Multibeam Micro-Drilling with High-Power Ultrashort Laser Pulses: 2-Stage Beam-Splitting Strategy and Implementation

In this paper, we describe a 2-stage laser beam-splitting strategy based on both polarization refractive and diffractive optics, and its implementation into independent modules. In the first stage, only refractive polarization optics is used and a variable number of sub-beams is produced, each sent to a different processing unit. The second stage, based on diffractive optics, splits further the sub-beams before they enter into the laser processing heads. Each resulting bundle of beamlets is then focused on the workpiece through a single focusing lens. We present the modules developed from this approach, the technical challenges involved and different practical ways to address them. One of these challenges is handling a high-power ultrashort laser radiation and hence, thermal regulation and potential damages to the system need to be considered. We discuss the implementation of the developed beam splitting units into a prototype with a kilowatt femtosecond laser, used to drill micro-holes in large Titanium metal sheets for an aeronautical application.