GB378742A - Improvements in rotatable compensators having a plano-parallel plate of doubly refracting material - Google Patents

Abstract

378,742. Doubly refracting elements. WINKEL GES., R., Gottingen, Germany. Dec. 10, 1931, No. 34223. Convention date, Dec. 13, 1930. [Class 97 (i).] A rotatable compensator for measuring the path difference of light rays in doubly refracting substances consists of a compound plane parallel plate made up of a number of plane parallel single plates cut from a doubly refracting crystal parallel to the optical axis and coordinated to each other in subtraction position, i.e. in such a position that, in the case of two plates, the path difference produced by the compound plate is the difference of the path differences produced by the two single plates. The compound plate e shown in Fig. 2 consists of two quartz plates l, k of equal thickness cut parallel to the optical axis and joined together so that the axes are at right-angles to each other in the two plates, i.e. in the plate l the axis corresponds to a line through the point m at right-angles to the drawing, while in the plate k the axis corresponds to the line n in the plane of the drawing. The plate is inserted in a rotatable mount c, Fig. 1, in such a position that the axis of rotation of the mount is parallel to the optical axis of the plate k. The mount c lies in an aperture b in a plate a which may for example be inserted between crossed Nicol prisms in a microscope. The compensator is rotated by a head h, the angle of rotation being measured on a scale i.