TRANSPARENCY IMPROVEMENT OF POTASSIUM TITANYL PHOSPHATE (KTP) CRYSTALS BY ANNEALING UNDER OXYGEN ATMOSPHERE

We have studied the influence of iron impurity, and the effects of annealing on KTiOPO4 single crystals. It was found that in high-power second harmonic generation, the iron concentration should be minimized. Annealing at 800-degrees-C caused the optical absorption edge to shift 5-10 nm towards shorter wavelengths, and for undoped crystals, the optical transmittance was also increased. Annealing in atmospheres of increasing oxygen concentration increased the transparency. A high recovery capability against X-ray irradiation damage was also obtained after annealing. The measured full width at half-maximum of the X-ray diffraction (800) peak was apparently decreased in annealed crystals.