Abstract
The laser-induced plasma (LIP) and the shock wave generated by pulsed laser ablation of a graphite target in air and reflected by a flat obstacle were examined by optical emission spectroscopy and probe beam deflection measurements. The interaction between the LIP and the shock wave and its effects on the expansion of the LIP as well as on the optical emission of carbon atoms were studied. The carbon atomic emission can be enhanced or reduced in the situation with a flat obstacle standing in the propagation path of the shock wave. The enhancement or reduction of the carbon atomic emission has a close connection with the shock wave generated by graphite ablation and reflected by the obstacle. The reflected shock wave confines the expansion of the LIP and impedes the travelling of the plasma species. The enhancement was observed at the detection position close to the target and with a short block-target distance. The shock wave thus reflected encounters the luminous LIP at its early expanding stage and confines the expansion of the LIP, resulting in the enhancement in the optical emission of carbon atoms. But at the detection position far from the target and with a longer block-target distance, a reduction in the optical emission due to spatial confinement was observed. The possible mechanisms responsible for the effects of spatial confinement on the optical emission were discussed.
Highlights
Ablation of a target by a focused pulsed laser beam vaporizes the surface materials of the irradiated area of the ablated target, inducing a luminous plasma composed of the species vaporized from the target surface
The behavior of a laserinduced plasma (LIP) is very different when it expands in a confined space as compared with that expanding in an open space, so is the behavior of the LIP species when they fly in a confined space as compared with those flying in an open space
Similar to our previous work, optical emission of several carbon-related species can be identified from the LIP produced by graphite ablation, including the emission bands emitted by diatomic CN and C2 molecules and the emission lines emitted by monoatomic carbon atoms and ions
Summary
Ablation of a target by a focused pulsed laser beam vaporizes the surface materials of the irradiated area of the ablated target, inducing a luminous plasma composed of the species vaporized from the target surface. Spatial confinement can enhance the emission intensity of the LIP with a ratio up to 10, which is of great interest for element detection and composition analysis based on laser induced breakdown spectroscopy (LIBS).. The reflected shock wave meets the expanding LIP, confining the LIP expansion and compressing the LIP volume. The spatial confinement and compression of the LIP by the reflected shock wave can be observed by time and space resolved optical emission spectroscopy (OES) and probe beam deflection (PBD) methods.. The LIP was generated by laser ablation of a graphite target in air and confined by the shock wave that was induced by target ablation and was reflected by a flat metal block used as the obstacle. It was found that the reflected shock wave plays an important role in the change of the optical emission emitted by LIP species. The correlation between the emission enhancement or reduction and the spatial confinement was examined for a discussion on the possible mechanism responsible for the changes in carbon emission
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