Working of CD-R (Compact Disk – Recordable)

CD-R (Compact Disk – Recordable) are compact disks where data can be written to the disk by the user but only once. Here’s how a CD-R is made: 0.6 micrometer wide holes are made in a coated glass disk by using an infrared laser. For providing continuous feedback holes have sinusoidal excursion of 0.3 mm at a frequency of 22.05 kHz. This glass disk is used to make a mold and molten poly-carbonate resin is injected in to the holes. Then, a layer of dye of cyanine or thalocyanine is added on the poly-carbonate. After that a thin layer of reflective gold is deposited on the dye. It is then topped by a protective lacquer and at the top a label is put. For writing the CD-R, a high power laser is used. When the laser beam hits the dye, due to the chemical reaction a dark spot is created. When the CD-R is played the dark spots and the transparent areas are recognized.

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