New Method of Laser Plasma Spectroscopy for Metal Samples Using Metastable He Atoms Induced by Transversely Excited Atmospheric-Pressure CO2 Laser in He Gas at 1 atm

Abstract

A high-power transversely excited atmospheric-pressure (TEA) CO2 laser (600–1500 mJ) was focused on a metal target in surrounding He gas at 1 atm to produce strong He gas breakdown plasma, while leaving the metal surface undamaged, and a Q-switched Nd:YAG laser (60–90 mJ) was also simultaneously focused on the metal surface to be ablated at a slightly shifted spot position with various delay times (0–150 µs) relative to the TEA CO2 laser. It was concluded that the ablated atoms from the metal sample enter the He gas plasma region and are excited by metastable He atoms, which are produced in very large quantities in the He gas plasma region. Due to the fact that He gas plasma works as an exciting source with a very long lifetime (about 100 µs), the detected atomic emission lines are very narrow in spectral width with a very low background spectrum, and also the atomic emission spectrum profile does not follow the Boltzmann distribution during the long emission life. We call this new method LIPS-He*. This new method has high potential for realizing in situ high-sensitivity analysis.