Posted by Andrew Rossmann on 12/24/06 15:55

[This followup was posted to rec.video.dvd.tech and a copy was sent to
the cited author.]

In article <emkr2n$c6u$1@luna.vcn.bc.ca>, t2k@vcn.bc.ca says...
> Regular DVDs and audio Cd's used red rays. And if we're now using
> blue-violet lasers (Blu-ray) to read and write DVDs and Cd's
> because it has a shorter wavelength, why not keep going a little
> further to say, purple laser?
>
> Would it be possible going beyond the visible (colour) spectrum
> into the ultra-violet (UV) and X-rays?

I assume in theory, yes. The practicality is producing the correct type
of lasers, and any issues with material degradation, especially as you
get into UV and higher. There is also the issue of just how small you
can reliably mass-produce discs with ever smaller pits and lands, and
the accuracy of the pickups. We will probably see them in the future as
technology advances.

There is also how close the laser is to the surface. Blu-Ray has the
reflective surface virtually at the bottom (DVD/HD-DVD are roughly in
the middle, and CD's at the top.) This makes them more sensitive to
scratches and dirt compared to the CD's that focus 'through' much of it
to the reflecive layer that is effectively on the far side of the disc.

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