Characteristics of Krypton and Krypton-Based Mixed Gases Laser-Sustained Plasma Using a 4-kW Laser Diode

Although diode lasers are highly efficient, low-cost, and easy-to-maintain light sources, their utilization to produce laser-sustained plasmas (LSPs) has been limited to xenon because of their poor beam parameter products. In this study, LSPs using krypton, krypton/argon, and krypton/helium as substitutes for expensive xenon, were successfully generated and characterized using a 4-kW-class diode laser. The minimum laser power for Kr LSP generation decreased to 3580 W with pressure. The maximum ratio of the other gas to krypton was greater than 50% for argon and 23% for helium. The LSP temperature estimated from measured krypton atomic lines ranged from 11 500 to 15 700 K. Finally, the fractional absorption was estimated from the absorption coefficient calculated using the measured temperature and LSP length. The fractional absorption of the Kr LSP increased to 0.24 with pressure, whereas that of the Kr/Ar and Kr/He LSP was approximately 0.05 for the variation of pressure.