CO₂ laser-plume interaction in materials processing

In laser materials processing, localized evaporation caused by focused laser radiation results in a partially-ionized plume above the material surface. The beam is refracted and absorbed as it traverses the plume and these effects are of interest for process development. Here, plume-beam interactions are studied using an axisymmetric, high-temperature gasdynamic model of a plume formed by vapor from a flat iron surface. The beam propagation in the plume is calculated from the paraxial wave equation including absorption and refraction. It is shown that absorption of the beam in the plume has much less direct effect on the power density at the material surface than refraction does. Helium gas is more efficient than argon for reducing the beam refraction and absorption effects. Laser energy reflected from the material surface has significant effects on the plume properties.