Accurate measurements of thermal radiation from a tungsten photonic lattice

Recently, photonic lattice structures have become available that are fabricated from refractory materials such as tungsten and thus stable in vacuo at high temperatures. Such structures can be tailored to exhibit optical properties that are not achievable with ordinary optical materials. In particular, photonic lattices can be designed to suppress thermal emission in undesired spectral regions, and can thereby enhance the overall energy efficiency of emission at useful wavelengths. We report measurements of the thermal emission spectra of tungsten photonic lattices in the wavelength range 3 to 24 μm. Suppression of thermal emission at wavelengths longer than the photonic bandedge (∼6 μm) is observed, along with significant emission at shorter wavelengths. We show that from 404 to 546 K the spectral emissivity E(λ) is temperature independent and approaches [1-R(λ)], where R(λ) is the measured specular reflectance spectrum. These results are in accord with Kirchhoff's law