Writing to a CD-R

image adapted from www.pctechguide.com		The CD-R starts out with a sheet of translucent dye, such as the cyan-blue coloured cyanin. When the write laser, which is much more powerful than the read laser, passes over the dye it fires bursts of intense light. These bursts cause the dye to heat up and the chemical composition changes to a light absorbing form. An opaque area that will absorb the light of the read laser is created. The dye is designed so that the read laser’s weaker beam will not cause the chemical to alter. The alteration must not require too much energy, so that the writer can perform its job quickly.
Once the dye has darkened it cannot be returned to the translucent phase and any data written to the disc is permanent. CD-Rs are therefore termed WORM (write-once-read-many) discs. After writing to the disc it can be read as often as required, as long as the disc itself is not damaged.