Reading a CD that has no reflective layer

[drlegendre .]

Slap a layer of Mylar on the back and give it a shot..? Might even work
with something of lower reflectivity, like white paper..

On Mon, Nov 17, 2014 at 5:57 PM, Don Hills <dmhills at gmail.com> wrote:

> 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?
> >
> > /~\ The ASCII                             Mouse
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>