We report results from optical interferometric probing of a laser generated Zn plasma plume. The experiment was performed in a vacuum and O2 rich environments where the background pressure of O2 was maintained at 1000 Pa and the results from both regimes are compared. The focus of our work is very much on the early stages in the life of the plasma plume which remains, to date, a largely unexplored area of study, at least in the pulsed laser deposition research domain. It was found that the electron density profile normal to the target is different in the background gas at early times (30 ns) compared to that of the vacuum case. At later times (80 ns) both profiles have a very similar shape. We also observe the formation of a shock wave at the plasma–gas interface shortly after plasma breakdown (<15 ns).