Study on improvement of the homogeneity of KDP crystals by annealing

Potassium dihydrogen phosphate (KDP) crystals were baked at varied temperatures in the same procedure. Three kinds of interference techniques were used to investigate stressinduced birefringence in KDP crystals. It was found that the annealing temperature greatly affects the improvement of the homogeneity of KDP crystal. Obvious improvement of homogeneity of KDP crystal was found after annealing at 50℃. With the rise of the annealing temperature, the extinction ratio increased. Growth ghost disappeared after annealing at 110℃. The extinction ratio decreased when the crystals were annealed at very high temperature, such as 170℃.