Re: [ATM] Infrared Considerations

[David Weinshenker <daze39@earthlink.net>]

I suppose you could go even further down the frequency band and 
approach a millimeter-wave radio telescope: a smooth sheet-metal 
or aluminized plexiglass dish can be a high-resolution primary 
reflector at 300 GHz or so, and the focal plane becomes an array
of miniature dipole antennas on a printed circuit or integrated
circuit substrate...

-dave w


Richard Schwartz wrote:
> 
> 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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