Reflection, Absorption, and Emission of Light by Opaque Optical Gratings

Reflection, absorption, and emission properties of gratings in the visible region have been studied both theoretically and experimentally with special attention to Wood’s anomalies. The theory has been developed for both the electric vector perpendicular and parallel to the rulings. The optical properties of the grating material and the shape of the grating profile have been taken into account. Computations have been made on aluminum and tungsten gratings for the perpendicular electric vector. Reflectance of an aluminum grating has been measured with integrating-sphere techniques. The measurements are in qualitative agreement with the theoretical calculations. It is shown both theoretically and experimentally that Wood’s anomalies are associated with an increase of absorptance and emittance. This effect is especially pronounced when the grating material has low-loss plasma properties, as is the case with aluminum. The increase of absorptance and emittance of a periodic structure at Wood’s anomalies is not restricted to the visible wavelength range.