TEMPERATURE DEPENDENCE OF OPTICAL HARMONIC GENERATION IN KH2PO3 FERROELECTRICS.
HARVARD UNIV CAMBRIDGE MASS CRUFT LAB
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Optical second harmonic generation from KH2PO4 and KD2 PO4 platelets was measured as a function of temperature, above and below the ferroelectric transition point, between 77 K and 300 K. The nonlinear process is expressed by a third rank susceptibility tensor relating the second harmonic polarization to a quadratic function of the applied fields. A phenomenological theory is developed to account for the observed changes in the linear and nonlinear susceptibilities at the transition point. Relations between the tensor elements above and below the ferroelectric transition are obtained. The difficulties encountered in the experiment in the ferroelectric phase due to domains, and in the interpretation of the experimental data are discussed. The effects of atomic substitution on the relative values of the second harmonic susceptibilities was investigated by measurements at 300 K on the following isomorphs KH2PO4, KH2AsO4, KD2PO4 and NH4H2PO4. These substitutions have important effects on the low frequency dielectric and linear optical properties. Author