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

• 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.

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.