Abstract
The absorption of incident laser beam is important when the quality of the laser machining is concerned, since the surface plasma acts as a medium between the workpiece and a laser beam. In the present study, the measurement of electron number density and temperature is carried out using a Langmuir probe. Effective absorption coefficients due to electron-ion and electron-neutral collisions as well as photoionization processes are dealt with analytically using the Maxwell's equations. The validity of classical treatment for the electron-neutral collision in relation to absorption is introduced and discussed. Consequently, the absorption coefficients due to these processes are computed within the frame of the data obtained from the present work. The study is extended to include the transmittance of He–Ne laser beam through the surface plasma generated during laser beam-workpiece interaction. It is found that the electron-ion collision is the dominant mechanism in the absorption process. The present data indicates that about 85% of the reference He–Ne is absorbed at the location close to the irradiated spot center in the plasma, therefore, the attenuation, scattering and deflection of the reference beam is mainly due to vapor atoms than the charged particles.