Andrea, I don't want anyone to think that I am pretending to have
a knowledge of physics, because I have almost none. I have stated
as much in other threads. Paul has many charts and equations in
his book that I know little of, and don't have the computer skills
to post. For instance, one of the shorter comments under one chart
is as follows: "Relative spectral radiance of nitrogen at 22 Torr
(closely approximating one millimeter of mercury) excited by 10 keV
electrons. The effective spectral slit width was 18A (the A had a little
o above it, I assume it had to do with angstroms) and the total scanning time approximately 90 minutes. Below 3200A the relative intensity is less certain." He offers summaries sometimes for the
non-physicist, which I sometimes understand.
Another paragraph
devoted to the non-physicist, I assume, is the following:
"The quantum mechanical explaination for the indistinct or invisible
outline of the UFO at night is particularly straightforward. In excited molecules, the downward drop of the electron through various energy levels is a reversible process. When two molecules each have an
electron in an unstable upper energy level u, that drop to a lower level 1, they each give off a photon with an energy equal to the difference in the energy levels u and 1. If the photon from the first molecule properly encounters the second, it puts the electron right back from level 1 to level u, the reverse of the relaxation process.
This is why the spectroscopist says that the absorption spectrum
of a gas is equal to its emission spectrum. Any wavelength which
a gas emits it can, and does, absorb. Since the excited air emits in the visible wavelengths, it absorbs the same wavelengths, and there is a critical distance of a few feet of plasma that will absorb
the passing light. In other words, beyond a few feet of thickness
a plasma is essentially opaque to light of its own emission frequencies." I can't post the whole chapter, but maybe this will
be of benefit if it pertains to your question. I don't know if experiments have been performed, but he does have some stuff
about using lasars to simulate colors and effects.