ABSTRACT
Far-infrared laser calorimetry was used to measure the absorptivity, and thus the emissivity, of aluminum-coated silicon carbide mirror samples produced during the coating qualification run of the Herschel Space Observatory telescope to be launched by the European Space Agency in 2007. The samples were measured at 77 K to simulate the operating temperature of the telescope in its planned orbit about the second Lagrangian point, L2, of the Earth-Sun system. Together, the telescope's equilibrium temperature in space and the emissivity of the mirror surfaces will determine the far-infrared-submillimeter background and thus the sensitivity of two of the three astronomical instruments aboard the observatory if stray-light levels can be kept low relative to the mirror emission. Absorptivities of both clean and dust-contaminated samples were measured at 70, 118, 184, and 496 microm. Theoretical fits to the data predict absorptivities of 0.2-0.4% for the clean sample and 0.2-0.8% for the dusty sample, over the spectral range of the Herschel Space Observatory instruments.
ABSTRACT
The Micro-Stripes program has been used to calculate resonance wavelengths and the bandwidth of inductive cross-shaped metal meshes in contact with dielectric layers. The shift of the resonance wavelength, depending on the thickness of the dielectric layers, has been studied for two refractive indices. The transmittance of two mesh filters with dielectric spacers or embedded in a dielectric has been calculated for specific alignment of the crosses of one mesh with respect to the other. Transmission line theory has been used to calculate the transmittance of two mesh filters with nonaligned crosses and dielectric layers. A coupled oscillator model has been used for interpretation of the interaction of resonance and Fabry-Perot modes.
ABSTRACT
The transmittance of inductive single-layer and multilayer cross-shaped metal meshes has been calculated with the Micro-Stripes software program. The effect of symmetric and asymmetric alignment of the crosses of one mesh with respect to another was studied and compared with transmission line theory, which presents the nonaligned case. Significant differences are found for small spacing at approximately 1/5 the periodicity constant, whereas the differences disappear for large spacing. A pair of coupled surface waves is used to represent the mode of a single mesh. The resulting modes corresponding to the transmittance of multilayer metal meshes are interpreted by modes composed of resonance modes of a single mesh coupled by Fabry-Perot modes depending on the separation.
