RESUMO
A method for the measurement of the thermal emissivity of films on substrates and for the subsequent determination of the optical constants is described. It is applied to sputtered amorphous silicon films on sapphire substrates. The results, obtained in the 3-6.3-microm spectral range and at 400-800 degrees C, confirm the existence of residual ir absorption in this region with an absorption coefficient on the order of 10(2).
RESUMO
The coupling of scattered radiation from Raman-active core and cladding regions to the waveguide normal modes is analyzed by treating the scattered light as a classical incoherent effective source. Numerical results are presented for the limiting cases of single-mode or highly multimode excitation of the fiber. The effect of a finite frequency shift between the exciting and scattered fields is also considered. It is found that radiation produced by scattering of the evanescent field in the cladding is coupled to the guided modes with a peak efficiency of about one-fifth that of light scattered in the core. The implications of these effects for optical devices utilizing fibers are briefly discussed.