Metallic metasurface as a directional and monochromatic thermal emitter

摘要

Mid to far infrared is an important wavelength band for detection of substances. Incandescent sources are often used in infrared spectroscopy because they are simple and cost effective. They are however broadband and quasi isotropic. As a result, the total efficiency in a detection system is very poor. Yet it has been shown recently that thermal emission can be designed to be directional and/or monochromatic. To do so amounts to shape the emissivity. Any real thermal source is characterized by its emissivity, which gives the specific intensity of the source compared to the blackbody at the same temperature. The emissivity depends on the wavelength and the direction of emission and is related to the whole structure of the source (materials, geometry below the wavelength-scale...). Emissivity appears as a directional and chromatic filter for the blackbody radiation. Playing with materials and structure resonances, the emissivity can be designed to optimize the properties of an incandescent source. We will see how it is possible to optimize a plasmonic metasurface acting as an incandescent source, to make it directional and quasi monochromatic at a chosen wavelength. We will target a CO2 detection application to illustrate this topic.