3. Beam-substrate interactions and applications

Interactions between particles and surfaces can be of two kinds: elastic or inelastic.

Elastic interactions are of no interest for surface treatments, since no transformation can take place. They are therefore interactions to be limited leading instead to yield losses, as in the case of the reflection of laser beams on metal surfaces for example (over 90% reflected energy for a CO ₂ laser beam on a solid steel surface).

Inelastic interactions, on the other hand, lead to structural and/or compositional transformations of the treated material's surface zone. The following paragraphs will therefore describe possible applications as a function of the main parameters of the interaction, and in particular as a function of the power density at impact, a quantity that is often rather tricky to determine...