Reading a CD that has no reflective layer

[Don Hills]

I think you're actually more likely to be able to read it in modern drives,
which are designed to handle lower reflectivity as found on burnt CD-R and
CD-R/W discs.

On Tue, Nov 18, 2014 at 9:51 AM, Mouse <mouse at rodents-montreal.org> wrote:

> > As I understand it, the depth of the pits are about a fifth of the
> > wavelength of the light used to read them, so the detector sees a
> > phase shift.
>
> I thought the pits were, in theory, 1/4 wavelength deep, so that the
> reflection from the pit is 180 degrees out of phase with the reflection
> from the surrounding area, producing destructive interference (ie,
> manifesting as a drop in reflectivity).  Of course, .25 is about .2....
>
> I don't understand why this technique was used.  Perhaps it's
> easier/cheaper to produce a nonsmooth surface made of a uniform
> material than to produce a smooth surface of a nonuniform material?
> (That's the other way I'd expect to produce reflectivity variations.)
>
> Is it possible that it's clear only in visible light, with some sort of
> reflective layer present in the (infrared, IIRC) wavelengths used?
>
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