Investigation of cw and ultrashort pulse laser irradiation of powder surfaces: a comparative study

Abstract

The paper presents results obtained in a comparative study of laser irradiation of tungsten powder surfaces using a continuous wave fiber laser and a high repetition rate femtosecond laser. Depending on the energy input per unit length different melt structures have been produced. In general, if the same average laser power level was applied the structures show the same appearance independent from the laser source. But there was both a little higher degree of initial fusing and cross-linking along the processed path when the powder surface was irradiated with ultrashort pulses. Further, with increasing laser intensity a change in structure formation as well as a broadening of the laser processed path has been occurred, although the energy input per unit length remains constant. However, accumulation of slab-like structures, which was previously observed in high-intense ultrashort pulse laser irradiation, has been become more pronounced in cw laser irradiation above a certain number of consecutive scans. Moreover, characteristic effects, such as formation of ripples and nanomelt structures appearing in ultrashort pulse laser processing have been not detected in cw laser irradiation.