Using Reflected Light as a Measure of Best Focus and Control Variable in an Ablation-Focused Optical System

We use a femtosecond laser with a high numerical aperture to ablate precise sections of a metallized polymer for various purposes. For best performance, the focus of the laser must always remain as close to the surface as possible. Here we detail a control system that uses the light reflected from the metallized surface to ensure the focus remains within 1.77 micrometers of the surface, resulting in uniform ablation behavior across a relatively large area of the sample. We achieved an ablated metal-mesh filter with 86% accuracy on the first pass with this approach.