An experimental technique is described for determining the optical constants n and k of a metal by shining monochromatic light through thin films of the material and measuring the transmittance and phase change on transmission for samples of various thicknesses. The technique has the advantage, when compared to reflection techniques, that the results obtained are characteristic of the bulk material and are insensitive to surface conditions. Measurements were performed on vacuum-deposited gold films with thicknesses in the range from approximately 170 to 1800 Å, using lasers at wavelengths of 4880, 5145, and 6328 Å. In an attempt to evaluate the technique, the results obtained for the optical constants of gold are compared with those obtained by previous workers using different methods of measurement. In particular, the values obtained here are in agreement, within experimental error, with the recent work of Johnson and Christy.
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