Emission spectroscopy of cw CO2 laser-sustained argon plasma: Effects of gas-flow speed

The effects of elevated gas-flow speed were studied for the cw CO₂ laser-sustained argon plasma in a chamber of 1-atm pressure using the argon emission spectrum. Electron temperature distribution was obtained from the 415.8-nm Ari line-to-continuum intensity ratio. This temperature distribution was further utilized to calculate the fraction of laser power absorbed by the plasma, and the amount of radiation loss from the plasma. The experiments were performed for laser powers of 2.5 and 5 kW with an f/7 lens focusing scheme, and gas-flow speeds of 2-10 m/s. The results show that as high as 86% of incident laser energy can be absorbed by the plasma. Accounting for the plasma radiation loss, 41%-62% of the laser energy can still be retained as the gas thermal energy, which is a significant increase over the previously reported results for lower flow speed and smaller focusing f number.