LG RHT497H Service Manual page 100

3) Recording format using phase-change recording material
(DVD-RW / DVD+RW)
Data is recorded by changing the recording layer from the amorphous status to the crystalline status, and
played back by reading the difference of the reflection coefficient.
Amorphous: Non-crystalline.
• Disc structure
• Recording principles
[ Recording ]
when a high-power laser is applied to the recording material, it melts and then becomes amorphous
with a low reflection coefficient when it quickly cools off. when a mid-power laser is applied to heat
gradually the recording material and then gradually cools it off, it becomes crystal with a high reflection
coefficient.
[ Playback ]
A low-power laser is used for playback. The amount of reflected light depends on the status (amorphous
or crystalline) of the recording material. This is detected by an optical sensor.
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