Rafał Ledzion

Application of polarimetric technique for determining the sign of quadratic electro-optic coefficients in crystals

So-called polarimetric methods are based on measurements of the intensity of light emerging from a modulator composed of a “sandwich” of investigated crystal placed between polarizer and analyzer. The polarimetric technique is known for its high accuracy in determining absolute values of electro-optic coefficients; however, the method is considered unable to find their signs. In this paper, we propose an examination of changes in the modulated signal phase that result from a controlled shift through the transmission characteristic of the modulator. We show that analysis of the changes allows one to obtain the sign of the coefficients. The sensitivity of the method is examined in measurements of quadratic electro-optic coefficients. It is found that the technique may be easily applied to crystals for which relatively low values of the coefficients, i.e., of the order of magnitude 10−20  m2/V2, are observed. Configurations where the light beam is sent along the optical axis and perpendicularly to the axis in a uniaxial crystal are considered. Examples of measurements of the quadratic electro-optic coefficients g1111−g1122 in KDP and ne3g3333−no3g1133 in DKDP are presented.