| 摘要 |
An optical information medium (20) for recording, such as DVR-blue, and a method for manufacturing such a medium (20) is provided. Reading from and recording onto the medium (20) is performed by means of a focused radiation beam (10) having a radiation wavelength & and a numerical aperture NA. Said medium has a substrate (1), and a stack (2) of layers provided thereon. The stack (2) comprises at least a first recording stack (3) and k radiation beam transmissive layers (4, 5). Each transmissive layer (4, 5) has a refractive index ni and an average thickness di mum and 1 = i = k and k = 2. The thickness dk of layer k (5) is determined by a simple formula which depends on the parameters ni for i & 1...k and di for i = 1... k-1. Such a medium (20) has zero or substantially zero spherical aberration at the focal point, being at the recording layer of the first recording stack (3), of said radiation beam (10). |
