| 摘要 |
A birefringence measuring apparatus 30 measures a birefringence of a transparent substrate D1 of an optical disc D having a reflective layer D2 thereon by detecting a reflected light beam L2, which is a reflection of a light beam L1 from the disc. The light beam irradiates the disc at an incident angle of " alpha ", penetrates the transparent substrate, and reflected by the reflective layer. The light beam emitted from a light source 1 has a coherence length shorter than an optical path length P which is a sum of optical paths P1 and P2. The optical path P1 is a distance from the surface of the transparent substrate to the reflective layer, and the optical path P2 is a distance from the reflective layer to the surface of the transparent substrate. <IMAGE> |
