Neutral and ionic emission in Q-switched Nd : YAG laser-induced shock waveplasma

Excitation mechanisms for copper and zinc atoms as well as their ionic spec ies in the Q-switched (Q-sw) Nd:YAG laser-induced shock wave plasma have be en investigated with a time-gated optical multichannel analyzer (OMA) syste m for various experimental conditions. It is demonstrated that the shock ex citation process is the main mechanism responsible for the emission spectra for laser energy ranging from 8 to 86 mJ and surrounding air pressure from 2 to 50 Torr, At air pressure below 2 Torr, collision-induced excitation a ppears to take over and becomes the operative mechanism. In all cases, the neutral emission dominates over the ionic emission, leading to a high signa l-to-background ratio, which tends to decrease, however, at higher laser en ergy and air pressure.