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Narrow-Band Thermal Radiation with Low Directivity by Resonant Modes inside Tungsten Microcavities

Narrow-band thermal radiation with low directivity is presented using a periodic array of microcavities on tungsten surfaces. Thermally excited resonant modes inside the microcavities are found to enhance thermal radiation at specific wavelengths. Compared with a flat tungsten surface, thermal radiation from the microcavities has been enhanced by ∼200% at the most enhanced wavelength of λ=5.5 µm. This strong enhancement yields narrow-band thermal radiation with a full width at half maximum of Δλ=0.59 µm. The enhancement peak positions are well explained using a simple cavity resonator model. By measuring thermal radiation at oblique directions, it is also found that this narrow-band radiation has low directivity.