Propagation of uniform plane waves in a Fabry-Perot resonator containing ammonium dihydrogen phosphate (ADP) as dielectric

The propagation of uniform plane electromagnetic waves in a uniaxial medium has been developed from an electrical rather than an optical viewpoint. Explicit formulae for the ratios of the magnitudes of electric field components along the three co-ordinate axes are worked out for ordinary and extraordinary wave normals, and the direction of energy propagation for both waves is also developed. The results are applied to a Fabry-Perot resonator with a dielectric of ADP and it is shown that the wave normal resonance angle is the same when the incident and reflected wave velocities inside the resonator differ by a maximum as when they are identical. This leads to circular interference fringes as with an isotropic medium which is a desirable feature in a Fabry-Perot intensity modulator.