Interaction mechanisms of pulsed laser beams at different wavelengths with matter

Sammanfattning: This thesis presents an investigation of the interaction mechanism involved in processing of different engineering materials using pulsed TEA CO2- and Nd:YAG lasers. Several methods were used. Digital Speckle Photography (DSP) or Speckle Correlation was used to detect micro-structural changes in the material surface during laser irradiation. Scanning Electron Microscopy (SEM) and optical microscopy were used to obtain information about hole quality; entrance and exit diameters, amount of spatter, cracking etc., when laser drilling. Optimum processing parameters, for example wavelength, pulse repetition frequency and pulse energy were established and are presented in this thesis. In Papers A and B, an evaluation of the interaction mechanism using Digital Speckle Photography (DSP) is presented. Paper C focuses more on the influence of the laser irradiation parameters on the quality of laser drilled holes. To find optimum processing parameters, SEM and optical microscopic investigations of thermoplastic polymers, and thermoset polymers exposed to laser irradiation with different wavelengths were carried out. Thermoplastics PMMA and Polycarbonate and a thermoset epoxy matrix reinforced by glass and graphite fibres were used. The results from the first paper showed that microstructural changes caused by laser pulse impact can be visualised. The results of other two papers showed that, for hole drilling, short wavelengths are most suitable since these give good hole quality in most engineering materials including metals and composites.