Low-Directivity Quasi-Monochromatic Thermal Radiation From Microcavities Covered by Thin Metal Film

Here, closed-end microcavity is proposed in which a semi-transparent metal film was formed atop microcavity. The structure shows weak angular dependence as well as quasi-monochromatic absorptance. Au is employed as material of the cavity walls and the covering thin film. Quasi-monochromatic absorption from the structure is observed in numerical simulation. High quality factor (Q factor) is obtained by strong confinement in the closed-end microcavity. Asymmetric and quasi-monochromatic absorption band with a Q factor of ∼28 at 1.85 μm was observed. This value was about 4-fold larger than that of the open-end microcavity. Additionally, the closed-end microcavity structure filled with SiO₂ in cavity exhibits isotropic and quasi-monochromatic thermal radiation over a wide solid angle. This result suggests that both quasi-monochromatic and low-directivity absorptance can be realized by using this configuration.