Plasma characterization in laser cutting

Characterization of a blue plasma was conducted using a high- speed I.I. video camera, a color CCD video camera, and a spectrum multi-channel analyzer. A blight blue plasma, which contains Fe, N2 and N2+ was observed from a cutting point in laser cutting with either through- and non- through penetration when the cutting quality was not satisfactory. From the results, a use of the blue plasma signals can be effective for the in-process monitoring of a cut surface quality in laser cutting. Also, removal processes of molten material, can be divided into two types, (1) by the dynamic pressure of a coaxial gas jet, and (2) by the recoil force with an evaporation. An explosive evaporation of molten material from a point of laser irradiation was observed almost simultaneously with the plasma formation. At the cutting front, a small crater was seen at a point of the plasma formation. It was found that N2+ and N2 spectra are not emitted directly through a direct absorption of a laser beam by a gas jet, but presumably through the secondary collisions of N2 in a gas jet with electrons and/or Fe atoms emitted and accelerated from the material surface by a strong radiant energy of the laser beam.