Time-resolved plasma imaging in microwave-assisted laser-induced breakdown spectroscopy

Abstract

To study the dynamics of luminous plasma induced by a pulse laser and microwaves (MWs), time resolved imaging of microwave-assisted laser-induced plasma was carried out. In this study, a luminous plasma was induced by a second harmonic Nd:YAG laser (532 nm, 8 ns, 5 J) on calcium oxide (Ca2O3) pellet at low pressure (5 Torr) of Ar gas. The luminous plasma was enhanced by intensified microwaves (MWs) generated from a magnetron. The image of plasma induced by laser has different features from the plasma induced by the laser with MWs. For the case of laser only, the plasma lifetime is approximately 50 μs, the plasma size at 5 μs is approximately 3 mm, and the neutral Ca emission is much brighter than the ionic Ca emission. When the MWs was introduced into the laser-induced plasma, the plasma emission was enhanced, namely the plasma lifetime was elongated of approximately 8 times, the plasma size at 5 μs was enlarged of approximately 3 times, and the ionic Ca emission is much brighter than the case of neutral Ca emission, which indicated that the plasma temperature is much higher than the case of laser only. Therefore, the plasma induced by the microwave-assisted laser can be effectively used for the analysis of elemental composition in materials with high sensitivity.