No abstract

The relative optical absorption coefficient o, of polycrystalline slabs of cuprous oxide was measured at 295'K, 77'K, and 4.2'K. At 4.2'K, n is proportional to La is the wave number. At 77'K an additional component appears, so that n=ai+ces, with n&~Pa -E&g& and as~Po -E2]&. This is attributed to indirect transitions to exciton levels, in agreement with a theory by Elliott. The ratio of the integrated absorption coeKcient of the first two exciton lines, after corrections for the background were applied, is also in satisfactory agreement with the Elliott theory.

Spectroreflectometry was used to measure the refractive index of the following optical coating materials: Ta(2)O(5), HfO(2), Y(2)0(3), La(2)O(3), ZrO(2), CeO(2), CeF(3), LaF(3), NdF(3), MgF(2) in the 250-2000-nm spectral range.

Refinement and thin film synthesis methods were used by members of six different institutions to design antireflection coatings for germanium substrates. The solutions are based on the use of zinc sulfide and germanium layers only. Several systems were found with an average reflectance that is less than 1% in the 7.7 to 12.3 microm spectral region.

The phase shift upon transmission of a nonabsorbing multilayer is shown to be a monotonically decreasing function of the wave number, with an average slope proportional to the optical thickness of the coating. Two limiting situations of the phase shift upon reflection are examined: In one the phase monotonically increases with wavelength, and in the other the phase oscillates. The phase shift upon reflection is derivable from Kramers-Kronig-type relationships, provided the radiant reflectance and the Blaschke factors are known. Characteristic features of the refractive-index profile related to these factors are discussed.