A laser beam model for high performance microdrilling

We have demonstrated the high performance of UV laser microdrilling in polymers. For instance hole diameter ∼30 μm and length up to 18 mm (aspect ratio 600) can be obtained for PET when the laser beam setup is finely adjusted. In this work we further present a model for the incident laser beam which includes the optical setup and the laser source parameters (power and divergence). We show that the final hole geometry can be expressed in term of the laser source characteristics and that the optical setup composed of 2 lenses (condenser and projector) and a circular mask has to match some of the features of the source. Provided this condition is fulfilled the way to better drilling performances is outlined and will serve of guidelines for future experiments. In particular low divergence laser source can be used for smaller diameter hole or deeper drilling. This means also that the optical setup used to pattern the laser beam must be specially designed and adjusted.