In-process monitoring in laser grooving with line-shaped femtosecond pulses using optical coherence tomography

A line-shaped beam is useful for increasing the processing speed in laser grooving and scribing. In laser grooving, depth control of the processed structure is important for performing precise processing. In this paper, in-process monitoring of the depth of a structure formed by femtosecond laser processing with a line-shaped beam using swept-source optical coherence tomography (SS-OCT) was demonstrated. In the evaluation of the SS-OCT system, the depth resolution, measurement accuracy, and axial measurable range were 15.8 μm, ±2.5 μm and 5.3 mm, respectively. In laser grooving, the structural shape and the distribution of deposited debris were successfully monitored. The measured depth agreed well with the depth obtained using a laser confocal microscope. The proposed method will be effective for precise laser processing with feedback control of the laser parameters based on in-process monitoring of the processed structure.