EFFECT OF DIFFERENT ATMOSPHERES ON THE EXCITATION PROCESS OF TEA-CO-2 LASER-INDUCED SHOCK-WAVE PLASMA

The plasma characteristics and excitation process of laser-induced plasma with the use of a TEA CO2 laser of 750 mJ pulse energy and 100 ns pulse width are studied in different surrounding gases at reduced pressures. From the time-resolved spatial distribution, it is clear that in helium and argon atmospheres, two different excitation processes take place in forming the plasma. The first excitation process is due to the blast wave, while the second process is due to the metastable state of the noble gases. It is believed that this second process transfers meta-stable energy to the vaporized atoms of the target for emission, even long after the laser bombardment ends, thus giving total emission intensity that is higher in the noble gases than in air. The displacement of the front of the emission line under different atmospheres is also presented.