Response to “Comment on ‘Emission of prompt electrons during excimer laser ablation of aluminum targets’ ” [Appl. Phys. Lett. 76, 248 (2000)

Abstract

In a comment on our recent letter, Hong and Lu questioned that the sharp peak in the time-of-flight (TOF) signal observed during laser ablation of the Al target in vacuum was due to photoelectrons produced by laser target interaction. In particular, they claimed that very similar signals have been observed during KrF excimer laser ablation of Cu targets in ambient air at a laser fluence of 9.2 J cm−2 and with a probe placed at 0.75 and 1.8 mm apart from the target surface. In a recent article, such signals have been ascribed to plasma induced electric fields at early stages of the laser ablation process, when the emitted electrons and positive ions are in fast dynamics. We wish to point out that the analogy between the two electric signals is only apparent. In fact, the experimental approach by Lu and Hong is based on the detection of electromagnetic signals due to the emitting dipole formed by electrons and ions in the plume. This is realized by a tiny metal probe put nearby the target (<1 cm). Both the r−2 dependence of the signal amplitude (r being the probe distance) and the independence of the peak position on r ensure that the signal they observed was due to electromagnetic radiation.