|MadSci Network: Physics|
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  at 497.4 nm (reversed along . 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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