Propagation dynamics of a LaMnO3 laser ablation plume in an oxygen atmosphere

The effect of ambient gas on the expansion dynamics of the plasma plume generated by excimer laser ablation of a LaMnO3 target is investigated by using fast photography. The plume propagation in an oxygen environment is examined with pressure ranging from vacuum to a few millibars. Imaging analysis performed over a complete set of images of the plume emission, for each pressure, has allowed following the changes in the plume structure, the plume front dynamics and stopping length, as well as the variation of plume angular distribution as a function of time and pressure. Our experimental findings evidence a number of interesting effects occurring at various times of the expansion and at different pressure levels. At low pressure (< 10(-2) mbar) the plume expands freely resembling the propagation in high vacuum condition. Then, at intermediate pressure levels (10(-2)-1 mbar) spatial splitting of the plume, plume front oscillations, plume broadening and sharpening, and, finally, plume stopping are observed as a function of the expansion time. The plume stopping length and the asymptotic angular width of the plume as a function of the pressure are analyzed and discussed. The expansion dynamics of the plume front is examined by means of a theoretical description of plume evolution and shock-wave propagation, which considers distance-related pressure dimensionless variables, resulting in a fairly good agreement.