By combining reflectance spectroscopy and spectroscopic ellipsometry, the complex dielectric function of SrTiO, in the frequency range 40-5000 cm-' at 20, 100, 200, and 300 K has been determined. Using a factorized description, analytical expressions for the optical quantities were derived, giving excellent agreement with the experimental data. These can be used for two-layer fits of films on SrTiOs, e.g., of high-T, superconductors. The fit parameters complement very well those found at higher temperatures. 0 1995 American Institute of Physics.

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A far-infrared rotating-analyzer ellipsometer which uses a step-tunable, optically pumped gas laser as its light source is described herein. As polarizers novel metal grids with 10 000:1 polarization contrast were used. The instrument determines the complex dielectric function in the spectral range between 10 and 150 cm−1. A cryostat allows both reflection and transmission measurements from 10 to 330 K. Measurements of the birefringence of crystalline quartz, of both the carrier density and the scattering frequency of doped semiconductors, and of the low energy excitations of high-TC YBaCuO ceramics are presented herein.

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