Birefringence of muscovite mica

Birsfringence of muscovite mica (n(e)-n(o)) is usually calculated from the dispersion relations of the indices n(e) and n(o). As small differences bet ween relatively large experimentally-measured values, the few available dat a for birefringence of mica ore widely distinct and sometimes contradict ba sic experimental facts. A different procedure is adopted in this work; to m easure birefringence directly as a single quantity in terms of the thicknes ses of mica plates and the wavelengths at which they act as quarterwave or halfwave phase retarders. Birefringence is found to decrease gradually from -0.0040 at 420 nm to -0.0046 at 700 nm in conformity with pertinent indepe ndent experimental results. (C) 1999 Elsevier Science Ltd. All rights reser ved.