Gain assisted nanocomposite multilayers with near zero permittivity modulus at visible frequencies

We have fabricated a layered nano-composite by alternating metal and gain medium layers, the gain dielectric consisting of a polymer incorporating optically pumped dye molecules. Exploiting an improved version of the effective medium theory, we have chosen the layers thicknesses for achieving a very small value of the real part of the permittivity epsilon_\| (parallel to the layers plane) at a prescribed visible wavelength. From standard reflection-transmission experiments on the optically pumped sample we show that, at a visible wavelength, both the real and the imaginary parts of the permittivity epsilon_\ attain very small values and we measure | \epsilon_\| | = 0.04 at lambda = 604 nm, amounting to a 21.5-percent decrease of the minimum | \epsilon_\| | in the absence of optical pumping. Our investigation thus proves that a medium with a dielectric permittivity with very small modulus, a key condition which should provide efficient subwavelength optical steering, can be actually synthesized.Comment: Submitted for publication on Applied Physics Letter

One-dimensional chirality: strong optical activity in epsilon-near-zero metamaterials

We suggest that electromagnetic chirality, generally displayed by 3D or 2D complex chiral structures, can occur in 1D patterned composites whose components are achiral. This feature is highly unexpected in a 1D system which is geometrically achiral since its mirror image can always be superposed onto it by a 180 deg rotation. We analytically evaluate from first principles the bi-anisotropic response of multilayered metamaterials and we show that the chiral tensor is not vanishing if the system is geometrically one-dimensional chiral, i.e. its mirror image can not be superposed onto it by using translations without resorting to rotations. As a signature of 1D chirality, we show that 1D chiral metamaterials support optical activity and we prove that this phenomenon undergoes a dramatic non-resonant enhancement in the epsilon-near-zero regime where the magneto-electric coupling can become dominant in the constitutive relations.Comment: 5 pages, 4 figures. Accepted for publication on Physical Review Letter