Qualification of an Automatic Laser Beam Focus Monitoring Implemented on a New Ultrashort Pulsed Laser Robot System

We report on an automatic laser beam focus monitoring approach for an ultrashort pulsed laser robot system.The system integrates an ultrashort laser mounted on a link of a six-axis industrial articulated robot with a galvanometer scanner and an F-Theta lens mounted on the end of the last robot axis.This enables high precision micromachining using ultrashort pulsed laser over a large 3D processing area.A beam focus monitoring and adjustment method combining a distance sensor and cameras ensures consistent processing quality during extensive robot movement.A conventional beam focus monitoring algorithm based on image processing is compared with a deep learning-based method using YOLO object detection network, where a high accuracy is particularly observed using YOLO network-based method.In addition, the methods are implemented in the system and utilized for the beam focus monitoring for an ablation process of fused silica, with varying the processing surface orientations.Both methods demonstrate the capability for a correct beam focus detecting with surface orientations ranging from -30º to 15º, while maintaining the beam propagating axis parallel to the surface normal.