Super-directive beam from metamaterials

In a quasi-zero-average-refractive-index (QZAI) metamaterial, the light scattered out is extremely directive (Delta theta(out) = 0.06 degrees), in despite of a divergent source at near infrared wavelength (lambda=1.55 mm). In this paper we discuss and experimentally demonstrate that this is possible when the light is coupled with diffraction order of a grating with alternating complementary media. The experimental data prove with a high degree of accuracy also the strong vertical confinement of the beam even in the air region of the metamaterial, where any simple vertical confinement mechanism is absent. This extremely sensitive device works on a large contact area and open news perspective to integrated spectroscopy.