LASER-ABLATION PLUME THERMALIZATION DYNAMICS IN BACKGROUND GASES - COMBINED IMAGING, OPTICAL-ABSORPTION AND EMISSION-SPECTROSCOPY, AND ION PROBE MEASUREMENTS

Combined diagnostic measurements are employed to characterize the pene tration of energetic ablation plumes through background gases during a key transitional regime in which the ion flux is observed (with fast ion probes) to split into distinct fast and slowed components. This ap parently general phenomenon occurs over a limited range of distances a t ambient pressures typically used for PLD (as reported for YBCO ablat ion into O-2) [1-5] and may be important to film growth by PLD because a 'fast' component of ions can arrive at the probe (or substrate) wit h little or no delay compared to propagation in vacuum (i.e., high 10- 100 eV kinetic energies). At longer distances, this 'fast' component i s completely attenuated, and only slowed distributions of ions are obs erved. interestingly, this 'fast' component is easily overlooked in im aging studies because the bright plume luminescence occurs in the slow ed distribution. Time- and spatially-resolved optical absorption and e mission spectroscopy are applied to experimentally determine the compo sition of the 'fast' and 'slow' propagating plume components for a sin gle-component target ablation (yttrium) into an inert gas (argon) for correlation with quantitative imaging and ion probe measurements. The yttrium/argon system was chosen because optical absorption spectroscop y of both Y and Y+ was simultaneously possible [9] and the inert natur e of argon. Experimental results for several other systems, including Si/Ar, Si/He, YBCO/O-2 are presented to illustrate variations in scatt ering mechanisms. Species-resolved imaging of YO and Ba* is presented for the YBCO/O-2 system to illustrate the similarities and difference s in the spatial regions of observed luminescence, These measurements confirm that, in addition to the bright significantly-slowed front whi ch has been described by shock or drag propagation models [1], a fast- component of target material is transmitted to extended distances for some ambient pressures with near-initial velocities.