Femtosecond laser micromachining with extended depth of focus by using diffractive lenses

We show that a simple diffraction focusing element can alleviate mechanical tolerances in ultrafast laser microprocessing. In particular, we experimentally demonstrate that, in comparison with a conventional refractive lens (RL), focusing light pulses of 30 fs onto a stainless steel sample with a diffractive lens (DL) can increase twice the useful axial ablation region. This is thanks to the combination of the broadband spectrum of ultrashort pulses, and the huge longitudinal chromatic aberration associated with DLs. We believe that our results might be useful for reducing the complexity and cost of ultrafast microprocessing systems.