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 O 2 atmosphere. The observed emission bands belong to the Δ v = 0 and Δ v = + 1 vibrational sequences of the γ-system (A 3 Φ-X 3 Δ) of TiO. According to the relative high temperatures in the laser-induced plasma of the order of 10 4 K, vibrational and rotational states with large quantum number are populated. Thus, the recorded spectra result from the superposition of more than 10 4 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 O 2 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 × 10 2 to 2 × 10 4 K.