High resolution infrared measurements of the OH− bands in KTiOPO4

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Abstract
High resolution infrared transmission measurements were performed at 10–300 K on KTiOPO4 crystals grown by hydrothermal or flux methods. The previously reported low resolution OH− band at 2.8 μm resolved into more than 100 lines. The strongest line was identified as a pure OH− stretch which broadened as T2, whereas lines which broadened as T1 were attributed to combinations with librations or other vibrational transitions. Although the integrated OH− related absorption strengths for several crystals were equivalent (±10%), the relative absorption strengths for various groups of lines scaled together and correlated with frequency doubling efficiencies; this indicated the possible occupation of several nonequivalent OH− sites in the lattice. Thus, only a portion of the OH− impurity was detrimental to the nonlinear polarizability.