title: Multi-time step modeling of plume dynamics in nanosecond-scale carbon ablation.
abstract: The time span of plume dynamics in laser ablation of carbon ranges from nanoseconds to milliseconds. Multi-time step approach is developed to study the plume dynamics over this entire range with minimum requirements of numerical computational resources. This approach is applied to study one of the important aspects of nanosecond-scale laser ablation, namely the shielding of incident laser beam with previously ejected plumes. Capturing the shielding effect requires smaller than nanosecond-scale time step because of large velocity and pressure gradients in plume. Use of this time step over the entire domain needs enormous amount of computer time to cover the whole time span of plume dynamics. Multi-time step modeling for such an application is therefore useful. In general, for nanosecond-scale laser ablation this shielding is caused by ionized particles and by gas molecules. It is shown for carbon plume resulting from the nanosecond-scale lasers that the degree of ionization is small. Ionization of ablated carbon is estimated by Saha equation for the given initial plume conditions. The shielding of incident laser beam is therefore calculated by normal molecular absorption. The laser-light intensity that reaches the target for subsequent pulses is evaluated.
authors.affiliation: Department of Mechanical Engineering, The University of Akron, Akron, OH 44325-3903, USA.
authors.forename: Kedar
authors.initials: K
authors.lastname: Pathak
authors.forename: Alex
authors.initials: A
authors.lastname: Povitsky
mesh_terms: D002244:Carbon / Q000737:chemistry* / Q000528:radiation effects; D003198:Computer Simulation; D003460:Crystallization / Q000379:methods*; D005740:Gases / Q000737:chemistry; D006358:Hot Temperature; D007700:Kinetics; D007834:Lasers; D046911:Macromolecular Substances / Q000737:chemistry; D008422:Materials Testing; D008956:Models, Chemical; D008958:Models, Molecular; D008968:Molecular Conformation; D036103:Nanotechnology / Q000379:methods*; D037742:Nanotubes, Carbon / Q000737:chemistry* / Q000648:ultrastructure*; D010316:Particle Size; D013499:Surface Properties; D013997:Time Factors
chemical_list: D005740:Gases; D046911:Macromolecular Substances; D037742:Nanotubes, Carbon; D002244:Carbon