Diamond slicing using ultrashort laser-induced graphitization and additional nanosecond laser illumination

Single-crystal diamonds exhibit properties consistent with semiconductor substrates. However, they are hard and brittle, making them difficult to slice. Therefore, this study demonstrates diamond slicing by applying femtosecond laser internal processing, which converts diamond to graphite. Additionally, the use of nanosecond lasers for further modification is also demonstrated. This method enables diamond slicing with only a small kerf loss. A femtosecond laser beam (pulse energy of 2 μJ, pulse duration of 550 fs) was tightly focused using an objective lens with a numerical aperture (NA) of 0.5. The focus was scanned parallel to the optical axis towards the light source (i.e., backward). The scanning speed was set to 100 μm/s. A continuous modified line of 12–15 μm diameter was formed in the diamond. In addition, adjacent single lines were formed with a spacing of 5 μm, and a planar modified layer (15–20 μm thick) was generated in the bulk diamond. The differences in crystal orientation in the texture of the modified layer were also clarified. In addition, the first modified layer was reheated using a nanosecond pulsed laser to convert it into a separable layer. A diamond of size approximately 1 × 1 mm2 was separated, and the separated surface and cross section were observed. Furthermore, the separation of the diamond depended on a crack generated in the front of the modified layer during additional laser illumination. Raman spectroscopy showed that the modified layer contained graphite.