Analyses of the TiO-γ system for temperature measurements in a laser-induced plasma

Emission spectra of TiO molecules in the spectral range from 700 to 720 nm have been recorded during pulsed-laser ablation of Ti in a low-pressure O2 atmosphere. The observed emission bands belong to the Δv = 0 and Δv = + 1 vibrational sequences of the γ-system (A 3Φ-X 3Δ) of TiO. According to the relative high temperatures in the laser-induced plasma of the order of 104 K, vibrational and rotational states with large quantum number are populated. Thus, the recorded spectra result from the superposition of more than 104 rotational lines belonging to 30 different vibrational bands. For the determination of the rotational and vibrational temperatures, the complicated structure of the TiO-γ emission spectrum has been reproduced using computer simulations. As a result, the gas kinetic temperature of the laser-induced plasma has been measured as a function of time and space for different O2 pressures. The temperature measurements are useful for a better understanding of the chemical processes during thin-film deposition by reactive laser ablation. In addition, simple empirical relations have been derived for temperature determination from the TiO-γ emission spectrum in the range from 3×102 to 2×104 K.