>
>Anyone doing EME (earth moon earth) with light? Presumably
>a sufficiently narrow band optical filter and collimation would
>do the trick.


EME won't work at amateur power levels, even if you use the retroreflectors
left there on the surface. With kilowatt powered lasers, you only get a
couple hundred photons per second back. So, us civilian laser folks will
never get to do EME. Even at these power levels, ultranarrow field of views
are needed in the receiver optics, the receiver optics must be very large
very large collimators are needed. The large collimator makes a very tight
beamwidth on transmit, but this causes the shots at the retroreflector to
miss most of the time because the moon's libration becomes a problem then.
The large amount of ambient light from the moon's surface puts the final
nail in the EME coffin, at least for us civilian types.


>Per HOUR seems rather pointless though. Almost as bad a
>submarine communications using ULF radio.

It depends on your purpose. Several characters per hour is OK as long as
you don't want to transfer pictures or wav files:>: Seriously, the idea of
ultra narrow bandwidth receivers is to research and study tropospheric
bending, ducting and reflections to see if non-line of sight communications
is practical. For this purpose, we only need to put up a stable frequency
and then look for traces with the same frequency on the other end of the
path. It's a long term study, so we set the receiver up and then go to bed
and check out the stored data the next day at our leisure.

>Speaking of submarines, do they not now use laser communications
>from satellites to ultrasensitive optical detectors?

Unknown, but I did read that the military uses satellite based laser to
uplink and downlink from their unmanned surveillance aircraft.

Good luck.

Art

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