Temporal evolution study of the plasma induced by CO2 pulsed laser on targets of titanium oxides

This paper reports studies on time-resolved laser induced breakdown spectroscopy (LIBS) of plasmas induced by IR nanosecond laser pulses on the titanium oxides TiO and TiO2 (anatase). LIBS excitation was performed using a CO2 laser. The laser-induced plasma was found strongly ionized yielding Ti+, O+, Ti2+, O2+, Ti3+, and Ti4+ species and rich in neutral titanium and oxygen atoms. The temporal behavior of specific emission lines of Ti, Ti+, Ti2+ and Ti3+ was characterized. The results show a faster decay of Ti3+ and Ti2+ ionic species than that of Ti+ and neutral Ti atoms. Spectroscopic diagnostics were used to determine the time-resolved electron density and excitation temperatures. Laser irradiation of TiO2-anatase induces on the surface sample the polymorphic transformation to TiO2-rutile. The dependence on fluence and number of irradiation pulses of this transformation was studied by micro-Raman spectroscopy. - Highlights: • Plasma plumes of Titanium oxides have been characterized by high resolution LIBS. • Emissions are due to relaxation of excited Ti+, O+, Ti2+, O2+, Ti3+, and Ti4+. • Plasma temperature is measured at different delays, the maximum is around 23,000 K. • The electron density value after 0.1 μs is nearly constant around 6 × 1016 cm−3. • Above ablation threshold, anatase–rutile transformation shows an incubation effect