Infrared thermal source or perfect absorber sensor based on silver 2D grating
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Infrared thermal source or perfect absorber sensor based on silver 2D grating Imed Sassi1 · Ridha Mghaieth1 Received: 19 May 2020 / Accepted: 25 July 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract We design and numerically investigate the spectral properties of two kinds of 2D Ag structured surfaces. The first structure is composed of Ag achieving a maximum absorption of 90% with the optimal structured parameters. The insertion of a metal layer between the grating layer and the substrate improved not only the absorption (greater than 95%) but also the sensor performance. Numerical computation is conducted to obtain the spectral distribution of powers with different structural parameters using the rigorous coupled-wave analysis method. Thus, we have demonstrated that any considered silver structure behaves either as a thermal source or a plasmonic sensor in the infrared range. The degree of directivity of each thermal source studied depends on several geometric and optical parameters. The best directivity is characterized by a narrow band of the full width at half maximum equal to 10.46 mrad with a nearly perfect absorption. Then, the performance of this source is identified by a quality factor (Q) equal to 176.52. The proposed structure as a perfect absorber sensor gives a maximum sensitivity of 4000 nm/RIU , a maximum absorption of 100% (demonstrated by strong fields distribution), and a maximum value of figure of merit equal to 52.71 RIU−1 for analyte refractive index ranging from 1.33 to 1.4. The proposed structures have great potential as biosensors. Keywords Plasmonics · Spectral properties · Thermal source · Perfect absorber sensor
1 Introduction Narrow band optical absorbents have a very wide field of application, such as thermal sources [1], photonic detectors [2, 3] and sensors [4, 5]. To obtain the narrow band absorption, we can adopt Fabry–Pérot’s cavities [6, 7], diffraction gratings [8–11] or even photonic crystals [12–14]. Based on Kirchhoff’s law, emissivity is equal to the absorbance of such a heat source [15]. So, to make a narrow band heat source, the absorbance term for a specific direction, wavelength and polarization has to be maximized. The structures based on surface Plasmon resonance (SPR) are widely examined to solve this problem. It has been shown that from materials supporting surface waves, we can obtain several SPR microstructures, with great spatial coherence manifested by very directional emission [16–20]. * Imed Sassi [email protected] 1
Laboratoire de Micro‑Optoélectronique et Nanostructures, Faculté des Sciences de Monastir, Université de Monastir, Monastir, Tunisie
The width of the narrow band of an angular emission lobe measures the directivity of such a thermal source. By an engraved grating, one can observe a directional emission, signature of spatial coherence [21]. This emission is of SPR origin, and has been observed for a grating of SiC [16, 17, 21, 22], Au [18] and W [20]. For example, the angular width of the emission lobe is 15
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