INVESTIGATION INTO ABSORPTION OF THE INCIDENT LASER-BEAM DURING ND-YAG LASER PROCESSING OF METALS

Laser materials processing is highly affected by the existence of surf ace plasma. The absorption of surface plasma during drilling alters th e power intensity distribution of the incident laser beam across the i rradiated spot. The present study is carried out to measure the electr on number density and temperature using a Langmuir probe while a mathe matical formulation is conducted for the absorption coefficients due t o electron-ion, electron-neutral atom collisions, inverse Bremsstrahlu ng, and photoionization processes. Consequently, a computer program is developed to compute the relevant absorption coefficients as well as the overall absorption coefficient. The laser power intensity distribu tion before and after the plasma absorption is computed at a plane 2.6 mm above the workpiece surface, It is found that 13% of the reduction occurs in the incident laser output power intensity at this plane in the plasma. Copyright (C) 1996 Elsevier Science Ltd.