Study of contributions to temperature dependence of the phase shift in an electro-optic crystal

The spontaneous and electric field induced phase retardations have been measured as a function of temperature in a KDP crystal using an accurate method. The plots of these retardations versus temperature reveal unexpected undulations. We consider the various contributions which could be involved in these dependences, such as the thermooptic effect, crystal dilatation and temperature dependence of the electro-optic coefficient. By means of calculations, the undulations are shown to be caused by an interference phenomenon related to light reflections on the surface of the crystal.