Measurement of laser beam transmittance through laser produced vapour plume

Laser produced plume, consisting of vapor front and ejected substrate on th e workpiece surface, is an intermediate between the incident laser beam and the workpiece on which the beam is directed. It partially blocks, defocuse s, absorbs, scatters, and deflects the incident beam and thereby reduces th e laser energy reaching the workpiece. However, plume additionally acts as a heat source enhancing the machining. Consequently, laser induced plume pl ays an important role in laser machining process, The present study investi gates the transmittance of a reference beam by the plume generated during t he laser-workpiece interaction. To achieve the transmittance measurements, a Nd:YAG laser was used and four different materials were employed in the e xperiment. To obtain realistic values of the plume transmittance in relatio n to the laser machining process, the reference beam was sampled from the i ncident laser beam. The study was extended to include the effect of the las er pulse parameters on the transmission process. It is found that about 10- 30% of the transmittance of the reference beam through a vapor plume. produ ced due to laser ablation, occurs close to the workpiece surface.