Indirect Measurements of Coherent Thermal Emission from a Truncated Photonic Crystal Structure

摘要

Recently, coherent thermal emission has been demonstrated using a multilayer structure consisting of a one-ndimensional photonic crystal coated on a silver layer, that is, a photonic-crystal-on-Ag structure. The key to enablingncoherent emission is to excite a surface wave at the photonic crystal-Ag interface in the stop band of the photonicncrystal. In this paper, we describe a detailed theoretical and experimental investigation of coherent thermal emissionnfrom the fabricated photonic-crystal-on-Ag structure in the near-infrared region. A Fourier-transform infrarednspectrometer, equipped with a specular reflectance accessory, was used to measure the spectral reflectance atnincidence angles of 10, 30, and 45 deg. In addition, a laser scatterometer was used to measure the angle-resolvednreflectance at the wavelength of 891 nm. The emissivity obtained from the measured reflectance exhibits temporalnand spatial coherence.The surface-wave dispersion relation at the photonic crystal-Ag interfacewas calculated usingnthe supercell method with modified matrix equations that guarantee the convergence of solutions, especially when anmetallic layer is involved. The resonance condition obtained from measurements closely matches the dispersionnrelation. Along with the dispersion curves, calculated field magnitude at the photonic crystal-Ag interface alsonconfirms the existence of surface waves where the field is highly localized.