We present optimized aperiodic structures for use as broadband, broad-angle thermal emitters which are capable of drastically increasing the efficiency of tungsten lightbulbs. These aperiodic multilayer structures designed with alternating layers of tungsten and air or tungsten and silicon carbide on top of a tungsten substrate exhibit broadband emittance peaked around the center of the visible wavelength range. We investigate the properties of these structures for use as lightbulb filaments, and compare their performance with conventional lightbulbs. We find that these structures greatly enhance the emittance over the visible wavelength range, while also increasing the overall efficiency of the bulb.
Bulk thermal emittance sources possess incoherent, isotropic, and broadband radiation spectra that vary from
material to material. However, these radiation spectra can be drastically altered by modifying the geometry of
the structures. In particular, several approaches have been proposed to achieve narrowband, highly directional
thermal emittance based on photonic crystals, gratings, textured metal surfaces, metamaterials, and shock waves
propagating through a crystal. Here we present optimized aperiodic structures for use as narrowband, highly
directional thermal infrared emitters for both TE and TM polarizations. One-dimensional layered structures
without texturing are preferable to more complex two- and three-dimensional structures because of the relative
ease and low cost of fabrication. These aperiodic multilayer structures designed with alternating layers of silicon
and silica on top of a semi-infinite tungsten substrate exhibit extremely high emittance peaked around the
wavelength at which the structures are optimized. Structures were designed by a genetic optimization algorithm
coupled to a transfer matrix code which computed thermal emittance. First, we investigate the properties of the
genetic-algorithm optimized aperiodic structures and compare them to a previously proposed resonant cavity
design. Second, we investigate a structure optimized to operate at the Wien wavelength corresponding to a
near-maximum operating temperature for the materials used in the aperiodic structure. Finally, we present a
structure that exhibits nearly monochromatic and highly directional emittance for both TE and TM polarizations
at the frequency of one of the molecular resonances of carbon monoxide (CO); hence, the design is suitable for
a detector of CO via absorption spectroscopy.
We explore an approach to enhance the efficiency of solar cells using photonic nanostructures for solar ther-mophotovoltaics. Our focus is on designing photonic nanostructures that can provide broadband absorption in a narrow angular range for solar thermophotovoltaic systems which do not employ sunlight concentration. We consider structures consisting of an aperiodic multilayer stack of alternating layers of silicon and silica on top of a thick tungsten layer. The layer thicknesses are optimized to maximize the angular selectivity in the absorp-tivity for both TE and TM polarizations. Using such an approach, we design structures with highly directional absorptivity for both polarizations.