The plasma plume created during photoablation of various
targets by an excimer KrF laser beam is studied in typical conditions
of pulsed laser film deposition. For the examination of transport
phenomena of ejected species, the space and time resolved evolution
of the luminous plume is investigated by fast imaging as a function
of laser fluence (from 7 to $200~\mathrm{J/cm}^{2}$) and nitrogen background
pressure (from 5 × 10−3 to 500 Pa) for five different target
materials (boron nitride, graphite, alumina, molybdenum, a superconducting oxide YBCO).
Under "vacuum" (5 × 10−3 Pa and for nitrogen background
pressures up to 10−1−1 Pa, the plume expands freely. For higher
background pressures $(\geq 10~\mathrm{Pa})$, three successive
regions above the target can be distinguished: at first the
expansion is free, then the plume expands according to a shock
wave-like behaviour, and lastly a drag force model correctly
describes the plume shape evolution. Velocities of the luminous
plasma front and of the "mass center" of the plume are determined
versus laser fluence and background nitrogen gas pressure.