Generating conditions of argon laser-sustained plasma by disk, fiber and diode lasers

Abstract

Laser-sustained plasma (LSP) is a promising method for high-pressure plasma generation that overcomes the problems of arc discharge. Then, the generating conditions of argon LSP were investigated using a kilowatt class disk, fiber and diode lasers. For the disk and fiber lasers, the threshold laser power for LSP generation was found to decrease with pressure. The minimum laser power of the disk and fiber lasers was 1.1 kW at a pressure of 1.5 MPa and 0.45 kW at a pressure of 2.0 MPa. The threshold power of the disk laser was higher than that of the fiber laser. The fiber laser might have a lower threshold because atomic line absorption occurs at 1067 nm and 1068 nm since both absorption coefficients achieved through the Bremsstrahlung process are almost the same. Since LSP could not be generated by a diode laser at a pressure of less than 6.5 MPa, the generating conditions were estimated based on the product of the absorption coefficient of laser intensity. A pressure of more than 8 MPa was found to be necessary for a laser with 1 kW of power, and laser power of more than 109 kW is necessary for a pressure of 0.1 MPa.