Generation of Argon Laser-Sustained Plasma using Diode Laser

Argon laser-sustained plasma (LSP) was generated using a 4-kW-class diode laser at pressures of 1.55-2.00 MPa. It was found that there is a tendency of the minimum laser power for LSP generation to decrease from 4,200 W to 2,850 W as the pressure increases. The temperature estimated based on emission spectroscopy was approximately 12,000 K for the variation of pressure and the laser power of 4,350 W. Because the estimated absorption coefficient increases with pressure assuming the inverse bremsstrahlung process, the decrease in minimum laser power as pressure increases pressure is consistent with the increase in the absorption coefficient. There was no significant tendency in temperature change as pressure increased. Furthermore, the inverse bremsstrahlung coefficient tended to increase slightly as pressure increased. This is because the electron number density increases as pressure increases at the same temperature. Therefore, the laser power for LSP generation decreases as pressure increases.