Bound and free waves in non-collinear second harmonic generation

We analyze the relationship between the bound and the free waves in the noncollinear SHG scheme, along with the vectorial conservation law for the different components arising when there are two pump beams impinging on the sample with two different incidence angles. The generated power is systematically investigated, by varying the polarization state of both fundamental beams, while absorption is included via the Herman and Hayden correction terms. The theoretical simulations, obtained for samples which are some coherence length thick show that the resulting polarization mapping is an useful tool to put in evidence the interference between bound and free waves, as well as the effect of absorption on the interference patternComment: 10 pages, 7 figure. to be published on Optics Expres

Hybrid thermal Yagi-Uda nanoantennas for directional and narrow band long-wavelength IR radiation sources

We investigate the possibility of spatially and spectrally controlling the thermal infrared emission by exploitation of the Yagi-Uda antenna design. Hybrid antennas composed of both SiC and Au rods are considered and the contributions of emission from all the elements, at a given equilibrium temperature, are taken into account. We show that the detrimental effect due to thermal emission from the not ideal parasitic elements drastically affect the performances of conventional thermal Au antennas in the 12 μm wavelength range. Nevertheless, our results show that the hybrid approach allows the development of efficient narrow-band and high directivity sources. The possibility of exploiting the Yagi-Uda design both in transmission and in reception modes, may open the way to the realization of miniaturized, efficient, robust and cheap sensor devices for mass-market applications. 2020 Optical Society of America

Optimization of thermochromic VO2-based structures with tunable thermal emissivity

In this paper we design and simulate VO2/metal multilayers to obtain a large tunability of the thermal emissivity of IR filters in the typical MWIR window of many infrared cameras. The multilayer structure is optimized to realise a low-emissivity filter at high temperatures useful for military purposes. The values of tunability found for VO2/metal multilayers are larger than the value for a single thick layer of VO2. Innovative SiO2/VO2 synthetic opals are also investigated to enhance the optical tunability by combining the properties of a 3D periodic structure and the specific optical properties of vanadium dioxide

Emissivity characterization of different stainless steel textiles in the infrared range

We experimentally investigated the infrared properties of a set of steel textiles, prepared using different type of fabrics. Infrared emission of the textiles was characterized in the mid-infrared range, i.e. 8÷14 mm, by observing their temperature evolution under heating regime with a focal plane array (FPA) infrared camera. Standard test method for measuring and compensating emissivity using infrared imaging radiometers was applied to the set of metallic textiles. The obtained experimental results allowed to retrieve the infrared emissivity at different applied temperatures. Although their infrared emission show some differences depending on the specific fabric, all the investigated textiles composed of steel yarns appear to be suitable for thermal shielding applications. Finally, the measured data were interpreted by means of the finite-difference time-domain (FDTD) numerical simulations as well as using Plank's theory of black-body radiation

Mapping the nonlinear optical susceptibility by noncollinear second harmonic generation

We present a method, based on noncollinear second harmonic generation, to evaluate the non-zero elements of the nonlinear optical susceptibility. At a fixed incidence angle, the generated signal is investigated by varying the polarization state of both fundamental beams. The resulting polarization charts allows to verify if Kleinman symmetry rules can be applied to a given material or to retrieve the absolute value of the nonlinear optical tensor terms, from a reference measurement. Experimental measurements obtained from Gallium Nitride layers are reported. The proposed method does not require an angular scan thus is useful when the generated signal is strongly affected by sample rotationComment: To appear on Opt. Let

Asymmetric transmission and anomalous refraction in metal nanowires metasurface

Here we investigated the asymmetric transmission and the anomalous refraction introduced by a metasurface of bent gold nanowires. The refraction follows the generalized Snell's law that takes into account the resonant behavior of metallic nanostructures located at the interface between two dielectrics. Measurements performed in the linear optical regime reveal a large sensitivity to the subwavelength features of the gold nanostructures

Optical polarization based logic functions (XOR or XNOR) with nonlinear Gallium nitride nanoslab

We present a scheme of XOR/XNOR logic gate, based on non phase-matched noncollinear second harmonic generation from a medium of suitable crystalline symmetry, Gallium nitride. The polarization of the noncollinear generated beam is a function of the polarization of both pump beams, thus we experimentally investigated all possible polarization combinations, evidencing that only some of them are allowed and that the nonlinear interaction of optical signals behaves as a polarization based XOR. The experimental results show the peculiarity of the nonlinear optical response associated with noncollinear excitation, and are explained using the expression for the effective second order optical nonlinearity in noncollinear scheme