Demonstration of thermal emission control

In this paper, we describe our efforts to control the thermal emission from a surface utilizing structured surfaces with metal/dielectric interfaces. The goal was not to eliminate the emission, but to control the output direction and spectrum. We focus on methods that lead to high emissivity at grazing angles, with low emission near normal. We describe the fabrication and measurement of large passive devices (15×15 mm) and arrays of smaller chips for thermal emission control in the longwave infrared (8 to 12 micron) spectral region. All the devices consist of a metal base layer covered with dielectric/metal posts or lines, 0.5 microns tall. The posts (0.9×0.9 micron) and lines (0.3 micron wide) are subwavelength. One-dimensional and two-dimensional devices with a 3 micron pitch will be shown. The devices are measured with both a hemispherical directional reflectometer and a variable angle directional emissometer. Both simulated and experimental results show the thermal emission effectively limited to a small spectral region and grazing angles from the surface (≥ 80°) in stark contrast to the typical Lambertian radiation seen from unstructured material. Finally, the effect of this thermal emission control is illustrated using an infrared camera.