Effect of a Metal Plate on Total Reflection

The phase changes which occur on total reflection are modified when a metal plate is placed near and parallel to a totally reflecting boundary. In particular the phase difference between plane waves of equal amplitude, polarized in and perpendicular to the plane of incidence, can be varied from -π through zero and up to the value obtained without the plate. When the refractive index is greater than or equal to 1 + 2 1/2 , there are two positions of the plate for which the reflected wave is circularly polarized, and in which the electric vector rotates in opposite directions. Measurements of this effect have been made at a wavelength of 1.25 cm, with a microwave analogue of the optical spectrometer, and a 45° Perspex prism with faces 6 in. square. In view of the limitations due to diffraction the results are in good agreement with the theory, and are an elegant way of showing the presence of the evanescent wave beyond a totally reflecting boundary.