Hydrodynamics of particle formation following femtosecond laser ablation

Abstract

Ablation driven by intense, femtosecond laser pulses offers a novel route to fabrication of nanometer-sized particles. I model particle formation by considering the hydrodynamics of material expansion into vacuum. Modeling reveals rapid material dilution and cooling. Vacuum expansion is found to quench the ejected material 1–3 orders of magnitude more efficiently than thermal conduction quenches the residual bulk surface. Efficient quenching implies that solid-phase particles are produced rapidly (in ≪1 ns) following laser excitation; this may allow unique material states to be frozen within the ejected particles. Finally, the mean particle size is estimated to range from ∼1 to ∼10 nm for initial lattice temperatures ranging from 0.3 to 10 eV.