G.Malovichko, V.Grachev

Summarising the publisheddataand the results obtained by usforpotassium titanyl phosphate KTiOPO4(KTP)we can conclude the following.

1.At present there are no ready recipes how to avoid the grey tracking effect. Different defect centres have been studied in the literature. The most of them are the products of photochromic damage, however, the real origin of this effect is still not clear.

2.Due to complexity of the intrinsic and extrinsic defect subsystems of KTP crystals and due to their interrelations, there are practically no chances to understand the origin of the grey tracking and to manage with it without an intense and detailed study of both defect subsystems.The radiospectroscopic methods (Electron Paramagnetic Resonance,EPR,Electron Nuclear Double Resonance,ENDOR, andsimultaneous EPR-optical spectroscopy) are indispensable for theclarification ofthe reasons of optical damage phenomenaand for the determination ofa possible way to prevent grey tracking.

3.Formulated tasks can not be solved without close co-operationofcrystal growersand researchers.In the laboratory ofmagnetic resonacespectroscopy at Osnabrück University the most necessary prerequisites for the solution of the tasks are already present.

On the basis of our knowledge and research experience, we can consider the discussed problems as rather complicated applied tasks. However, they do not look like hopeless problems, because some of the ways are already seen to be tried, at least, to increase the resistance of KTP crystals to the photochromic damage.