SUPERLUMINALITY AND PARELECTRICITY - THE AMMONIA MASER REVISITED

It is well known that the inversion of populations in the ammonia maser leads to stimulated emission, and hence amplification, of microwaves. However, it is not well known that an inverted medium also leads to the superluminal propagation of off-resonance, finite-band-width nave packets, whose phase, group, energy, and ''signal'' velocities, as defined by Sommerfeld and Brillouin, all exceed the vacuum speed of light c. Einstein causality is not violated, since the front velocity is c. The inversion of populations also implies a parelectric medium with negative electric. susceptibility. (Parelectric media should not be confused with paraelectric media, which are ferroelectrics just above their Curie points.) The existence of a parelectric medium implies the possibility of the levitation of an electrical charge in the vacuum above this medium, as well as stable electrostatic configurations of charges placed inside an evacuated cavity surrounded by this medium. The apparent violation of Earnshaw's theorem will be discussed. Numerical estimates for a proposed experiment to observe parelectricity will be given.