Spectroscopic study of ablation and recombination processes in a laser-produced ZnO plasma
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Characteristics of laser-produced ZnO plasmas have been investigated by spectroscopic observations. In particular, the ablation dynamics and recombination process in vacuum or gas atmospheres (helium or oxygen) were studied on the basis of atomic physics. During and immediately after a laser irradiation, plasma parameters, such as electron temperature and electron density, were deduced from continuum and line spectra. In addition, the expansion velocities of ions and atoms were determined by time-of-flight transients of the emission spectra. As for the neutralization process of the expanding plasmas in vacuum, it was found that the radiative recombination dominated the plasma neutralization process. On the other hand, long-lived bright emissions that had a roughly spherical shape were observed in a helium atmosphere. This can be explained by the scattering of particles ejected from the target and rapid plasma cooling due to the collision with an ambient gas. Thus, the three-body recombination responsible for the intense emissions played an important role for electron-ion recombination. Moreover, it was found that a charge exchange recombination between He+ and Zn occurred near the target surface in helium. Although similar results were obtained in an oxygen atmosphere, the peak intensities were much higher than those in helium, implying that the additional cooling associated with the inherent properties of molecules may significantly influence the plasma neutralization.
- Journal of Applied Physics
Journal of Applied Physics 99(7), 2006-04-01
American Institute of Physics