[Laser] Non-Imaging Optics

[Thomas Upton]

Mentioning again that there is no power loss when the optical filter is a diffraction
grating tilted to the frequency desired.  "You want red, you get red", but the rest
of the visible or invisible spectrum is still there in a spectrograph within the
collector.

So other wavelengths should be recovered by putting their particular  receiving
element at that portion of the "rainbow" created by the diffraction grating.

When the collecting element is a concave mirror, there is no difference in the focal
distance of wavelengths.  Unlike lenses, which bend different wavelengths in
proportion to the interaction of the lens and the medium in which it resides.

Incidentally, when the collecting element is a convex mirror, the light can become
polarized when the mirror is convex in one direction and not in another.  For
example, note the light off of a windshield; the sunlight is polarized because it is
convex in one plane and not in the other.

When that windshield light comes down a dark corridor onto a wall at the end of the
corridor, you can see the heat rising off of your hand or a cup of coffee, as well as
the cold rising from other sources.  You can even see your own breath, or the
moisture rising from your hand.  Very Interesting!
.
Tom Upton  AD6N

J. Forster wrote:

> Bob Williams wrote:
>
> >Has anybody tried using just a light-bucket approach for receiving diffuse light
> from atmospheric scattering - forward scatter, cloudbounce, etc...?
>
> >With images on the horizon, I think that light interference might make it
> pointless.
>
> You can eliminate much of the interference with a narrow band optical filter on
> your receiver, tuned to your transmitter's wavelength.
>
> -John
>
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