Abstract
Optical second-harmonic generation (SHG) is investigated in wedge-shaped PbHPO4 single crystals in various configurations of propagation and polarisation of the radiation between -50 and 75 degrees C. The temperature dependence of seven of the ten components of the nonlinear susceptibility is measured in the ferroelectric phase and absolute values are determined at -50 degrees C by comparison with quartz. In certain configurations of measurement the temperature dependence of the components follows closely that of the spontaneous polarisation PS(T). A small but finite SHG is observed in the paraelectric phase which can be attributed to short-range ferroelectric order.