Re: Solar powered lasers in space

On Sep 19, 11:38 am, IsaacKuo <mech...@xxxxxxxxx> wrote:
On Sep 19, 9:30 am, Willie.Moo...@xxxxxxxxx wrote:

Right. That's the point of the pilot beam from the target. You can
set it up so that a 'seed' beam as you called it, could be used as a
reference. Basic holography really - and that reference could direct
the energy to another point. But to my way of thinking a pilot beam
FROM the target is a simple solution.

A beam from the target won't provide useful phase information,
unless combined with other reference beams.

Correct - hence the name 4 wave mixing -

Holography
works only if the hologram in question is perfectly rigid to
within the wavelength divided by 4*sin(theta/2) (where theta is
the diffraction angle).

That is true -

With a pilot beam from the target,
this means the array must be rigid within 1/4 the wavelength.

No it does not.

But if the array is that rigid, then you really don't need the
pilot beam at all.

Wait a minute - you're getting lost in the details.

First, a hologram can be made by shining a reference beam through the
film, and then reflecting an object beam - split off from the
reference beam - that bounces back from the objects being imaged. You
can use very stable frames and optical tables and whatnot - especially
back in the day. That's what I did in my lab.. You can also use very
short exposure times in different venues - taking a hologram of a
person for example.

You can also take multiple 2D pictures of a scene and use them to
digitally compute a hologram that reproduces the image in 3D. .

But we're not making a picture of the target. We're merely
constructing a conjugate power wave in response to an incoming pilot
wave.

Think about it this way... You have a fabrey perot cell into which
you're pumping a gawdawful amount of solar energy from the sides to
energize some sort of lasing media. The media is sandwiched between a
semi-reflective mirror and a fully reflective mirror - producing a
continuous wave laser output. Fine. The laser beam is firing and
thats it.

Now replace the fully refletive mirror in the fabry-perot cell with a
phase conjugate mirror, and shine another laser into the apeture from
somewhere - and you will find that the solar pumped laser will return
energy to you. I've done this. It works. It has also been reported in
the literature.

Contrast this with a gabor zone plate lens, combined with
a far away "seed laser" drone behind the lens. In this case,
the diffraction angle is very nearly zero. Thus, the lens
does not need to be very rigid in order to efficiently
function. (A gabor zone plate is a hologram.)

I agree with everything you say. But I'm talking about using
holographic techniquest and nonlinear optical media to construct a
laser that returns a conjugate beam to a target multiplied many
thousands of times in energy - in response to a weak pilot beam..

You are avoiding that subject altogether. Since you seem
knowledgeable, let me give you some references you might find useful
Then maybe you'll understand what i'm getting at.

I'm talking about creating a optical phase conjugation system - not a
holographic imaging system. So, lets be clear about this. We want to
project energy from a large solar pumped laser - safely and reliably
to a large number of moving targets simultaneously though intervening
media with some measure of control. Nothing you have said suggests
this is not possible.

http://lapt.ece.northwestern.edu/pub/files/Efficient%20and%20fast%20optical%20phase%20conjugation.pdf

http://en.wikipedia.org/wiki/Four-wave_mixing
http://en.wikipedia.org/wiki/Nonlinear_optics
http://en.wikipedia.org/wiki/Self-focusing


If you use multiple reference beams, each in rigid formation
to within 1/4 wavelength, then it's possible to integrate the
beam information in a way to get perfect phase alignment
in any direction.

Yes, and that is done in the back plane of the fabrey perot cell by
the pilot beam.when it interacts with the phase conjugate mirror

This requires active processing, rather
than a passive hologram.

Correct. By active processing I presume you mean nonlinear optical
media that responds to both the pilot beam and the laser beam..

Isaac Kuo


.

Relevant Pages

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  • Re: Solar powered lasers in space
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    (sci.space.policy)
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