Expansion dynamics of ultrafast laser produced plasmas in the presence of ambient argon

We investigated the expansion dynamics of fs laser ablated brass plasma in Ar at various pressure levels ranging from 10^-5Torr to atmospheric conditions using time-resolved and spectrally resolved two-dimensional imaging. Significant changes in plume morphology were noticed at varying pressure levels which included free expansion, spherical to cylindrical geometry changes, sharpening, and confinement. The temporal evolution of excited Cu and Zn species in the plume were imaged using narrow band-pass interference filters, and their hydrodynamic expansion features were compared. 2D imaging coupled with monochromatic line selection showed velocity differences, uneven distribution, and aspect ratio differences among the plume species. Plume morphological changes were found to be significant at intermediate pressure levels (∼10Torr) where plasma emissivity was found to be maximum. The expansion features of plume were compared with various models and found to be generally in good agreement.