Analytica chimica acta · 2026
In situ imaging of oxidation dynamics within aluminum laser induced plasmas.
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Borrero-Negrón Justin I, Hartig Kyle C
Аннотация
BACKGROUND: Laser ablation (LA) methods underpin a wide class of analytical techniques, including laser-induced breakdown spectroscopy (LIBS), LA-ICP-MS, and laser ablation molecular spectrometry. Yet, interpretation of these signals remains limited by an incomplete understanding.
RESULTS: Here we integrate fast-gated emission spectroscopy with planar laser-induced fluorescence (PLIF) to map excited- and ground-state Al/AlO produced by nanosecond (1064 nm, ∼6 ns, 35 mJ) ablation of Al at 150 Torr with controlled oxygen mole fractions [Formula: see text] . Targeted transitions include Al I at 394/396 nm and the AlO B2Σ+→X2Σ+ system (440-530 nm); emission images used 1 nm FWHM bandpass filters (396 and 487 nm), and PLIF probed Al at 394 nm and AlO at 464 nm with detection at 396 nm and 487 nm, respectively. Time-resolved emission revealed that AlO production peaked at 25-33 μs depending on oxygen content, while PLIF identified ground-state shells that encapsulated excited species, driving distinct stages of plume evolution: expansion, collapse, and stagnant intermixing. In contrast to emission-only studies that ascribed AlO formation largely to post-shock-collapse chemistry, our direct probing of Al and AlO reveals a finite mixing layer at the contact surface and shows AlO encapsulating the emission-bright core during expansion and collapse, clarifying the spatial origin of oxidation within the plume. This joint diagnostic refines shock-mediated interpretations derived from spontaneous emission alone by resolving ground-state speciation and internal flow structures (including onset of vortex formation coincident with peak AlO), thereby establishing when and where oxidation proceeds in LA plumes used as surrogates for post-detonation fireballs. Quantitative trajectory analysis showed that early expansion followed Sedov-Taylor blast-wave scaling, with later descent and confinement captured by drag and semi-empirical models. Relative to emission-only LIBS, the joint modality improves selectivity against a continuum background and resolves ground-state speciation and internal flow structures (including a contact surface mixing layer and toroidal-vortex formation) that are not accessible by emission alone, clarifying when and where oxidation initiates and how reactive environments shape LIBS signal formation.
SIGNIFICANCE: These results strengthen the analytical basis for LA across platforms, improving interpretation and quantitation in LIBS and informing the fidelity of LA surrogates for post-detonation fireballs, and provide method details (gating, spectral windows, replication) that enhance reproducibility and transfer to other LA matrices.
RESULTS: Here we integrate fast-gated emission spectroscopy with planar laser-induced fluorescence (PLIF) to map excited- and ground-state Al/AlO produced by nanosecond (1064 nm, ∼6 ns, 35 mJ) ablation of Al at 150 Torr with controlled oxygen mole fractions [Formula: see text] . Targeted transitions include Al I at 394/396 nm and the AlO B2Σ+→X2Σ+ system (440-530 nm); emission images used 1 nm FWHM bandpass filters (396 and 487 nm), and PLIF probed Al at 394 nm and AlO at 464 nm with detection at 396 nm and 487 nm, respectively. Time-resolved emission revealed that AlO production peaked at 25-33 μs depending on oxygen content, while PLIF identified ground-state shells that encapsulated excited species, driving distinct stages of plume evolution: expansion, collapse, and stagnant intermixing. In contrast to emission-only studies that ascribed AlO formation largely to post-shock-collapse chemistry, our direct probing of Al and AlO reveals a finite mixing layer at the contact surface and shows AlO encapsulating the emission-bright core during expansion and collapse, clarifying the spatial origin of oxidation within the plume. This joint diagnostic refines shock-mediated interpretations derived from spontaneous emission alone by resolving ground-state speciation and internal flow structures (including onset of vortex formation coincident with peak AlO), thereby establishing when and where oxidation proceeds in LA plumes used as surrogates for post-detonation fireballs. Quantitative trajectory analysis showed that early expansion followed Sedov-Taylor blast-wave scaling, with later descent and confinement captured by drag and semi-empirical models. Relative to emission-only LIBS, the joint modality improves selectivity against a continuum background and resolves ground-state speciation and internal flow structures (including a contact surface mixing layer and toroidal-vortex formation) that are not accessible by emission alone, clarifying when and where oxidation initiates and how reactive environments shape LIBS signal formation.
SIGNIFICANCE: These results strengthen the analytical basis for LA across platforms, improving interpretation and quantitation in LIBS and informing the fidelity of LA surrogates for post-detonation fireballs, and provide method details (gating, spectral windows, replication) that enhance reproducibility and transfer to other LA matrices.