The blue period of lasers
Author: Mr. Belvedere -
Date: 27-7-2002
A little science firstAs we all know, CD players and recorders read and write the CD's with the aid of a laser. Laser is short for: Light Amplification by Stimulated Emission of Radiation. See http://www.howstuffworks.com/laser1.htm for a complete explanation of what a laser actually is.
In a nutshell this means that high emitted energy gives radiation in the form of light, sort of like a lightbulb does. However laser light is very different than your average lightbulb. Laser comes in a straight direct beam and in only one wavelength (only red, only green, only blue etc). This wavelength is measured in nanometers and science uses the Greek letter Lamda (
) for this.
See http://www.howstuffworks.com/light2.htm for more information about wavelengths and light.
Because a laser is a very tiny and direct beam it is perfect to reflect the data written on a cd, because the data is long (over 3 miles!) but it is very small (about 5 microns).
(Picture courtesy of http://www.howstuffworks.com/cd2.htm)
The laser sends a beam towards the cd data and the beam gets reflected or not, thus resulting in high or low digital signal. To put it simple: If the reflected beam gets picked up by the receptor, it's a 1 ,if not.. it's a 0.
If you write data on a cd, the real laser power kicks in. It actually heats up a certain part of the cdrom surface, thus creating a physical 0 or 1 on the cdrom, which can later be read by your cd player. This will be explained more thoroughly later on (Pages 9 and 10).
The smaller the wavelength of a laser is, the smaller the beam can be. If the beam is smaller .. it can also read/write the same data using a smaller width (less than 1 micron!). So, on the same amount of surface, a laser with a smaller wavelength can read/write far more data on that surface than a laser with a bigger wavelength! And that's what Blu-Ray is! A laser with a smaller wavelength. Blue.
