| 摘要 |
<p>A device is described for optically scanning two types of record carrier (1; 25) with a radiation beam (15) having a high numerical aperture. The radiation beam is focused through a transparent layer (2; 26) of the record carrier on an information layer (3; 27) by means of an objective lens (10) and a plano-convex lens (11). The magnifying power of the plano-convex lens is equal to 1/n1, i.e. the inverse of the refractive index of the transparent layer (2). The gap between the plano-convex lens and the record carrier can be maintained at a fixed value when the scanning is changed between the first and the second record carrier.</p> |
