How Does a Laser Burn a DVD?
Like compact discs and other digital media, DVDs store data in binary code, a series of 1s and 0s that contains all the information necessary to reproduce a song or a video or a movie. Binary code is the same language that computers use to interpret and execute their programming; it's the bits and bytes that make all computer technology possible.
Writing and Reading Lasers
At its most basic, binary code tells a system to either be on (1) or off (0). On a DVD or CD, binary code is marked by either the presence or absence of reflective areas on the recording surface. A reflective area, if present, reflects the reading laser of a DVD player to an optical sensor, which records a 1 in binary. Absence of a reflective surface results in no light reaching the optical sensor and therefore the recording of a binary 0.
It's the job of the DVD burner to put these tiny reflective areas on the DVD's recording surface. It does this by using a writing laser. More powerful than the reading laser, which simply bounces light off the DVD, the writing laser actually darkens the surface of the DVD where it hits, creating a nonreflective surface that will later be read as a binary 0.
With the exception of the laser's strength, the interior of a DVD burner is fairly similar to a DVD reader. In both cases, the DVD must be spinning as the laser moves outward from the center. In the DVD burner, however, the laser is marking the recording surface of the disc with the series of 1s and 0s representing the data being recorded. Where the laser hits the DVD, a dark spot, a 0, is recorded. The laser shuts off and passes over areas intended to be reflective. In the DVD reader, these areas will reflect the reading laser onto the optical scanner and register a 1.
The process of creating rewritable discs does not differ from the procedure described above. What's different is the material used for the recording surface of a rewritable disc. Rewritable discs use heat-sensitive phase-change compounds that do not create permanently darkened areas when struck by the writing laser. Instead, the atoms of the materials rearrange their structure and change phases--that is, become more fluid than solid. The fluid form of the materials absorb light and are registered as 0s by a DVD reader. However, by passing the writing laser over the same surface, the phase of the materials can be changed again, resulting in a rewritable disc.