Temporal evolution of laser-ablated Coq ions probed by time-of-flight mass spectrometry

A pulsed-field time-of-flight mass spectrometric TOFMS.technique was used to investigate the expansion dynamics of the ionic species ejected from the visible ls532 nm.laser ablation of cobalt target at low laser fluence less than 1 Jrcm2. The temporal evolution of Coq ions was studied by varying the delay time of the ion repelling pulse with respect to the laser irradiation, which provides significant information on the ablated plume characterization. The obtained TOF mass spectra were well fitted by shifted Maxwell–Boltzmann distributions on a stream velocity, commonly used to describe the measured velocity distributions. The TOF distribution of Coq ions showed a bimodal distribution with fast and slow velocities. These velocities show a decreasing tendency with delay time, which is attributed to the gas collisions between the plume ejecta and to the related gas dynamics. The present results suggest that the in situ measurements of the most probable velocity of ablated ions along the normal to the solid target can be accomplished by the simple technique of a laser ablationrTOFMS. q1999 Elsevier Science B.V. All rights reserved.