Optical Constants of Sodium and Potassium from 0.5 to 4.0 eV

Ellipsometric experiments have been performed on thick evaporated films of Na and K both by single reflection at free surfaces and by multiple reflection at metal-fused silica interfaces. The results are in qualitative agreement with the nearly-free-electron model, exhibiting no anomalous peaks and showing interband transitions with thresholds at the expected frequencies. The values deduced for the optical masses are $1.14m$ for Na and $1.17m$ for K.