Experimental and theoretical investigation of nonequilibrium in laser induced plasmas

Expansion of the material ablated from a TiO (titanium oxide) surface with a nanosecond pulsed laser is studied by emission spectroscopy. The quantities measured are the time of flight and a space resolved spectrum. The Boltzmann plot approach is used to obtain temperatures and concentrations of Ti (titanium) atoms and ions. A semi-empirical collisional-radiative model is shown to be very useful to eliminate spurious effects from the spectrum. A self-consistent model coupling collisional/radiative kinetics and fluid dynamic equations of the plume expansion can improve the understanding of the physics during the expansion ad can be used as a powerful tool to extract quantitative information from the emission spectrum even in the absence of LTE (local thermodynamic equilibrium). © 2001 by G.Colonna.