Influence of CO₂ pressure on the emission spectra and plasma parameters in underwater laser-induced breakdown spectroscopy.

Optical emission spectroscopic studies have been carried out to investigate the pressure effect of CO₂ on laser-produced underwater plasma. The plasma was generated by focusing 1064 nm, 6 ns pulses from a Nd:YAG laser in a CO₂-bearing solution. The temporal evolution of the continuum emission, Sr and Ba lines, and plasma electron density and temperature was characterized under CO₂ pressure ranging from 10 to 300 bars. The electron density measurements were made using the Stark broadening of the 455.40 nm Ba II line, while the temperature measurements have been performed by the Saha-Boltzmann method using the Sr I-II lines at 460.73 and 407.77 nm, respectively. It was found that CO₂ pressure has little effect on the emission line intensity and signal-to-background ratio. The electron density and the temperature are found to be independent of the CO₂ pressure at early times. When time becomes longer, the electron density exhibits an appreciable rise as the CO₂ pressure increases, while the temperature is found to be unchanged.