‘‘Clean’’ processing of polymers and smoothing of ceramics by pulsed laser melting

Surface stability during laser pulsed melting of polymers and ceramics is studied theoretically. Irradiation conditions and material parameters are found giving rise to the suppression of surface wavy relief of a nonresonant type (with period Λ≫λ, where λ is the radiation wavelength) and thus to the smooth flat irradiation spots. For example, for the polymers considered this process takes place for wavelengths where the absorption coefficient is sufficiently high: α(λ)≳105 cm−1. Thus, it is shown that the formation of such spots, previously referred to as ‘‘clean ablation,’’ can be explained using only a thermal mechanism without reference to the concept of ‘‘photodecomposition.’’ Moreover, laser smoothing and polishing of a surface, if it had roughness before irradiation, can be achieved by appropriate matching of the characteristic size of this roughness along the surface with the values of α(λ) and laser fluence. Methods are proposed to decrease the parasitic influence of droplets on the deposition of thin films by laser ablation of massive ceramic pellets. The results of theoretical modeling are shown to be in good agreement with experiments on smoothing of rough alumina ceramics and ‘‘clean’’ processing of polymers by excimer laser radiation.