[ATM] Infrared Considerations

["Richard Schwartz" <richard1941@gmail.com>]

There are great discoveries waiting for us in the infrared.   IR
observations can be done as easily during daylight as at night.
Imagine a 24 hour watch on a star to detect an eclipse and discover a
new planet!   But there are a few problems.

1. The atmospheric water vapor blocks IR except for a gap around 10
microns.   You need a high dry mountaintop if you are going to observe
outside of the 10 micron window.

2.  At 10 microns, the photons don't have enough poop to knock
electrons loose in semiconductors, so ordinary camera type focal
planes won't work.

3. The alternate focal planes, microbolometer arrays, start at about
$30,000.  The other alternate is SQUID devices... and they require
liquid helium cooling (but can also provide spectral information).

4. If you are not in a big hurry to get measurements, you can use a
single microbolometer.   This simplifies telescope design: you can
ignore coma.  In fact, a mirror with 3 waves of error for visible
light (a very rotten mirror) is fine for infrared.  I guess large
mirrors will be preferred.

Strong's book tells how to make a bolometer.  It involves stretching
wires incredibly thin by placing them inside a glass tube that is
heated and stretched.   This is not stuff for the faint of heart.
Arrays would be more difficult.
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