| 摘要 |
An optical system is described for use in processing information on a surface of an erasable record disc. The system decreases erasure time by forming an elongated spot from the generally circular cross section of a collimated laser beam so as to provide increased illumination time to an area recorded on the disc. The system includes a source of collimated light having a generally circular cross section, a cylindrical lens for focusing one aspect of the collimated light at a finite distance f, and a beam expander having the principal plane of its input lens at the distance f from the cylindrical lens, where the light forms a beam waist. An objective lens focuses the expanded elongated beam to a diffraction spot on the surface of the record disc. A linear actuator, such as a voice coil, responds to a control signal to position the cylindrical lens in the path of the collimated light beam for the erasing process, or out of the light path for the recording process.
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