Molecule formation induced by non-uniform plume–air interactions in laser induced plasma

Abstract

Measurements with Laser Ablation Molecular Isotopic Spectrometry (LAMIS) are usually performed in atmosphere for rapid isotope analysis, and an understanding of molecule formation via plasma–air chemical reactions is important for quantitative analysis by LAMIS. In this work, the expansion of a plasma plume from ablation of pure aluminum in air is studied with time- and space-resolved monochromatic imaging and emission spectroscopy. The distributions of neutral Al and O atoms and AlO radicals formed through plasma chemical reactions are characterized. The emission spectra of the AlO bands of a B²Σ⁺–X²Σ⁺ system are recorded and the rotational–vibrational temperature was obtained through fitting experimental spectra. Inter-molecular vibrational band interference is well re-constructed, and self-absorption of bandheads, especially for the (0–0) band, is corrected. Interpretation of the spatial–temporal evolutions of plasma species and plasma temperature provides insights into the formation mechanism of AlO radicals in laser-induced plasma.