TEMPERATURE-MEASUREMENTS DURING LASER-ABLATION OF SI INTO HE, AR AND O-2

Ablation of Si into He, Ar and O-2 atmosphere by excimer laser has bee n investigated to understand the formation of molecules and clusters. Temperature is an obvious parameter controlling the stability of diato mic molecules. In this paper we report the measurements, by laser indu ced fluorescence (LIF), of the temperature of Si atoms and rotational temperature of SiO in laser induced plasma. Thermal relaxation process es of atomic Si in He and Ar atmospheres have been studied by measurin g the Doppler profile of Si line using the 3d P-1(0)-3p(2) S-1 transit ion centered at 263.128 nm. The thermalization of Si atoms is slower i n Ar atmosphere than in He. The rotational temperature of SiO was meas ured by pumping the A(1) Pi-X(1) Sigma transition. In 5-400 mu s delay after ablation pulse, the SiO temperature decreases from 2000 to 400 K. No evidence of nonequilibrium of the rotational and vibrational mod es was observed. LIF measurements indicate that the formation of SiO m olecules is better visualized as a gas phase equilibrium reaction rath er than a ballistic collision in the temperature range 400-2000 K.