Measurements of the negative refractive index of sub-diffraction waves propagating in an indefinite permittivity medium

An indefinite permittivity medium (IPM) has been fabricated and optically characterized in mid-infrared spectral range (10.7 mu m-11.3 mu m). Phase and amplitude transmission measurements reveal two remarkable properties of IPMs: (i) transmission of sub-diffraction waves (as short as lambda/4) can exceed those of diffraction-limited ones, and (ii) sub-diffraction waves can propagate with negative refractive index. We describe a novel double-detector optical technique relying on the interference between subdiffraction and diffraction-limited waves for accurate measurement of the transmission amplitude and phase of the former. (C) 2010 Optical Society of America