MadSci Network: Physics
Query:

Re: Is there a paint that is invisible in daylight except with glasses?

Date: Mon Apr 30 11:39:06 2001
Posted By: Uncle Al Schwartz, Organic synthetic chemist
Area of science: Physics
ID: 988333322.Ph
Message:

Color?  COLOR!  How could you have something perceptible be imperceptible 
except as a changed signal-to-noise ratio with an optical absorption 
filter, much less have the whole thing be invisible from the start?  We 
know from absorption spectroscopy that pulling a small number from a big 
background is fraught with difficulties.  The proper philosophy of attack 
is that of fluorimetry, where even single photon emission detection is 
possible without too much angst because the signal is not part of the 
background.

Pulverize a polarizer, apply/incorporate the dust, then interrogate with a 
detector viewing through a rotating polarizer to modulate the signal out of 
random ambient noise.  Thin-layer dichroic schemes may give you frequency 
of response-selective detection as well.  Human vision is wholly 
insensitive to polarization.  Magnetic CD readers can sense microradian 
Faraday rotations.  Silver thiogallate (AgGaS2, J. Appl. Cryst. 33 126 
(2000)) with non-polar achiral tetragonal space group I-42d (#122), has 
immense optical rotatory power at visible wavelengths: 522/millimeter 
along [100] at 497.4 nm (reversed along [010].  Piece of cake - if you know 
where to cut the slices.  If you are into nanofabrication, look up 
"Brewster window" in http://www.google.com/

Go mark your playing cards, and buy a pair of Polaroid sunglasses.

How do you plan to counter inevitable Enviro-whiner petitions, marches, and 
lawsuits demanding that your government exercise jackbooted State 
compassion (and your tax monies) to Save the Bees! (Bees have a 
polarization jones for navigating.)  After all, who cares that the Spotted 
Owl is just as happy catching rats in a nice Home Depot lumberyard as in a 
dank decaying forest?

Uncle Al!


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