CO₂レーザーによるプラズマ生成過程のシミュレーション

抄録

In order to examine the basic characteristic of the plasma produced in experiments related to laser-induced lightning, computer simulations of the plasma production processes under CO₂ laser irradiation are conducted. The necessary conditions for the plasma production in three neutral species, Ar, O₂, and H₂O, are investigated by taking into account laser energy absorption due to inverse bremsstrahlung, ionization, attachment, diffusion, recombination, chemical reactions, and other possible physical processes. The laser intensity threshold is calculated from the balance between the initial electron gain (ionization) and the loss (diffusion and attachment). For argon the threshold intensity varies widely depending on the product of the neutral density and the diffusion length. For oxygen and water vapor, laser intensity higher than 10¹⁴Wm^-2 is necessary because ionization must exceed the loss due to attachment. Simulations are also conducted by taking into account the time variation of the laser intensity and the results show a reasonable agreement with the experimental results.