Single-lens dynamic z-scanning for simultaneous in situ position detection and laser processing focus control

Abstract

Existing auto-focusing methods in laser processing typically include two independent modules, one for surface detection and another for z-axis adjustment. The latter is mostly implemented by mechanical z stage motion, which is up to three orders of magnitude slower than the lateral processing speed. To alleviate this processing bottleneck, we developed a single-lens approach, using only one high-speed z-scanning optical element, to accomplish both in situ surface detection and focus control quasi-simultaneously in a dual-beam setup. The probing beam scans the surface along the z-axis continuously, and its reflection is detected by a set of confocal optics. Based on the temporal response of the detected signal, we have developed and experimentally demonstrated a dynamic surface detection method at 140–350 kHz, with a controlled detection range, high repeatability, and minimum linearity error of 1.10%. Sequentially, by synchronizing at a corresponding oscillation phase of the z-scanning lens, the fabrication beam is directed to the probed z position for precise focus alignment. Overall, our approach provides instantaneous surface tracking by collecting position information and executing focal control both at 140–350 kHz, which significantly accelerates the axial alignment process and offers great potential for enhancing the speed of advanced manufacturing processes in three-dimensional space.