Observation of photoexcited emission clusters in the bulk of KDP and laser conditioning under 355-nm irradiation

Defect clusters in the bulk of large KDP crystals are revealed using a microscopic fluorescence imaging system and CW laser illumination. Exposure of the crystal to high power 355-nm, 3-ns laser irradiation leads to a significant reduction of the number of observed optically active centers. The initially observed defect cluster concentration is approximately 10(4)-10(6) per mm(3) depending on the crystal growth method and sector of the crystal. The number of defect clusters can be reduced by a mm factor of 10(2) or more under exposure to 355-nm laser irradiation while their average intensities also decreases. Spectroscopic measurements provide information on the electronic structure of the defects.