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Old June 1st 17, 07:16 PM posted to rec.arts.sf.science,sci.space.policy,sci.optics,sci.physics,sci.military.naval
Robert Clark[_5_]
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Posts: 245
Default Reusable Laser Launcher

"Robert Clark" wrote in message news ================================================== ==========
We now have the capability to do laser launch. The problem is the initial
cost outlay for the lasers is still prohibitive to launch a sizable payload.

But is it possible to do it without using lasers, just high intensity
noncoherent light focused by mirrors or lenses?

I wondered about this because of two reports I saw doing a web search
actually on optical communication:

InfiniLED MicroLEDs achieve 300 W/cm2 output density from tiny source.
The MicroLEDs semiconductor manufacturing process includes construction of a
parabolic reflector to enable optimal light control and high efficiency from
micro-meter-sized LEDs.
Published on:Jan 29, 2013
By Maury Wright
http://www.ledsmagazine.com/articles...ny-source.html

and:

Optical communications using coherent and non-coherent light.
http://modulatedlight.org/optical_co...cal_about.html

The first report discusses micro-scale LED's whose light output scales up to
300 W per square centimeter, 3 megawatts per meter. From the appearance of
these micro-scale LED's, they should permit simple automated production to
produce many copies to cover a macro-scale area to generate light even at
gigawatt power levels.

The second report discusses experimentation that suggests atmospheric
dispersion is actually worse for lasers than for noncoherent light generated
by LED's. See for instance the video in Fig. 2 on this page.

The advantage of the lasers however is that generating a parallel beam, you
can use a parabolic mirror to focus the light at the focal point (more
precisely at the Airy disk). Still, nevertheless a parabolic mirror will
still focus a large portion of the light at the focal point even for
noncoherent light.

So the question is if the beam is noncoherent, how much of the light can
still be focused at the focal point (Airy disk)?


Bob Clark
================================================== ==========

On another discussion forum it was pointed out I missed a key fact in that
article on the InfiniLED MicroLEDs:

InfiniLED MicroLEDs achieve 300 W/cm2 output density from tiny source.
Quote:
The MicroLED is built using an LED semiconductor structure and can be
driven like standard LEDs. But the manufacturing process, which includes
etching of a parabolic reflector at the semiconductor level, delivers a
collimated beam like a laser (see the parabolic structure in the nearby
photo). The result is both high-intensity light and high efficiency.
"This device can be seen as a cross-over between the power and collimation
of a laser and the simplicity of an LED. The unique devices enable a range
of applications," said chief commercial officer of InfiniLED, Bill Henry.
"InfiniLED are proud to have achieved the landmark performance of optical
density greater than 300 W/cm2. This was achieved without the need for
external optics indicating the potential for further improvement of the
performance."
http://www.ledsmagazine.com/articles...ny-source.html

The key fact I missed is that the light produced by the MicroLED is
*collimated*. This means the light rays are parallel. But this is what is
needed for the light to be focused to a point (Airy disk) using a parabolic
mirror. It doesn't really need to be coherent like a laser. Not actually
having to make a laser inherently makes it a simpler and cheaper system.

So this may mean the question is moot about how much a parabolic mirror can
focus when using incoherent light. However, we will need to array many
copies of the MicroLED's to create a large beam. But when the pattern is
repeated, likely the degree of collimation will be degraded somewhat over
the entire size of the array. That needs to be determined.

Still, even if there is a lack of collimation over a large array, we can
produce a collimated beam from it from optical elements called collimators:

Collimated light.
https://en.wikipedia.org/wiki/Collimated_light

Another possible advantage of just using LED's rather than going for a laser
is that LED's can have high efficiency, as much as 80%, though the
efficiency of the InfiniLED's isn't specified.


Bob Clark

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