Polarized spectral emittance from periodic micromachined surfaces—III. Undoped silicon: The normal direction in shallow lamellar gratings

Spectral polarized emittances from 400°C shallow lamellar gratings (depths up to 3 μm) normal to the surface with repeat distances of 10, 14, 18, and 22 μm are presented. Both P and S emittance maxima are observed. The position of the P maxima are in general agreement with predictions of the Rayleigh model for the disappearance of diffracted orders. Comparison of the measured normal, spectral S polarized emittance of an intrinsic lamellar silicon grating with 10 μm repeat distance, 3 μm deep and 6.5 μm. wide slots, showed quite good agreement to a coupled wave calculation for a comparable structure. The agreement suggests that there is significant spatial coherence in the thermal radiation emitted from these grating structures.