Photoelectric Analysis of Elliptically Polarized Light

Two photoelectric methods of analysis of elliptically polarized light have been devised. One is a development of that of Kent and Lawson in which a rotating analyser yields a zero signal only when the light is circularly polarized We use a double image prism after a rotating analyser and the two resulting modulated beams are in antiphase only when the axes of the double image prism coincide with the axes of the vibration ellipse. In our second method, the light is modulated by chopping, and a double image prism selects two components in phase In principle these are equal only when the axes of the double image prism are at 45° to the axes of the vibration ellipse Thus the directions of the major and minor axes are found, and if the outputs from the two photocells which receive the two components are balanced on an electrical bridge the axial ratio may be obtained. The double image prism plays here the part of the half shadow device in visual observations, but as its half shadow angle is 90° instead of only a few degrees, the photocells are used under optimum conditions, i.e the signal-to-noise ratio is maintained as large as possible and the potential accuracy of the method greatly exceeds the limitations imposed by the rest of the apparatus. By slight modifications the method may be made partially self-recording. Some examples are given of measurements made on metallic films undergoing surface changes.