Vapor transport equilibration was used to prepare lithium niobate crystals of a variety of controlled off-congruent compositions. Crystals were characterized through measurement of the ferroelectric Curie temperature Tc and measurement of the temperature for noncritical phase matching TPM of second-harmonic generation from both 1.064- and 1.32-μm laser sources. Across the majority of the single-phase region, both Tc and TPM were observed to vary nearly linearly with Li/Nb ratio. The variation in TPM with Li/Nb ratio was observed to change direction within the single-phase region at some small but finite compositional interval away from the Li-rich phase boundary. Crystals equilibrated to the Li-rich phase boundary had excellent optical homogeneity. Preparation of Li-poor crystals was hampered by extremely slow lithium diffusivity and problems with second-phase precipitation.

Articles you may be interested inPredicting temperature dependence of the refractive index and nonlinear optical coefficients in lithium niobate An investigation was performed on the diffusivity of lithium in lithium niobate at 1100 "C in the crystallographic z direction over the composition range from 48.38 to 49.85 mol % L&O. A vapor transport technique was applied to produce a lithium niobate crystal with a widely varying diffusion-limited lithium concentration profile. The profile was measured through spatially resolved measurement of the phase-match temperature for frequency doubling of a Nd:YAG laser. A Boltzmann-Matano analysis was applied to the profile to estimate diffusivity as a function of composition. The validity of the Boltzmann-Matano results was examined through numerical simulation, taking into account finite interfacial mass transport. A dramatic increase of lithium diffusivity with Li/Nb ratio was observed, ranging from roughly 3 X 10d9 cm27s at the 48.38 mol % L&O congruent composition to roughly 50X lop9 cm2/s at 49.85 mol % Li,O.

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Photochromic ‘‘gray-track’’ damage occurring during 1064 nm second-harmonic generation (SHG) in KTiOPO4 is a significant limitation in many practical applications. Measurements of the evolution of gray-track damage during SHG, along with measurements of the 355 nm radiation simultaneously produced by non-phase-matched sum-frequency generation, are described. Comparison of these measurements with the gray-tracking induced by exposure to a single wavelength indicates that for the conditions investigated here, the gray-tracking during 1064 nm SHG is dependent only on the intensity of the 532 nm radiation. The dependence of the induced absorption on the 532 nm intensity is nonlinear, having a threshold of 80 MW/cm2, and an approximately linear increase for intensities above this threshold.