鉄のエキシマレーザ加工時に誘起されるプラズマの解析 エキシマレーザによるアブレーション加工の基礎的研究 （第１報）

Abstract

Emission spectra in KrF excimer laser induced plasma were measured with time resolution of the order of tens ns in laser materials processing of iron target; excitation temperature of the laser-induced plasma was determined by a Boltzmann plot of Fe (I), and electron density was determined from an intensity ratio of Fe(I) and Fe(II) lines. At a power density of 8×102 W/m2, the temperature and electron density were approximately 17000-18000 K and 5×1026 m-3 at the end of laser pulse of 30 ns, respectively. The absorption of KrF excimer laser was also measured in the laser induced plasma by using the probe laser beam travelling parallel to the target surface, which is split from the main KrF excimer laser. The absorption coefficient in the plasma thus obtained reached as high as approximetely 4×103 m-1 at the end of laser pulse duration. This value agreed well with the value calculated from the inverse-Bremsstrahlung theory when the excitation temperature and electron density obtained by the spectral method are used. This indicates that considerable amount of laser energy can be absorbed in the laser induced plasma without reaching the target via the absorption in the plasma at the later part of the laser pulse.