| 摘要 |
The invention concerns an optical detection system for retrieving information stored in a record track which effectively constitutes a sequence of light scattering or light deflecting elements. An objective lens, disposed above the record track, forms a reading spot for interrogating the track as it is moved past the spot. A photodetector, also disposed above the track, is located in the far field of the reading spot and outside the cone of focused light established by the lens in forming that spot to monitor the time-varying diffraction pattern of the spot reflected from the interrogated portion of the track. Upon receipt of scattered or reflected light rays, the photodetector derives an electrical signal representative of the stored information.
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