Temperature measurements during laser ablation of Si into He, Ar and O2

Ablation of Si into He, Ar and O2 atmosphere by excimer laser has been investigated to understand the formation of molecules and clusters. Temperature is an obvious parameter controlling the stability of diatomic molecules. In this paper we report the measurements, by laser induced fluorescence (LIF), of the temperature of Si atoms and rotational temperature of SiO in laser induced plasma. Thermal relaxation processes of atomic Si in He and Ar atmospheres have been studied by measuring the Doppler profile of Si line using the 3d 1P0−3p2 1S transition centered at 263.128 nm. The thermalization of Si atoms is slower in Ar atmosphere than in He. The rotational temperature of SiO was measured by pumping the A1φ−X1Σ transition. In 5–400 μs delay after ablation pulse, the SiO temperature decreases from 2000 to 400 K. No evidence of nonequilibrium of the rotational and vibrational modes was observed. LIF measurements indicate that the formation of SiO molecules is better visualized as a gas phase equilibrium reaction rather than a ballistic collision in the temperature range 400–2000 K.