Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: Light -photon "saturation"

On Fri, 22 Oct 1999, Ed Schweber wrote:

What if the substance were exposed to such an intense light that a
majority of its atoms were in an excited state? Would the substance then
become transparent to any additional light at this frequency?

Has (or could) something like this be done experimentally?

I think this is how "population inversion" in lasers works. Most
real-world laser media are fairly complex, but if we think in terms of a
simplified model, we'd have an absorbtive material which can be "pumped"
into a state where all the atoms are excited. In this state the material
stops being opaque. Then, since "stimulated emission" is in operation,
any light which passes through the material will be amplified, as if the
material has become a "negative absorber." Of course not all of the atoms
need to be excited in order for the material to become transparent. When
just as many atoms are awaiting "stimulation" as are awaiting "pumping",
the population is on the borderline and the material is transparent at
that frequency. (For every photon which gets absorbed, another photon
will trigger an emission in the same direction of propagation.) When even
more atoms are pumped up, the material becomes an amplifer, and any images
transmitted through it will become brighter than they were before (sort of
like an image-intensifier tube). Slap on some mirrors, and the thing
breaks into oscillation.

If it were possible to easily produce a population inversion in a thin
disk of glass, that glass would behave as an amplifier-window. But this
would only work at a single frequency. Therefor, dope the glass with
several different dye molecules. WIthout the pumping, you'd get normal
sunglasses with dark grey lenses. Pump them up, and you'd get "night
vision inverse-sunglasses" with a full color display. Or would the
polished glass surfaces accidentally create a laser, and the
sunglasses-wearer would perceive an incredibly bright point-source
hovering out at infinity? (Remember that parallel rays "look like" a
distant star-like object.)



((((((((((((((((((((( ( ( ( ( (O) ) ) ) ) )))))))))))))))))))))
William J. Beaty SCIENCE HOBBYIST website
billb@eskimo.com http://www.amasci.com
EE/programmer/sci-exhibits science projects, tesla, weird science
Seattle, WA 206-781-3320 freenrg-L taoshum-L vortex-L webhead-L