Radiative Transfer in Pulsed-Laser-lnduced Plasma

Abstract

When a high-power pulsed laser interacts with materials, a plasma layer containing micrometer-size particles is formed above the target surface. The laser induced plasma changes the energy coupling mechanism between the laser beam and the target. This work investigates the radiative heat transfer process in the excimer laser generated plasma layer on the Ni specimen, in the laser fluence range between 1.5 and 5 J/cm2. Novel diagnostic techniques are developed to measure transient transmission and scattering of the thin plasma layer within the duration of the laser pulse. Based on the measurement results, radiative heat transfer analysis is performed to evaluate the radiative properties of the plasma layer, including the optical depth, the absorption coefficient, the single scattering phase function, and the scattering size parameters. Knowledge of the radiative properties of the laser induced plasma helps to understand the energy transfer process during laser-materials interaction. Further, this work demonstrates the feasibility of using the transient scattering measurement for in situ monitoring of the size of the laser ejected particles.