Design, manufacturing and test of a highly dynamic piezo-driven metal mirror for laser material processing

This paper reports on the opto-mechanical design and manufacturing of a highly dynamic piezo-driven metal mirror. This metal mirror replaces the last 90° deflecting mirror in conventional laser material processing heads. The central element of the mirror is a diamond turned free-form membrane. The membrane design is optimized to correct astigmatic aberrations which arise from the 90° beam deflection while simultaneously shifting the laser focus over a large range. In combination with a 200 mm focus lens, this allows diffraction-limited focus movements of up to 20 mm. A coating is applied to the mirror surface which has been successfully tested for cw laser loads up to 4 kW. The mirror is activated by a controlled piezoelectric stack actuator allowing beam oscillations up to 2.5 kilohertz. Optical, static and dynamic properties of a protoype mirror are characterized in order to qualify the mirror for laser cutting and welding processes.