Determination of Absolute Signs of Microwave Nonlinear Susceptibilities

The sign of the microwave nonlinear susceptibility has been found for the first time for a number of acentric crystals. The method used determines the absolute sign without recourse to a comparison crystal. Using known signs of piezoelectric coefficients to specify crystal orientation, all of the nonlinear susceptibilities measured are negative. Predictions of signs and magnitudes of some coefficients in pyroelectric crystals are also made.