We have demonstrated thermal emission of linearly polarized and narrow-band mid-infrared waves from sub-wavelength gratings of narrow and deep rectangular cavities engraved on a Au surface. 100-nm-wide and 1000-nm-deep, high-aspect-ratio trenches were accurately manufactured by inversion from master molds. Quarter-wave resonance of surface plasmons in the cavities exhibits a Lorentzian emission peak centered at 2.5—5.5 μm. The maximum emittance reaches 0.90, and the peak width Δλ/λ is as narrow as 0.13—0.23. Furthermore, we have demonstrated that orthogonally polarized two-color infrared waves can be emitted from a single Au surface by integrating orthogonal gratings with different dimensions. The integrated emitters were applied to non-dispersive infrared analysis for determining the concentration of a specific chemical compound in liquids.
