Negative Refractive Index in a Plasma Induced by Laser

Summary form only given. In a previous research the authors demonstrated that a layer of cold, weakly-ionized gas surrounds the plasma produced by a focused laser. This layer is like a halo or corona that contains a population of free electrons that make the layer behave like a conductor. It was also found that this layer has a thickness of 2-3 mm. The mechanism by which this outer layer is ionized is by UV light from the plasma; in addition, some of the free electrons produced by the focused laser beam may drift to the outer layer. An experiment was devised that consisted in shining a pulse of green light (fiducial) from an Nd:YAG laser through the outer layer of the plasma produced by focusing the IR light from the same source. The two components were separated by means of a frequency-doubler and a separator. The light emitted from the plasma and the fiducial was simultaneously registered by a streak camera with a resolution better than 100 ps. For times close to the plasma onset and energies well above threshold, it was found that when the fiducial passes through the outer layer it is deflected towards the plasma. Calculations of the refractive index using classic plasma formulae predict a deflection away from the plasma. For this reason the observed deflection in this case is attributed to a negative refractive index. A plasma with its diamagnetic properties and its conductor-like behavior complies with the requirements of a left-handed medium that has a negative index