Partially Spatial Coherent Thermal Emitter Based on an Epsilon-and-mu-near-zero Metamaterial

The accidental Dirac cone of a photonic crystal allows the realization of a low loss dielectric metamaterial with simultaneous near-zero effective permittivity and permeability. The resulting zero refractive index allowed applications that require unique spatial coherency. While most thermal light sources were considered highly incoherent, structurally engineered thermal emitters have achieved relatively high spatial coherency. Here, we propose an epsilon-and-mu-near-zero metamaterial as a spatial coherency converter for thermal emissions, and experimentally demonstrate surface-normal directional emissions with an angular width of 20 degrees.