Effect of Laser Energy on Spectral Emission from a Plasma Induced by a Q-switched Nd Laser in Different Atmospheres

The effect of the laser energy on the intensity of the spectrum of a Q-switched laserinduced plasma in different reduced atmospheres, Ar, He, and air was studied by changing the laser pulse energy over a range of 20 to 95 mJ. At low pressure, the emission intensity increases linearly with increasing the laser energy for three kinds of gases. However, at high pressure near atmospheric pressure, the more intense emission intensity can be obtained by increasing the laser energy for He, while for Ar and air, higher laser energy does not bring about high emission intensity. The cause for this is discussed briefly in terms of the gas breakdown and self-absorption.