METHOD OF MARKING A BODY OF MATERIAL

摘要

PCT No. PCT/GB94/01819 Sec. 371 Date Jul. 1, 1996 Sec. 102(e) Date Jul. 1, 1996 PCT Filed Aug. 19, 1994 PCT Pub. No. WO95/05286 PCT Pub. Date Feb. 23, 1995A method of providing a body of material (14), having a thermal conductivity approximately equal to that of glass, with a sub-surface mark. A beam of laser radiation (12) to which the material (14) is substantially opaque is directed to surface of the body, so as to cause beam energy to be aborbed at the surface of the material in an amount sufficient to produce localised stresses within the body (14) at a location spaced from the surface without any detectable change at the surface, the localised stresses thus produced being normally invisible to the naked eye but capable of being rendered visible under polarised light.