Double beam photoelectric analysis of plane and elliptically polarized light

Abstract

A precision double beam balance method of analysing plane and elliptically polarized light is described which employs the technique of a large half-shadow angle. An optical system is used which consists of a double pair of Rochon prisms. This, together with suitable photoelectric cells, enables measurements to be made covering the spectral region 0.2-1.2 μm. The orientation of plane polarized light with reference to one of the calibrated analysing prisms is determined by using one beam as a reference signal and the other, containing the light to be analysed, as the measuring beam. Since both beams are derived from the same source the measurement is not affected by fluctuations of the light intensity. The sensitivity is in general limited by the divided circles which can be read to 1' of arc. The small rotations of the plane of polarization which occur in phenomena such as the Faraday and Kerr magneto-optic effects are measured by a monitored out-of-balance current method employing a 45° half-shadow angle technique. Here the sensitivity in general is considerably better than 1 of arc. Elliptically polarized light produced either by transmission of plane polarized light through an absorbing medium or by reflection from the surface of such a medium is analysed by first measuring the orientation of the major axis with reference to the analysing prism and then the axial ratio. The analysing prism is calibrated with reference to the plane of incidence of the reflecting surface. The two beams are used in turn as reference and measuring beams, each providing a large half-shadow angle for the other. It is sometimes necessary in the case of reflection to measure the principal angle with a high degree of precision. This is done by finding by interpolation the angle of incidence for which the elliptically polarized light has zero orientation. The principal angle is then measured in terms of the axial ratio at this angle of incidence.