A new generation of oxide crystals is emerging for electro-optic Q -switching or control of highpower pulsed lasers. Unlike the acousto-optic Q -switches in which the total turn-off time is limited by the duration of sound wave propagation (110-220 ns/mm) across the beam diameter, the electro-optic devices provide a short (<10 ns) response needed for minimum losses. Extinction ratios of better than 100 : 1 for electro-optic crystals ensure their reliable hold-off. By contrast, acousto-optic devices are characterized by single-pass dynamic losses of approximately 40%, which hinders their use in high-gain lasers. The basic principles of electro-optic Pockels cells are discussed. The performance characteristics of Q -switching for traditional electrooptic materials [deuterated potassium dihydrogen phosphate (DKDP), lithium niobate (LNB)] and other new electro-optic crystals, such as barium metaborate (BBO) and crystals belonging to the langasite (LGS) and potassium titanyl phosphate (KTP) families, are reviewed comparatively. Particular emphasis is placed on KTPtype electro-optic crystals, primarily on rubidium titanyl phosphate RbTiOPO 4 (RTP), which stand out in their ability to provide Q -switching at extremely high frequencies or repetition rates up to 200 kHz. The use of both X -and Y -oriented double crystals as Q -switches in order to combine large electro-optic coefficients and low quarter-wave hold-off voltages with excellent thermal stability of the device is considered.

Ferroelectric domain structures of as-grown KTiOPO 4 crystals are observed on polished polar surfaces by the scanning secondary-electron microscopy ͑SEM͒ method. The results demonstrate a different contrast origin for domain boundaries and domains themselves. It is shown that the electron-beam irradiation in SEM causes a local heating of the ferroelectric crystal. Detailed calculations of the effects involved allow to assume that pyroelectric potentials induced by heating are opposite in sign for C ϩ and C Ϫ domains which is the main reason for the domain contrast. Domain boundaries are revealed due to the converse piezoelectric effect and the corresponding crystal deformations of ferroelectric domains are induced by electron-beam charging.

The origin of diversity in the reported ferroelectric phase transition (Curie) temperatures Tc, of KTiOPO4 (KTP) crystals grown from self-fluxes has been studied. A series of crystals has been grown by the top-seeded solution method from fluxes of different K/P molar ratios and solute concentrations, covering most of the KTP crystallization field in the K2O–P2O5–TiO2 ternary system. Curie temperatures of as-grown and high-temperature annealed crystals have been measured using the standard dielectric technique and found to spread from 883 to 960 °C. We show that the actual Tc values depend on the solution chemical composition, and a functional representation of this dependence is given. Inherent gradients of the Tc in as-grown KTP crystals are discussed in terms of the nonuniformity of their physical properties.

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