The Optical Constants of Solid Caesium

The caesium mirror was prepared by filling a glass cell having two optical glass windows with liquid caesium distilled over in vacuum, the metal then being allowed to solidify. The index of refraction and the coefficient of absorption were determined by the polarimetric method. The caesium on glass mirror was placed in optical contact with the hypothenuse side of a right angle prism so that the light entered one leg and came out of the other. The absolute index of refraction was obtained from the observed value by multiplying the latter by the index of refraction of the glass, the coefficient of absorption remaining the same. The index of refraction was found to vary from 0.362 for $\lambda 4550$A to 0.350 for $\lambda 6800$A with a minimum value of 0.321 for $\lambda 5890$A The coefficient of absorption increased from 2.37 for $\lambda 4550$A to 4.34 for $\lambda 6800$A The principal angles of incidence and of azimuth calculated by means of Drude's formulas increased from 55°25′ and 38°32′ respectively for $\lambda 4550$A to 63°20′ and 40°6′ for $\lambda 6800$A The corresponding values of the reflecting power were 44.2 and 66.1 per cent. The computed reflecting power of caesium in contact with crown glass increased from 48.5 per cent for $\lambda 4550$A to 63.2 per cent for $\lambda 6800$A. A direct spectro-photometric determination yielded corresponding values of 37.2 and 63.2 per cent, the agreement being best in the yellow and red end of the spectrum.