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English to Japanese translations [PRO] Tech/Engineering
English term or phrase:mark
An additional advantage of optical discs is the absence of physical contact between the reading head and the information layer because of the existing simple ways to focus radiation in the optical region of the electromagnetic spectrum.
A transparent film covering the information may even protect the fine details from damage and from shadowing particles.
As in a conventional gramophone record the information is stored in a spiral,
called the track, though in many cases neither a groove nor a continuous line is present but only marks forming a spiralling broken line.
The marks are small areas showing optical contrast with respect to the surrounding mirror surface, for example black line-shaped elements or oblong depressions (pits) in the surface.
This causes the reflection to change along the track according to the marks.
The optical pick-up which replaces the mechanical stylus of the gramophone converts the variation of the reflection into an electrical signal.
The lens of the pick-up focuses a laser beam to a small spot of light on the track and sends the light reflected off the disc to a photodetector.
The photo signal thus varies in time according to the marks along the track of the rotating disc.