There are also continuous processes such as free-free absorption
and black body emission that can in principle give arbitrarily
low energy (long wavelength) photons.
But to examine very small things, you want small wavelength (high
energy) photons. These can be dangerous and destructive so
perhaps that is the reason for electron microscopes.
Jason
---------------------------------------------------------------------
Dept. of Physics and Astronomy University of Calgary
jmcvean@acs.ucalgary.ca http://www.ucalgary.ca/~jmcvean
"I am as close to you as the veins in your neck when I say to you, in
my whispering lisp, I, too, began as a boy." Mark Richard - Fishboy
---------------------------------------------------------------------