Spatial and temporal coherence of thermal radiation in asymmetric Fabry–Perot resonance cavities

There has been an increased interest on the development of micro/nanostructures with desired radiative properties for energy conversion systems and radiative cooling devices. A detailed experimental study is reported on the spatial and temporal coherence of thermal radiation in asymmetric Fabry–Perot resonance cavities. The reflectance of the fabricated samples was measured for both polarizations using a Fourier-transform infrared spectrometer, at several incident angles in the near-infrared region, and a laser scatterometer at the wavelength of 891 nm. The spectral measurement demonstrates sharp reflectance dips, while narrow angular lobes are observed in the angle-resolved measurement. Experimental results suggest strong spectral and directional selectivity in thermal emission, which is related to the reflection by Kirchhoff’s law since the samples are opaque. Theoretical calculations with the fitting geometric parameters agree well with the measurement results. This easy-to-fabricate structure has potential applications in solar cells, thermophotovoltaic devices, and radiation emitters.