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A formalism which allows finite ray tracing through monoaxial crystals was developed starting from Maxwell's equations. The derived formulas were applied to a Wollaston prism in convergent light and spot diagrams were obtained.

Direct measurements of the bulk photovoltaic current density in photorefractive and crystals were performed at high light intensities. Illumination of the crystals with light pulses of a Q-switched frequency-doubled Nd:YAG laser (pulse duration 20 ns; light wavelength 532 nm) yielded a photovoltaic current through the crystals which charged a capacitor. Afterwards an electrometer measured the voltage of the charged capacitor. From this voltage and from capacity and exposure time the current density was deduced. For intensities above a contribution to which increased quadratically with light intensity I appeared for crystals. Co-doping with Mg and Zn lowered the quadratic component. Our results are in good qualitative and quantitative agreement with previous holographic measurements and support the claim that the intrinsic defect acts as a secondary photorefractive centre in at high light intensities.