Precise Measurements of the Quadratic Electro-Optic Effect in KH₂PO₄ Crystals Using a Sénarmont-Type System

This paper presents precise measurements of the temperature dependencies of the quadratic electro-optic coefficients g1111-g1122 and ne3g3333-no3g1133 in KH₂PO₄ crystals. In addition to traditional electro-optic coefficients describing changes in the function of an applied electric field, intrinsic coefficients, defined in terms of induced polarization, are also considered. Both intrinsic coefficients decrease with increases in temperature, but the relative temperature changes are of different orders of magnitude: 10^-4 and 10^-3 K^-1. A Sénarmont-type setup was used for the electro-optic measurements. To achieve the best accuracy, a new approach was developed, in which, instead of using only one specific point on the modulator's transmission characteristic, the operating point is changed during the measurements.