Evolution of Laser Ablation Plume Measured by Self-Mixing Interferometry

Laser ablation is the basis of most of the laser micromachining processes. Depending on the pulse duration, wavelength, intensity of the beam, as well as the material type, material removal may occur in the form of vaporization, melt expulsion, or direct sublimation. Most commonly material removal is accompanied by a plume formation. The characteristics of the plume can be analyzed to assess the ablation performance. Non-invasive optical methods for the purpose can be further exploited in industrial laser micromachining applications, if opportunely designed and implemented. This work uses an interferometric approach to investigate the optical path changes induced by the ablation plume formed during the laser percussion drilling of different metallic and ceramic materials. A self-mixing interferometer is installed inline to a laser micromachining setup composed of a ns-pulsed green fiber laser.