Shadowgraphic and interferometric investigations on Nd : YAG laser-inducedvapor/plasma plumes for different processing wavelengths

Shadowgraphic and interferometric images of vapor/plasma plumes generated b y pulses of a ns-Nd:YAG laser reveal the distinctive behavior of the shock wave expansion for each of three processing wavelengths (1064 nm, 532 nm, a nd 355 nm), indicating that different mechanisms dominate the interaction b etween the optical fields and the material vapor/plasma. Electron density d istributions within the plasma plumes calculated from interferometrically o btained refractive index distributions allow us to describe the regions of absorption and the absorption mechanisms using a simple model of inverse br emsstrahlung and photoionization, which allows us to estimate absorption co efficients.