroscopic feedback" Phys. Rev. B 82, 035430/1-16 (2010)
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Advanced Laser Technologies, Sep 2011, Golden Sands, Bulgaria
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Contributeur : Razvan Stoian <>
Soumis le : mercredi 7 mars 2012 - 21:11:34
Dernière modification le : mercredi 25 juillet 2018 - 14:05:31

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  • HAL Id : ujm-00677304, version 1

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Razvan Stoian, Jean-Philippe Colombier. Designer pulses for optimal ablation: guiding heat in ultrafast laser ablation plasmas. Advanced Laser Technologies, Sep 2011, Golden Sands, Bulgaria. 〈ujm-00677304〉

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