Cherenkov radiation permeability and formula_16 is the index of refraction of the material the charge particle moves through. Unlike fluorescence or emission spectra that have characteristic spectral peaks, Cherenkov radiation is continuous. Around the visible spectrum, the relative intensity per unit frequency is approximately proportional to the frequency. That is, higher frequencies (shorter wavelengths) are more intense in Cherenkov radiation. This is why visible Cherenkov radiation is observed to be brilliant blue. In fact, most Cherenkov radiation is in the ultraviolet spectrum—it is only with sufficiently accelerated charges that it even becomes visible; the sensitivity of the human eye peaks at green,
Negative refraction propagation direction of the light, thus the sign of "n" must be chosen to match the physical situation. The principal symptom of negative refraction is just that – light rays are refracted on the "same" side of the normal on entering the material, as indicated in the diagram, and by a suitably general form of Snell's law. Negative refraction Negative refraction is the name for an electromagnetic phenomenon where light rays are refracted at an interface in the reverse sense to that normally expected. Such an effect can be obtained using a metamaterial which has been designed to achieve a