On Mon, 1 May 2006 16:03:57 -0500, "da pickle"
wrote:

(snip)

The problem is focusing the
heat ... normal glass is opaque at these wavelengths. You have to use
exotic metals as lenses. (For the big boys, you cannot use anything because
the heat eats your lens ... we build tiny tornados and actually bend the air
itself into a useable lens ... but we have already eliminated those guys.)
(I am omitting the problems with the rear reflectors which tend to get eaten
in the process as well ... damn things are a nuisance.)

So, we are left with electrical heaters and some sort of parabola lens
mechanism ... and try as I might, I cannot come up with anything that seems
reasonable to project to eight feet focused at six inches. That is a pretty
tight beam.
(snip)

I don't think so. Diffraction limit of a 6" dia aperture at 10
microns is well under a degree, while a 6" spot at 8 feet subtends
about 3.5 degrees. No harm in having the projected "spot" larger
than 6" dia.

The trick would be in getting a small enough source that is intense
enough to work. If your little parabola has a focal length of 6", the
image of the emitter would be magnified by about 16X at 8 feet. A
suitable emitter might be a small halogen bulb as used in a projector,
run at reduced voltage.

The reflector could be mae from a concave ladies' cosmetic mirror.
Drill a small hole in the center. Lay mirror on some gold-metallized
thin plastic film with superglue around the periphery. When glue has
set, trim around mirror, then squirt some superglue in the hole, shake
to distribute, then pull a vacuum to suck the film against the concave
surface.

I have a roll of such film somewhe gold on kynar or something. If
you email me I'll see if I can find it, and if I do I'd be glad to cut
you a foot square of it and mail it to you. I know I have some of it
wrapped around a minnow bucket, but that piece might be a bit
wrinkled.