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

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.