DYNAMICS OF PLUME PROPAGATION AND SPLITTING DURING PULSED-LASER ABLATION

An innovative new approach has been developed for modeling the expansi on of laser-generated plumes into low-pressure gases where initially t he mean free path may be long enough for interpenetration of the plume and background. The model is based on a combination of multiple elast ic scattering and hydrodynamic formulations. Although relatively simpl e in structure, it gives excellent fits to new experimental data for S i in He and Ar, and provides for the first time a detailed, coherent e xplanation of the observed splitting of the plume into a fast and slow component.