Evidence for the physical basis and universality of the elimination of particulates using dual-laser ablation. II. Dynamic time-resolved target reflectivity of metals and film growth of Zn

摘要

We have presented, in Part I of this series of two articles, the applicability of dynamic melt studies of the surface of a target under pulsed CO_(2) laser radiation to determine the onset of melt in these targets. Determination of this time and the accurate synchronization of an excimer (KrF) laser to coincide with the onset of melt on the target surface was shown to lead to particulate-free film deposition for Y_(2)O_(3) and ZnO films. A key feature of the pump-probe reflectivity studies was the dynamic enhancement of the reflected probe signal, indicating the onset of melt. Some metallic targets, depending on the diameter of the precursor powder globules, such as the zinc target used in this study, do not yield such observable enhancements. In this article (Part II) we present the determination of the time for ablation of a variety of metallic targets under pulsed CO_(2) laser radiation, by monitoring the dynamic target reflectivity. The melt time is either directly determined or, in the absence of observable melt, estimated based on a simple thermal model for the absorption of the laser radiation by the target. Correlation of the calculated melt times with the morphological quality of particulate-free film growth of Zn is demonstrated. The effect of variable CO_(2) laser fluence on the deposited films is also demonstrated. The universality of applicability of the target reflectivity studies to a wide range of dissimilar materials, as well as the physical basis for the removal of particulates in dual-laser ablation is established.