Evaluation of atomic absorption of laser-sustained argon plasma using a diode laser

Abstract

In our previous studies, xenon (Xe), krypton (Kr), and argon (Ar) laser-sustained plasmas (LSPs) were generated using a diode laser, and the minimum laser power required to generate each plasma was investigated. Although argon has a larger ionization energy than that of krypton (≥1.6 MPa), the argon LSP was generated at a smaller laser power than that of the krypton LSP because atomic absorption occurs in the argon LSP, which contributes to generating LSPs. In this study, we investigated the fractional absorption of an argon LSP from the transmitted laser power using a diode laser. Fractional absorption increased with increasing pressure and a decreasing F number. The maximum fractional absorption was approximately 40%. Furthermore, we evaluated the effects of inverse bremsstrahlung and atomic absorptions for calculations. These two absorption processes result in the same amount of absorption. Furthermore, the measured fractional absorption matches the theoretical values. These calculations were correct, and the atomic absorption was effective in generating the LSP.