Experimental investigations of aluminum monoxide in the laser ablation of alumina

The laser ablation of alumina (AI₂O₃) is experimentally investigated by the use of ultra high speed photography, scanning electron microscopy, quadrupole mass spectroscopy, and time-resolved optical spectroscopy. Irradiance levels of typically 5 GW/cm² frequency quadrupled Nd:YAG laser radiation are applied to achieve uv laser ablation. Of primary interest is the optical spectroscopy of the aluminum monoxide (AlO) blue-green Β²&Sigma⁺ -> Χ²&Sigma⁺ band system that dominates the emission spectra some 20 μs after the short pulse, high peak power laser surface interaction. Com parisons with synthetic spectra that are computed by the use of accurate diatomic line strengths indicate AlO temperatures well in excess of 3,000 K. Monte-Carlo simulations are implemented to estimate the precision of the temperature obtained from (1) least-square fitting the entire measured spectrum, and (2) applying Boltzmann plot methods and Savitzky-Golay numerical filters to extract spectral peaks. The spectroscopic temperature obtained from both approaches (1) and (2) are typically within two standard deviations and show a precision on the order of 1%.