Spectral Control of Thermal Radiation by Metallic Surface Relief Gratings
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1162-J03-01
Spectral Control of Thermal Radiation by Metallic Surface Relief Gratings Hitoshi Sai1, Yoshiaki Kanamori2, Kengo Watanabe2, and Hiroo Yugami2 Research Center for Photovoltaics (RCPV), National Institute of Advanced Industrial Science and Technology (AIST), Central 2, 1-1-1 Umezono, Tsukuba, Ibaraki, 305-8568, Japan. 2 Graduate School of Engineering, Tohoku University, Aoba 6-6-01, Aramaki, Aobo-ku, Sendai, 980-8579, Japan. 1
ABSTRACT The microcavity effect of two-dimensional W surface-relief gratings has been investigated by means of the finite-difference time-domain simulation. The peak structure of the spectral emissivity of W gratings with a number of microcavities is in good agreement with the spectral features of a single microcavity. This result shows that the emissivity enhancement by W gratings with microcavities is mainly attributable to the microcavity effect that arises from each microcavity. It is that the spectral emissivity can be controlled by a combination of several microcavities with different parameters, and that not only a rectangular but a cylindrical microcavity also shows the microcavity effect according to its cavity modes. INTRODUCTION Recently, tuning the thermal radiation spectrum by introducing surface gratings has been of interest because it has a potential to offer various spectral properties by changing the surface design and materials. Since Hesketh et al. [1-4] found anomalous features on the spectral emissivity of Si lamellar gratings, many researchers have been studied on thermal radiation from surface gratings. In recent reports, it has been found that metallic or dielectric gratings exhibit several emission peaks at certain wavelengths, and that the peak wavelengths and the spectral profile can be controlled by changing the grating parameters [5-18]. In addition to surface gratings, thermal radiation control by photonic crystals has been reported by several groups [19,20]. The spectral control of thermal emission is attractive to develop various thermally radiative devices, e.g., a high-efficiency incandescent lamp [21] and a spectrally selective radiator for thermophotovoltaic generation [22]. In those applications, it is required to realize a spectral emissivity that is high in the visible (VIS) or the near infrared (NIR) region and low in the infrared (IR) region simultaneously. Surface gratings made from refractory metals are one of the promising options, because of their superiorly high melting temperature. Since metals generally have a quite low emissivity from the VIS to the IR regions, it is necessary to enhance the emissivity only in the VIS and NIR regions to develop such devices. In the case of metallic gratings, it was reported that several peaks were observed on their emission spectra when their periodicity comparable to the wavelengths of light [5-18]. Those emission peaks are supposed to be categorized into two groups by their origins, namely, surface plasmon polaritons (SPP) [5-10,16-18] and the microcavity effect [10-13,16]. SPP are the quantized c
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