The mid-infrared (mid-IR), as the spectral range where all finite temperature biological and mechanical objects
emit thermal radiation, and where numerous molecular species have strong vibrational absorption resonances,
is of significant importance for both security and sensing applications. The design of materials with engineered
absorption resonances, which by Kirchoff’s Law, should give strongly selective emission at the design resonance
upon thermal excitation, allows for the control of the spectral character of the material’s thermal emission.
Designed as a thin film coating, these structures can be applied to grey-body emitters to shift the grey-body
thermal emission into predetermined spectral bands, altering their appearance on a thermal imaging system.
Here we demonstrate strongly selective mid-infrared absorption and thermal emission from three classes of subwavelength
thin-film materials. First, we demonstrate selective thermal emission from patterned, commerciallyavailable
steel films, via selective out-coupling of thermally-excited surface modes. Subsequently, we show nearperfect
absorption (and strongly selective thermal emission) for wavelengths between 5 - 9μm with patterned
metal-dielectric-metal structures. Finally, we demonstrate strong absorption from large area, unpatterned, thinfilm
high-index dielectric coatings on highly-doped Si substrates, tunable across the mid-IR (5 - 12μm). Our
results are compared to numerical simulations, as well as analytical models, with good agreement between
experiments and models.