POLARIZED SPECTRAL EMITTANCE FROM PERIODIC MICROMACHINED SURFACES .3. UNDOPED SILICON - THE NORMAL DIRECTION IN SHALLOW LAMELLAR GRATINGS

Spectral polarized emittances from 400-degrees-C shallow lamellar gratings (depths up to 3-mu-m) normal to the surface with repeat distances of 10, 14, 18, and 22-mu-m 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-mu-m repeat distance, 3-mu-m deep and 6.5-mu-m 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.