Observation of Thermal Beaming from Tungsten and Molybdenum Bull's Eyes

Abstract

Although losses in plasmonic films can be detrimental for optoelectronics, they can be exploited to create novel thermal emitters. Surface plasmon polaritons that are thermally excited on a heated metal surface can be converted to photons with useful properties. We demonstrate highly tailored thermal emission from tungsten and molybdenum films patterned with a series of circular concentric grooves (i.e., a bull's eye). At 900 degrees C our structures emit an infrared beam normal to the film that is spectrally narrow (tens of nanometers) and highly directional (similar to 2 degrees angular divergence). The peak wavelength (3.5 mu m) can be tuned with groove periodicity. To enhance the thermal stability of the structures, we add a thin layer of HfO2. Such devices, with their simple design and low thermal mass, provide interesting incandescent light sources for various applications.