Effect of ambient on the dynamics of re-deposition in the rear laser ablation of a thin film

In this work, we report an innovative pump-probe based experimental set up, to study the melting, subsequent evaporation, plasma formation and re-deposition in a thin film coated on a glass substrate under different ambient conditions and laser fluences. The ambient conditions restrict the expansion of the plasma plume. At high ambient pressure, plume expansion stops closer to the substrate and gets re-deposited at the site of the ablation. This helps in the identification of multiple processes and their temporal evolutions during the melting, expansion and re-deposition stages. The ambient conditions affect the plasma plume formed upon ablation, thus modulating the transmission of probe laser pulses, which provides information about the plume dynamics. Further, the study offers valuable insights into the laser-based ablation of thin film coatings, which will have implications in situ cleaning of view ports on large experimental facilities such as tokamaks and other systems e.g. coating units, pulsed laser deposition, Laser induced forward transfer, Laser surface structuring, etc.