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Re: bleaching



At 05:56 AM 10/22/99 -0400, Ed Schweber wrote:
I am starting by accepting the model that a substance's lack of
transparency is due to the absorbtion of photons.

Good!

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?

Absolutely. It's called bleaching.

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

It is done every day. See e.g.
http://materialscience.uoregon.edu/pslas.htm
which says in part:

Laser pump/probe techniques have become the preferred means for
performing time-resolved measurements in a broad range of fields,
including chemistry, physics, materials science, and biophysics. No
longer limited to traditional transient absorption/bleach measurements,
pump/probe measurements now encompass such diverse techniques as ...

Given a material with an assortment of absorbers, you can selectively
bleach one frequency and not others, leaving a remarkable absorption
spectrum with a notch in it.

Depending on details, the material might not *stay* bleached for very long.
The timescale might be set by the physics of re-radiation or
thermalization, or it might be set by chemistry (since the excited state
might be reactive).

See the recently-announced prize
http://www.nobel.se/announcement-99/chemistry99.html
if you're interested in the chemistry tangent.

______________________________________________________________
copyright (C) 1999 John S. Denker jsd@monmouth.com