Blue light generation using bulk single crystals of niobium-doped KTiOPO4

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Abstract
We report here new solid‐solution KTiOPO4 (KTP) isomorphs, namely K1−xNbxTi1−xOPO4 and K1−xTaxTi1−xOPO4, suitable for the second‐harmonic generation (SHG) of blue light. Aliovalent substitution of the Ti4+‐K+ pair in KTP with Nb5+ or Ta5+ increases substantially the optical birefringence (nz−ny,x) of KTP, and blueshifts the SHG cutoff wavelengths for propagation along the x and y axes. A birefringence increase of ∼70%, and a SHG cutoff wavelength as short as 892 nm have been experimentally observed in crystals of K1−xNbxTi1−xOPO4. Detailed single‐crystal x‐ray structure determination reveals that the Nb substitution is ordered, with Nb strongly favoring the cis‐Ti(1) sites. We discuss possible correlation between this preferential substitution and the observed compositional dependence of nonlinear susceptibilities d24, and d15. Optimal solid‐solution compositions for the noncritically phase‐matched frequency doubling of the 1.064 and 0.946 μm lines of Nd:YAG lasers are presented, and potential applications for these new materials are outlined.

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