Writable and Rewritable CD’s By Thomas Szychowski

The CD Written from inside out TOC is written first Last two mm left open Three types – Pressed – CD-R – CD-RW

Pressed CD Data is pressed on an aluminum layer Physical Pits and Lands Data is seen through the transition from one depth to another

Differences from Pressed and “burned” CDs Pressed – Metallic layer with different heights Burned – Everything is generally at the same height – Reflection is manipulated using lasers to create differences – Compounds are dyes that are responsive to localized heat

CD-R CD – Recordable Data kept on an organic dye compound – Normally reflective Laser “burns” areas in the die to represent a bump – Heats the dye to a critical point to change the materials properties – Burned areas are far less reflective than non-burned ones Permanent and irreversible

CD-RW CD – Rewritable Phase changing data layer Data is kept on a special combination of antimony, indium, silver and tellurium – Reflective originally Three laser powers – Read power Lowest power setting – Erase power More powerful than Read-power Sets the compound from Dull back to original state when cooled – Write power most powerful Creates a non-reflected area – Heated area is non-crystalline when cooled

Laser Power – CD-R cyanine dye – 6.5 mW at burn-speed of 1x – Faster burn speed means more powerful laser. Phthalocyanine – Alternative to cyanine dye – Excellent longevity – Lower powered laser at 1x – 5.5mW

Laser Power – CD-RW Power levels – Read State Low power – Low enough to not affect the chemical compound – Erase State Medium power – Temperature is below the melting point, but above the crystalline temp (~200ºC) – Atoms revert to crystalline form – Write State Highest power – Temperature rises to 500ºC to 700ºC – creates an amorphous state

Questions ?