Optical properties of KNbO3

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Abstract
Measurements of birefringence and refractive indices in KNbO3 were performed in the orthorhombic, tetragonal and cubic phases. KNbO3 is phase matchable and collinear phase matching is possible for a Nd-laser. Absorption measurements reveal an exponential law for the absorption coefficient (Urbach tail). The dispersion of the refractive indices is discussed in terms of a single-oscillator model. The parameters obtained are in good agreement with those of other perovskite materials. Relations for the electrooptic effect in an orthorhombic oxygen-octahedron ferroelectric are derived and it is found that this effect can explain the observed temperature dependence of refractive indices. Finally, the coefficients for the linear electrooptic effect are calculated and discussed.