Polarized spectral emittance from periodic micromachined surfaces: V Undoped silicon: angular measurement in shallow lamellar gratings

Experimental results of thermal emittance from lamellar gratings in intrinsic silicon are presented along with a theoretical discussion. For azimuthal angular directions in shallow gratings, enhanced thermal emission plateaus and maxima are observed. In the case of p-polarized emission in the Phi = 90 degrees azimuth (parallel to the grating vector), the plateau arises when two diffractive orders can be supported; it lies between the Rayleigh polar angles corresponding to the forbidden zone. The experimentally observed angular dependence of the s-polarized emission for the Phi = 90 degrees azimuth has been compared with a coupled-wave calculation, and a respectable agreement has been obtained. For the experimentally observed s-polarized emission in the Phi = 0 degrees azimuth (perpendicular to the grating vector), there is an onset of enhanced emission at the polar angles that follows a simple empirical relation unrelated to any known diffraction law. By contrast, the p-polarized emission in the Phi = 0 degrees azimuth shows relatively little structure. These data illustrate the value of thermal emission for surveying multivariate absorption processes involving microstructures.