Design and fabrication of planar multilayer structures with coherent thermal emission characteristics

A large number of recent publications dealt with enhanced emission properties of micro/nanostructures by the excitation of surface plasmon or phonon polaritons. Some used grating structures to demonstrate coherent thermal emission in a narrow spectral band and towards a well-defined direction. Others suggested that planar layers could also be used to achieve coherent emission. In the present paper, we describe two alternative designs with fewer layers for the application as coherent emission sources in planar multilayer structures. One design is a composite of several unit cells of one-dimensional photonic crystal atop a highly reflective material. Coherent emission can be obtained by the excitation of surface waves between the photonic crystal and the reflector. The other design employs a Fabry-Pérot resonance cavity constructed by coating a dielectric layer onto the reflector and then a thin metallic film on the dielectric layer. When standing waves exist in the cavity, the emissivity plots show sharp spectral peaks and narrow angular lobes. By optimizing the film thicknesses, a close-to-unity emissivity can be achieved from the proposed structures. The theoretical predictions are supported by the measured spectral reflectance from fabricated samples.