Optical emission and nanoparticle generation in Al plasmas using ultrashort laser pulses temporally optimized by real-time spectroscopic feedback

Journal Article · Thu Jul 15 00:00:00 EDT 2010 · Physical Review. B, Condensed Matter and Materials Physics

DOI:https://doi.org/10.1103/PHYSREVB.82.035430· OSTI ID:21389253

Guillermin, M; Colombier, J P; Audouard, E; Garrelie, F; Stoian, R ^[1]; Valette, S ^[2]

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1. Laboratoire Hubert Curien, UMR CNRS 5516, Universite de Lyon, Universite Jean Monnet, 42000 Saint-Etienne (France)
2. Laboratoire de Tribologie et Dynamique des Systemes, UMR CNRS 5513, Ecole Centrale de Lyon, 69134 Ecully (France)

With an interest in pulsed laser deposition and remote spectroscopy techniques, we explore here the potential of laser pulses temporally tailored on ultrafast time scales to control the expansion and the excitation degree of various ablation products including atomic species and nanoparticulates. Taking advantage of automated pulse-shaping techniques, an adaptive procedure based on spectroscopic feedback is applied to regulate the irradiance and enhance the optical emission of monocharged aluminum ions with respect to the neutral signal. This leads to optimized pulses usually consisting in a series of femtosecond peaks distributed on a longer picosecond sequence. The ablation features induced by the optimized pulse are compared with those determined by picosecond pulses generated by imposed second-order dispersion or by double pulse sequences with adjustable picosecond separation. This allows to analyze the influence of fast- and slow-varying envelope features on the material heating and the resulting plasma excitation degree. Using various optimal pulse forms including designed asymmetric shapes, we analyze the establishment of surface pre-excitation that enables conditions of enhanced radiation coupling. Thin films elaborated by unshaped femtosecond laser pulses and by optimized, stretched, or double pulse sequences are compared, indicating that the nanoparticles generation efficiency is strongly influenced by the temporal shaping of the laser irradiation. A thermodynamic scenario involving supercritical heating is proposed to explain enhanced ionization rates and lower particulates density for optimal pulses. Numerical one-dimensional hydrodynamic simulations for the excited matter support the interpretation of the experimental results in terms of relative efficiency of various relaxation paths for excited matter above or below the thermodynamic stability limits. The calculation results underline the role of the temperature and density gradients along the ablated plasma plume which lead to the spatial distinct locations of excited species. Moreover, the nanoparticles sizes are computed based on liquid layer ejection followed by a Rayleigh and Taylor instability decomposition, in good agreement with the experimental findings.

• OSTI ID: 21389253
• Journal Information: Physical Review. B, Condensed Matter and Materials Physics, Vol. 82, Issue 3; Other Information: DOI: 10.1103/PhysRevB.82.035430; (c) 2010 The American Physical Society; ISSN 1098-0121
• Country of Publication: United States
• Language: English

Related Subjects

75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ABLATION
ALUMINIUM IONS
ASYMMETRY
COUPLING
DECOMPOSITION
DENSITY
DISPERSIONS
EFFICIENCY
EMISSION
ENERGY BEAM DEPOSITION
EXCITATION
EXPANSION
FEEDBACK
HEATING
INSTABILITY
IONIZATION
LASER RADIATION
LAYERS
LIQUIDS
NANOSTRUCTURES
ONE-DIMENSIONAL CALCULATIONS
PEAKS
PLASMA
PULSED IRRADIATION
RADIANT FLUX DENSITY
RELAXATION
SIMULATION
SPECTROSCOPY
STABILITY
SURFACES
THIN FILMS
CHARGED PARTICLES
CHEMICAL REACTIONS
DEPOSITION
ELECTROMAGNETIC RADIATION
ENERGY-LEVEL TRANSITIONS
FILMS
FLUIDS
FLUX DENSITY
IONS
IRRADIATION
PHYSICAL PROPERTIES
RADIATIONS
SURFACE COATING