"Lostgallifreyan" wrote in message
. ..

"Wayne" wrote in :

There is no loss due to distance itself, but to the radiation spreading.


I'm wondering now if what Gareth is concerned with is the same as divergence
in an asperic lens output with a laser diode. Assuming the diode has an
emitter width of a very few microns (is already usually only one micron in
one axis even in a multimode diode with a single 'stripe' emitter pattern)
then a large enough single asperic lens will make a finely directed but
broad
beam, but if you want it very narrow as well, it diverges more widely and
various optic methods will tame it a bit, but there's no real substitute for
a single mode diode if possible to use one for the wanted power.

Assuming it is NOT possible, the multimode diode needed will demand a bigger
lens to match its power efficiently into a well directed, 'collimated' beam.
It seems to me that this is more than just an analogy, but maybe
fundmentally
similar to the difficulties with energy density, accuracy of form, low loss
of materials used, aperture size for emission, and maybe several other
things
I've seen mentioned recently about this subject of small antennas. Including
the fact that eben if the laser beam IS highly divergent, the small aspheric
lens is just as efficnt at prjecting the power as the larger one, so long as
all light from the diode gets coupled through it without spill or
reflection.

I hope that's not too off-topic, but it seems to be that I might get some
learning from responses to this one...
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Well, it may be slightly off topic and certainly out of my field of
experience, but I find it more interesting than Gareth's misused equations