A spectroscopic study of laser ablation plasmas from Ti, Al and C targets

We performed time- and space-resolved plasma diagnostics during ablation of Ti, Al and C targets in low-pressure nitrogen atmospheres using pulsed nanosecond UV lasers. From spectral lines emitted from ions during the early plasma phase, we deduced electron density and electron temperature while the gas kinetic temperature was estimated from vibrational sequences of molecular spectra. In the case of metal targets, a dense and highly ionized plasma in local thermal equilibrium was formed near the target surface for laser intensities of about 400 MW cmy2. For carbon, a much higher laser intensity was necessary to induce significant plasma ionization. During its propagation through the ambient gas, the plasma recombined and neutral atoms, molecules and clusters were formed. Gas-phase reactions were observed to be the dominant source of CN formation. q1998 Elsevier Science B.V.