Interaction Of Flows Of Laser Ablation Plasmas

Our studies of laser pulsed deposition of thin films, using 20-ns second-harmonic Nd:YAG laser operated at a few GW/cm(2), show that introduction of an obstacle like a grid screen into ablation plume with typical density 10(18) cm(-3) and temperature 3 eV substantially affects dynamics of plasma expansion and results in dramatic changes of plasma parameters. In this work, we report the effects typical for the later stage of plasma-grid interaction - effects related to the interaction of multiple plasma flows. Model experiments. performed employing method of emission spectroscopy, time-of-flight technique, and plasma imaging with CCD camera, show significant variation of plasma composition and transformation of velocity distribution due to plasmas interaction. Two modes of such transformation have been observed: linear growth of density in the resulting flow, and formation of the additional slow peak in the velocity distribution. The effect is shown to be velocity-resonant.