Anisotropy of Molecular Optical Rotation. I. Transparent Media

Abstract

An examination is made of the experimental problem of measuring the optical rotation of an anisotropic fluid, with particular reference to the application of an electric field to an optically active medium. Exclusion of the rather large effects of induced linear birefringence (Kerr effect) and the provision of an adequate single‐to‐noise ratio are the most important considerations. Two cases are discussed: the ``parallel'' and the ``perpendicular,'' in which the direction of propagation of the light is respectively parallel and perpendicular to the applied electric field. The former permits a rigorous exclusion of the Kerr effect with inherent limitation of signal‐to‐noise ratios, and the latter, while providing signal‐to‐noise ratios of the order of 50 to 100 times greater, requires special care in the exclusion of the Kerr effect. The perpendicular case, which has heretofore received little attention, is analyzed in detail, and it is shown that in most instances satisfactory results cannot be obtained with a single pair of plane‐parallel electrodes. The use of two pairs of electrodes, having different azimuths, is suggested, and an analysis is given of the conditions under which exclusion of the Kerr effect may be obtained. Approximate calculations are made of signal‐to‐noise ratios which could be obtained in the perpendicular case with regard to both the Faraday effect and natural optical activity.