The laser-induced plasma persistence time extension in low pressures using the ablated mass confinement method

The laser-induced plasma characteristics are strongly dependent on the surrounding pressure. Confining of the rapidly expanding plasma at low pressure conditions has shown that it is possible to perform the laser-induced breakdown spectroscopy (LIBS) detection by using a long gate width CCD detector. The acrylic window is placed above the sample for adjusting the plasma confining height for optimally extending the plasma persistence time. At 1 mm confining height at 1 torr, the signal intensity of Al III emission (452.8945 nm) was enhanced up to 5.5 times the free expansion case. The signal intensity was markedly lower at 760 torr as thickness of the window became larger, whereas it was constant at 1 torr. It is suggested that optimum detection scheme as opposed to generation of strong plasma is more important in the low pressure LIBS study. The laser energy required for aluminum detection was only 3.664 mJ/pulse at 1 torr. The key aspect of this successful detection is the combined ablated mass confinement and the low pressure detection. This method has the potential to lead the detection of minor elements in metals at an increased sensitivity.