Spectrally Broadband and Highly Directive Thermal Emission with Dual Polarization

We report a design concept to achieve broadband directive thermal emission with <i>dual polarization</i>. We theoretically demonstrate narrow angular selectivity within 5° over an 8 to 12 μm bandwidth for a range of emission angles. Additionally, we show that one can make emission angles distinct for different polarizations by tailoring the constituent optical modes. Throughout our theoretical analysis, we identify a new resonant mode, distinct from the Berreman mode, which has demonstrated broadband directive thermal emission for TM polarization. This new mode enables directive thermal emission for both polarizations. Based on the fundamental framework, we also report the design of a nanophotonic structure to validate the experimental feasibility of our findings.<br/>Engineering the directivity of thermal emission has profound implications in thermal applications such as energy conversion, thermal imaging, and radiative cooling. Achieving directive emission over a broad bandwidth is a challenging task requiring an independent control of the spatial and temporal coherence. While recent nanophotonic strategies have enabled broadband directive thermal emission for transverse magnetic (TM) polarization, achieving directivity for both TM and transverse electric (TE) polarizations remains elusive. To enhance the efficiency and versatility of thermal applications, it is important to directionally emit both polarizations over a broad spectral range.