Carlo Rizza

Extreme nonlinear electrodynamics in metamaterials with very small linear dielectric permittivity

We consider a subwavelength periodic layered medium whose slabs are filled by arbitrary linear metamaterials and standard nonlinear Kerr media and show that the homogenized medium behaves as a Kerr medium whose parameters can assume values not available in standard materials. Exploiting such a parameter availability, we focus on the situation where the linear relative dielectric permittivity is very small, thus allowing the observation of the extreme nonlinear regime where the nonlinear polarization is comparable with or even greater than the linear part of the overall dielectric response. The behavior of the electromagnetic field in the extreme nonlinear regime is very peculiar and characterized by interesting features such as the transverse power flow reversing. In order to probe this regime, we consider a class of fields (transverse magnetic nonlinear guided waves) admitting full analytical description and show that these waves are allowed to propagate even in media with

Terahertz active spatial filtering through optically tunable hyperbolic metamaterials

\ensuremath{\epsilon}l0

Transmissivity directional hysteresis of a nonlinear metamaterial slab with very small linear permittivity.

and

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

\ensuremath{\mu}g0

All-optical active plasmonic devices with memory and power-switching functionalities based on {epsilon}-near-zero nonlinear metamaterials

since the nonlinear polarization produces a positive overall effective permittivity. The considered nonlinear waves exhibit, in addition to the mentioned features, a number of interesting properties like hyperfocusing induced by the phase difference between the field components.

Polariton excitation in epsilon-near-zero slabs: Transient trapping of slow light

We theoretically consider infrared-driven hyperbolic metamaterials able to spatially filter terahertz (THz) radiation. The metamaterial is a slab made of alternating semiconductor and dielectric layers whose homogenized uniaxial response, at THz frequencies, shows principal permittivities of different signs. The gap provided by metamaterial hyperbolic dispersion allows the slab to stop spatial frequencies within a bandwidth tunable by changing the infrared radiation intensity. We numerically prove the device functionality by resorting to full wave simulation coupled to the dynamics of charge carries photoexcited by infrared radiation in semiconductor layers.

Effective medium theory for Kapitza stratified media: diffractionless propagation.

We investigate propagation of a transverse magnetic field through a nonlinear metamaterial slab of subwavelength thickness and with a very small and negative linear dielectric permittivity. We prove that, for a given input intensity, the output intensity is a multivalued function of the field incidence angle so that the transmissivity exhibits angular multistability and a pronounced directional hysteresis behavior. The predicted directional hysteresis is a consequence of the fact that the linear and nonlinear contributions to the overall dielectric response can be comparable so that the electromagnetic matching conditions at the output slab boundary allow more than one field configuration within the slab to be compatible with the transmitted field.

|\epsilon|-Near-zero materials in the near-infrared

We have fabricated a nano-laminate by alternating metal and gain medium layers, the gain dielectric consisting of a polymer incorporating optically pumped dye molecules. From standard reflection-transmission experiments, we show that, at a visible wavelength, both the real and the imaginary parts of the permittivity e∥ attain very small values and we measure, at λ = 604 nm, |e∥|=0.04 which is 21.5% smaller than its value in the absence of optical pumping. Our investigation thus proves that a medium with a permittivity with very small modulus, a key condition promising efficient subwavelength optical steering, can be actually synthesized.

Optically induced metal-to-dielectric transition in Epsilon-Near-Zero metamaterials.

We theoretically propose and numerically investigate an active plasmonic device made up of a nonlinear {epsilon}-near-zero metamaterial slab of thickness smaller than 100 nm lying on a linear {epsilon}-near-zero metamaterial substrate. We predict that in free-space coupling configuration the system operating at low intensity displays plasmon mediated hysteresis behavior. The phase difference between the reflected and the incident optical waves turns out to be multivalued and dependent on the history of the excitation process. Such an hysteresis behavior allows the proposed system to be regarded as a memory device whose state is accessible by measuring either the mentioned phase difference or the power, which is multivalued as well, carried by the nonlinear plasmon wave. Since multiple plasmon powers comprise both positive and negative values, the device also operates as a switch of the plasmon power direction at each jump along an hysteresis loop.

Nonlocal homogenization theory in metamaterials: Effective electromagnetic spatial dispersion and artificial chirality

We numerically investigate the propagation of a spatially localized and quasi-monochromatic electromagnetic pulse through a slab with Lorentz dielectric response in the epsilon-near-zero regime, where the real part of the permittivity vanishes at the pulse carrier frequency. We show that the pulse is able to excite a set of virtual polariton modes supported by the slab, the excitation undergoing a generally slow damping due to absorption and radiation leakage. Our numerical and analytical approaches indicate that in its transient dynamics the electromagnetic field displays the very same enhancement of the field component perpendicular to the slab, as in the monochromatic regime. The transient trapping is inherently accompanied by a significantly reduced group velocity ensuing from the small dielectric permittivity, thus providing a novel platform for achieving control and manipulation of slow light.