Cutting tool and cutting method

A cutting method comprising:

• providing a cutting tool for cutting a hard brittle material, the cutting tool being made of a commercially-available square diamond prism, and providing the square diamond prism of the cutting tool with a rake angle;
• propagating laser light from a laser light source through an optical fiber to a convergence lens and then into and through the cutting tool, and bringing the cutting tool and the hard brittle material into contact with each other to irradiate, with the laser light, at least a contact part of the cutting tool where the cutting tool and the hard brittle material are in contact with each other and a rake angle part of the cutting tool where the rake angle is provided;
• irradiating the hard brittle material through the contact part and the rake angle part with the laser light propagated through the cutting tool except for Fresnel reflection light reflected on an end surface of the cutting tool to soften the hard brittle material;
• and
• cutting the softened hard brittle material,
• wherein the laser light, which is propagated through the cutting tool except for the Fresnel reflection light reflected on the end surface of the cutting tool, is incident, through the contact part and the rake angle part, to the hard brittle material perpendicularly to a planar direction of a surface of the hard brittle material that is in contact with the cutting tool.