Surface waves between metallic films and truncated photonic crystals observed with reflectance spectroscopy

Thermal radiation transferred to the guided modes of optical interference coatings

An electromagnetic model is developed to predict the thermal radiation which is trapped in a multilayer structure and transferred to its guided modes. The theory is based on the electromagnetic power supplied by the thermal currents given by the fluctuation-dissipation theorem. The source of the radiation is the ambient temperature or that caused by the optical absorption of the component subjected to spatio-temporal illumination. A numerical example is given for a multi-dielectric mirror at thermodynamic equilibrium. It is shown that the thermal radiation transferred to the guided modes of the multilayer can be much larger or lower than the radiation emerging in free space outside the component.

Photo-induced thermal radiation of optical interference coatings submitted to a spatio-temporal illumination

We present an electromagnetic model for photo-induced thermal radiation in multi-layer interference filters subjected to arbitrary pulsed illumination with limited beam size. Numerical calculation is used to analyze various structures affecting thermal radiation, such as multi-dielectric mirrors in the mid-infrared range. Other zero-admittance structures are shown to strongly confine and enhance the thermal radiation with an emissivity close to unity at pre-defined frequencies (wavelength and angles). Calculation tools are chosen that encourage the use of techniques for synthesizing thin-film multilayers able to control thermal radiation.

Nearly perfect resonant absorption and coherent thermal emission by hBN-based photonic crystals

In this paper, we numerically demonstrate mid-IR nearly perfect resonant absorption and coherent thermal emission for both polarizations and wide angular region using multilayer designs of unpatterned films of hexagonal boron nitride (hBN). In these optimized structures, the films of hBN are transferred onto a Ge spacer layer on top of a one-dimensional photonic crystal (1D PC) composed of alternating layers of KBr and Ge. According to the perfect agreements between our analytical and numerical results, we discover that the mentioned optical characteristic of the hBN-based 1D PCs is due to a strong coupling between localized photonic modes supported by the PC and the phononic modes of hBN films. These coupled modes are referred as Tamm phonons. Moreover, our findings prove that the resonant absorptions can be red- or blue-shifted by changing the thickness of hBN and the spacer layer. The obtained results in this paper are beneficial for designing coherent thermal sources, light absorbers, and sensors operating within 6.2 μm to 7.3 μm in a wide angular range and both polarizations. The planar and lithography free nature of this multilayer design is a prominent factor that makes it a large scale compatible design.

Coherent thermal emission by excitation of magnetic polaritons between periodic strips and a metallic film

The present paper theoretically demonstrates coherent thermal emission in the infrared region by exciting magnetic polaritons between metallic gratings and an opaque metallic film, separated by a dielectric spacer. The coupling of the metallic strips and the film induces a magnetic response that is characterized by a negative permeability and positive permittivity. On the other hand, the metallic film intrinsically exhibits a negative permittivity and positive permeability in the near infrared. This artificial structure is equivalent to a pair of single-negative materials. By exciting surface magnetic polaritons, large emissivity peaks can be achieved at the resonance frequencies and are almost independent of the emission angle. The resonance frequency of the magnetic response can be predicted by an analogy to an inductor and capacitor circuit. The proposed structure can be easily constructed using micro/nanofabrication.