Optical characteristics of a two-dimensional dielectric photonic crystal immersed in a coherent atomic gas

We studied the specular and nonspecular remittances and the absorptance of two-dimensional photonic crystals (PCs) comprising a periodic array of dielectric rods immersed in a coherent atomic gas (CAG). Illumination by obliquely incident, s-polarized plane waves was considered. Minipassbands that may include peaks of nearly complete transmission appear within the stop bands of the corresponding gas-free PCs, due to the strong frequency dispersion in the relative permittivity of the CAG. As a result, high-efficiency passbands of a gas-free PC and those arising due to the CAG can coexist. The latter can be tuned in a simpler way than by varying the constitutive parameters of the CAG, i.e., via variation of the incidence angle. In contrast with the earlier studied metallic PCs immersed in a CAG, new passbands may also appear when the CAG behaves as a medium with ultralow positive permittivity. Also, complete absorptance bands (with zero overall reflectance and overall transmittance) can be obtained, which are well correlated with the frequency-dependent characteristics of the CAG.