Investigation of laser drilling processing using Speckle Correlation techniques

Abstract: A method to study the response in materials exposed to high energy laser pulses has been developed in this thesis. The method is based on focused and defocused Speckle Correlation and uses an illumination cw laser and digital camera to acquire images of speckle patterns. These images were captured using a CCD camera before, during and after the laser drilling processing and were saved in a computer. All image processing was performed after the drilling process has been finished. By using this method the size of the affected zone, in-plane strain, surface tilt and surface deformations can be quantified with the temporal resolution limited by the frequency of the camera being used. This thesis comprises three papers. One conference paper was presented at the International Conference on Laser-Matter Interaction in St.Petersburg 2003, and two papers were submitted to Applied Optics. Results are shown from single shot interaction on sheets of Al2O3 and stainless steel as well as responses in sheets of copper and silver during percussion hole drilling. The results obtained during processing are also compared with SEM images. It is concluded that the method gives valuable information about the drilling process and that it is a robust and highly sensitive alternative to Interferometry for the study of laser-matter interaction processes.