Radiation filters and emitters for the NIR based on periodically structured metal surfaces

The spectrally selective optical properties of wavelength selective radiation emitters and filters based on periodically microstructured metal surfaces were investigated. Metal surfaces were structured by the use of a holographic mask and subsequent etching processes. Due to the microstructure, thermally excited surface plasmons couple to electromagnetic radiation. Therefore a structured tungsten surface can act as a selective radiation emitter. The calculation of the absorptance by a rigorous diffraction theory allows the prediction of the emissivity of such structures. The angle dependent emissivity of tungsten gratings with periods of 1.4 mu m and 2.0 mu m was measured. A peak emissivity of 70% at a wavelength of 1.6 mu m was achieved. Band pass filters for the near infrared spectral range based on perforated metal films were investigated theoretically and experimentally. Filters with a grating period of 2.0 mu m were produced. A peak transmittance of 80% at a wavelength 2.9 mu m was achieved. The optical properties of the diffractive elements described partly show a strong angle dependence.