Investigation into "hair" inclusions in large-sized KDP crystals grown by traditional method

Potassium dihydrogen phosphate (KDP) crystals are widely used in high-energy laser facilities for harmonic generation. An important defect observed in KDP crystals, known as "hair" inclusions in large-size crystals grown by traditional methods, was investigated using ultra-microscopy. Most of the "hair" inclusions within the crystals have a straight chain structure, while only a few displays a curved formation. The "hair" inclusions consist of multiple liquid inclusions and exhibit a chain- like structure with quasi-periodic features. The size of these liquid inclusions varies, ranging from 17.54 to 56.90 mu m, and show a chain density between 0.90 mm(-1) and 20.77 mm(-1) . The angles of the "hair" inclusion orientations about the c-axis range from 30 degrees to 79 degrees, corresponding to the dislocations in KDP crystals. Furthermore, the study examined the impact of "hair" inclusions on the transmittance of the crystals. This investigation aims to enhance the understanding of "hair" inclusions in traditionally grown KDP crystals and attempts to clarify the factors leading to the formation of these inclusions. It also offers a theoretical and experimental basis for reducing these inclusions in KDP crystals.