Abstract
In development of tungsten microcavity illuminants and tungsten cluster illuminants, the Complex Reractive Index of tungsten at the operating temperature of 2000-6000 K is necessary to evaluate their luminous efficacy and lifetime. Little is, however, known about the complex index of tungsten in such a high temperature region.
In this study, we have determined the complex index of tungsten using an ellipsometer at room temperature. In measurement, a He-Ne laser of 633 nm and a Nd: YAG laser of 532 nm were used as the light sources. The measured complex index of tungsten was 2.0 to 3.0 in real part and 2.5 to 3.0 in imaginary part at 633 nm. Also, the corresponding components at 532 nm were 1.8 to 2.8 and 2.4 to 2.8. Repeatable accuracy was estimated about 1 % in measuring the complex index repeatedly at the same point on individual tungsten plates. It was, however, found that the measured complex index was linearly proportional to the reflectivity. This dependence is attributed to surface conditions such as oxidation and roughness on a microscopic scale.
