An improved half-shade system for the detection of elliptically polarized light

This paper describes the application of the reflection theory of Drude to the examination of surfaces. The essential characteristic of the method is that the state of polarization of the incident light is so adjusted that a plane-polarized beam is reflected. The absence of any ellipticity in this reflected beam is confirmed by means of an improved "ellipticity half-shade" system, with which two parts of a field of view can only be matched when the incident light is accurately plane-polarized. Two uses of this system are described. Details are given of the construction and use of the improved balanced ellipticity half-shade made from mica sheets, on the general principle of the Bravais biplate. The half-shade is shown to have a higher accuracy than a Babinet compensator.