OPTICAL METHODS TO CHARACTERIZE THE COMPOSITION AND HOMOGENEITY OF LITHIUM-NIOBATE SINGLE-CRYSTALS

A number of the physical properties of lithium niobate strongly depend on sample composition. Although several procedures for the determinat ion of the composition have already been published, a critical survey and an introduction to standard methods recommendable also for laborat ories active in R&D of LiNbO3 devices is still missing. Within a detai led description of a series of methods, we summarise their capabilitie s and accuracy. The proposed optical characterisation methods, in part icular those based on the generation of second harmonic light and thos e involving the measurement of birefringence and the UV absorption edg e are found to be most convenient for an accurate and fast standard ch aracterisation of LiNbO3 single crystals. An absolute accuracy of 0.1 mol% based on a comparison with the Curie temperature calibration meth od and a relative accuracy of up to 0.01 mol% are available. Some of t hese methods are also suited for the two or three dimensional homogene ity control of LiNbO3 single crystals.