Adapting the axial focus in high-power laser processing machines within mm-range

The High-Power Focus Mirror we present in this paper gives access to dynamic focus position adaptation along 3.6 mm in high-power laser manufacturing. We developed and tested a new thermo-mechanical design for a unimorph deformable mirror that provides an extensive focal length range down to -2 m focal length. Moreover, the mirror’s unique thermal characteristics enable high-power applications up to 6.4 kW (2000 W/cm²) with stable optical beam quality as thermal lensing is successfully suppressed. Thus, the laser’s optical beam quality M² is stable over the entire actuation and thermal range. We will describe the design and the characterization of the High-Power Focus Mirror. The mirror setup is based on a unimorph concept using a piezoelectric actuator and a thin glass substrate with a highly reflective multilayer coating. An integrated copper layer improves the heat dissipation. Providing maximum stroke, as well as excellent dynamic properties, the deformable mirror substrate is mounted by our established compliant cylinders [1]. Furthermore, we investigate the incorporation of the High-Power Focus Mirror into a commercial laser-cutting system. We set up a laser-cutting test bench including a multimode laser source, the focus mirror, a commercial laser processing head, and measuring instruments. In this assembly, we measure the achievable focus position range as well as the laser beam quality. With this focus mirror, we want to encourage new, innovative high-power application fields in 3D laser processing such as laser cutting, welding, and structuring.