Dynamics of plasma propagation and splitting during pulsed-laser ablation

Summary form only given. Pulsed laser ablation has become a well-established technique for depositing thin films of many different types of technologically important materials. Deposition is usually carried out in a low-pressure ambient background gas to aid in control of the process or to promote interactions in the gas phase. Consequently, the theoretical analysis of the dynamics of the laser-generated plasma plume in the presence of a background gas has generated widespread interest. Experimentally, it is found that the plume frequently spits into two components, one traveling at near-vacuum velocity and the other greatly slowed by interaction with the background gas. Purely hydrodynamic descriptions of the plume-background system have been unable to describe this "plume splitting". A new approach to the problem, based on a combination of multiple scattering and hydrodynamic formulations has been developed. Although relatively simple in structure, the model gives excellent fits to various experimental data for Si in background gases of He and Ar, including the previously unexplained splitting of the ablated plume. It allows the plume to be broken up into scattering order, for which particles undergo 0, 1, 2, ... collisions with the background.