Development of in-process monitoring technique in YAG laser welding

We have studied in-process monitoring technique in Nd:YAG laser welding. We used a CCD camera and a photodiode as the monitoring sensor, and observed laser processing coaxially with the laser beam. There were differences in the image of the CCD camera between full and partial penetration welding and the detection for full and partial welding was achieved by the image processing of the detected image data. And, it was suggested that a change in the focal position could be detected because a change in the luminescence intensity could be caught with the photodiode when the deviation of the focal position occurred.