Abstract
We investigated various defects of the organic 4-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST) crystal to improve its laser-induced-damage tolerance for high-power terahertz (THz) application. We used DAST crystals grown by the slow-cooling method in methanol solution, and an irradiated infrared laser with a wavelength of 1550 nm without DAST absorption. It was found that laser damage was easily caused by crystal defects such as a rough surface, twin boundaries, and narrow-line defects (NLDs) in the bulk. In particular, NLDs are a serious problem that degrade the bulk laser-induced-damage tolerance of DAST crystals. The DAST crystals without such defects have high laser-induced-damage tolerance. To suppress the formation of crystal defects, we modified the crystal-growth conditions, and succeeded in growing DAST crystals with fewer defects than crystals obtained by the conventional growth process.