Real time active aiming?( was Re: [Laser] Laser comm stuff)

[J. Forster]

Derek Weston wrote:

> "J. Forster" wrote:
> >
> > If a retro was co-located with each receiver, tracking would be possible without
> > tracking data transfers.
>
> True, but even with a 100% effective retro relector, range with
> autoalign would be half the link's potential range.

Not necessarily. The tracking signal can be integrated (smaller BW) so a lower S/N
would work fine.

> Then again, perhaps the bandwidth of the modulation of the alignment
> signal could be much lower than that of the modulation for the data, so
> lower received levels during alignment than during data transfer could
> be OK in some cases.
>
> It'd be interesting to experiment using one of the precision retro
> reflectors used by surveyors.  Does anyone have an idea of the % of
> incident light these return and the typical angular difference between
> incident and returned beams?

At a guess 80%+. They are coated on the front face and have pretty good mirror
coatings. That's what I had in mind. The angle is an arc-second or two, at most.  You
could position 3 around your aperture. Similar items are available surplus.

Another possible solution would be to introduce a partial mirror (with a hole for the
detector light, or partially silvered) to reflect in your telescope's optical path.
This is much harder to align, though, since you need to tweak one end, then the other,
and iterate.

-John


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