On Fri, 11 Jan 2013 00:59:01 -0000, "Arfa Daily"
wrote:



"William Sommerwerck" wrote in message
...
This article says the DVD wavelength is 650nm, and calls it "red".

http://en.wikipedia.org/wiki/Optical_disc_drive

However, I find that a bit on the short side for red.


A 'standard' consumer DVD laser is bright red at around 650 nm wavelength. I
have never seen one tending towards amber, or indeed any shade of yellow. A
CD laser is infra red at around 780 nm wavelength. On the other hand, the
laser fitted to a Blu Ray DVD player is just that - blue - and has a much
shorter wavelength at just over 400 nm. The reason for each wavelength
becoming shorter as you go from CD to Blu ray, is that each disc type packs
more data on its playing surface(s) and it does this by using ever smaller
pits and lands. In order to resolve these, shorter and shorter wavelength
lasers are required ...

Arfa
And as demand for greater density increases we will find 'optical'
disc drives using increasingly shorter wavelength lasers - near UV,
extreme UV, X-Ray, Gamma ray...

PlainBill