Low Temperature Hydrothermal Growth Of KTi0PO4(KTP)

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Abstract
KTP possesses superior properties in its use as a nonlinear optic material with Type II phase matching. It is not hygroscopic, has a large effective nonlinear coefficient, excellent optical damage resistance, small beam walk-off angle, and large thermal and angular bandwidths. These combined factors have dictated its choice as a second harmonic generator when compared to previous materials. Ba2NaNb5015 was difficult to grow, KH2PO4 is hygroscopic, LiO3 has small spectral bandwidth, and LiNbO3 suffers optical damage easily. Even the recent 13-BaB204 has a larger walk-off angle, smaller angular acceptance, and a smaller d coefficient. In addition, the larger acceptance angle for KTP results in higher output for miniature configurations at low power input. KTP has now found new applications for optical waveguiding, sum frequency mixing, and parametric oscillators. The applications requiring large size have been limited because of the difficulty of growing single crystals. The use of high temperature and pressure aqueous solvents (hydrothermal crystallization) or the use of high temperature molten salt solvents limits the size of useful crystals. Hydrothermal crystal growth at a lower temperature offers potential advantages for size, cost and quality. Recent laboratory experiments suggested that growth may be performed near 400° C. In this paper, we report the scale up of this method to results in commercial sized activities. Our preliminary data indicate that favorable growth can be maintained at temperatures of 100° C lower than previously. We have examined selected physical properties of our low temperature crystals and compared them to those from normal growth. All of our measurements indicate a KTP crystal fully comparable to previous samples. Our process represents a major advance in scale up of growth technology for this important material.

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