Does anyone have any more information on the following (I haven't looked yet)?
Subluminal Cherenkov radiation. In vacuum, nothing travels faster than light. In transparent substances like water, however, it is possible for high-energy charged particles to exceed the speed of a light beam in that substance. When this happens, the particle will radiate a cone of light called Cherenkov radiation. A team of researchers (University of Michigan and Max Planck Institute for Condensed Matter Research in Stuttgart) has now taken a closer look at the theory, and found that conical Cherenkov emission also occurs at subluminal speeds. The researchers verified the finding experimentally using subpicosecond laser pulses to generate--through a nonlinear optical process--relativistic dipoles that emitted infrared Cherenkov radiation in a zinc selenide crystal. (T. E. Stevens et al., Science 291, 627, 2001.) --pfs
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