Basic aspects of LIBS

The rotational, vibrational and excitation temperatures in plasmas formed by Nd YAG and excimer lasers on graphite targets have been compared. Molecular emission from CN in the plasma was used to determine vibrational and rotational temperatures a small amount of Fe or Pb was added to the graphite target and the emission from a series of these lines was observed to determine excitation temperatures. While the excitation and vibration temperatures were similar, the rotation temperatures determined in each case were almost one order of magnitude lower than either the vibrational or excitation values. 

the rotational populations were such that it was impossible to determine a single temperature, possibly because different mechanisms of CN formation resulted in this multi-temperature distribution. The vibrational and rotational temperatures were higher for the excimer laser (308 nm induced plasmas) than for the Nd YAG laser (1064 nm plasmas), viz. 18 000 K versus 10 000 K. 

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