X-ray topographic studies of organic and non-linear optical materials

The flexible and non-destructive nature of X-ray topography is ideally suited to the study of large single crystals for both fundamental research and technological applications as well as the optimisation of crystal growth processes. Three examples are discussed, illustrating the application of X-ray topographic methods to non-linear optical (NLO) crystals. Synchrotron radiation section topography has been applied to the examination of large (up to 2 cm thick) organic crystals. Examples taken from the important NLO materials urea and 2-(α-methyl benzylamino)-5-nitropyridine (MBANP) demonstrate the advantages of this totally non-destructive assessment of crystal quality and illustrate the valuable insight into crystal growth history which can be obtained. X-ray topography has been used to examine growth defects and the quality of crystals of m-nitroaniline (mNA) grown by the Bridgeman method. These studies allow evaluation of growth parameters together with their influence on defect density and show that in the case of mNA, remarkably low defect densities can be achieved under optimum growth conditions. Double-crystal reflection topography, with synchrotron radiation has been used to image defects intersecting the {011} faces of the inorganic NLO material potassium titanyl phosphate (KTP). X-ray images have been combined with optical microscopy and interferometry to provide valuable information on the crystal growth process.