Observation of crack propagation and stress distribution in diamond induced by ultrashort-pulsed laser illumination

Ultrashort-pulsed laser illumination focused inside a diamond converts sp³-bonded diamond to sp²-bonded amorphous carbon in the vicinity of the focal point and changes the color to black. A wire-shaped modified region is fabricated by scanning the laser focus toward the laser source in the diamond. Volumetric expansion by converting diamond to amorphous carbon forms cracks around the modified region. In this study, diamond slicing was attempted by using cracks formed around the modified region. A near-infrared picosecond laser was focused inside a high-temperature, high-pressure diamond. The cracks fabricated under various laser conditions were observed. The plane crack was formed by lining up the wire-shaped modified regions next to each one. During the fabrication, a high-speed polarization camera was used to observe the stress distribution around the modified region and in the adjacent wire-shaped modified region. The crack propagation was estimated by observing the stress distribution in situ. The kerf loss in the slicing process was estimated by observing the cross section of the cracks from multiple directions. These results demonstrate that plane cracks suitable for slicing the diamond were fabricated. Diamond separation was performed by applying an external force to the plane cracks.