Losses in BeO ceramic waveguides in the 10.6 μ region

Infrared reflection and Raman scattering spectra of a single crystal of BeO and of BeO ceramic were studied. It was then possible to establish the form of the permittivity function whose values determine the infrared Q factor of waveguides made from these materials. The ceramic was found to be a polycrystalline material whose damping constant for optical phonons exceeded the corresponding value for a single crystal by roughly 30%. Consequently, in the 10.6 μ region, the losses in an "ideal" ceramic waveguide (i.e., neglecting the irregularities of its internal surface) exceeded those in a waveguide made from a single crystal by a factor of roughly 1.5. A comparison of the infrared reflection spectra of the ceramic and of a single crystal indicated that when calculating the losses in real ceramic waveguides one must take these irregularities into account and so also the scattering processes associated with them and, possibly, the excitation of surface polaritons. The structure of the reflection spectra was found to be a function of the sintering regime of the ceramic.