Nature provides infinite number of substances with amazing properties. That is why scientists go back from time to time to learn from nature. The design of solar cells may benefit a great deal from inspecting how a plant makes food via photo-induced chemical reactions. What underlies the colorful butterfly wings is at all a marvelous texture, which is now known as photonic crystals. Nevertheless, sometimes the nature seems wanting in its diversity. An example is the so-called negative refraction materials (NRM), which are up to now not available naturally. All known NRM are made artificially, going under the name 'composite left-handed meta-materials'.
NRM is special in that, it has a negative refractive index, which means the refracted ray will lie on the same side as the incident ray, relative to the normal of the interface. This property stimulates novel ways of light manipulation. Many application are bound to take place. Years ago[1], it was utilized to make perfect lens, which has a remarkable resolution that is smaller than light wavelength, an impossible thing with conventional positive refraction materials. More innovations will surely come out soon.
Again due to this negative refraction, Cherenkov radiation will also be quite different. Actually, it is the reversed CR that happens. Namely, as a charged particle passes through an NRM dielectric at a speed greater than the light speed in this dielectric, backward radiation will be experienced. A direct experimental observation of this is much rare. In Ref.[2], a vivid simulation, however, was conducted. Despite this, it is still highly desirable to observe what will happen if a real beam is passed through the NRM.
A question: can we someday find a naturally available NRM ? This would be very interesting and exciting ... ...
[1]PRL, 85:3966(2000)
[2]PRL, 103:194801(2009)
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