AT Crystals s.r.o. manufactures high-purity, large-dimension YAG (including doped variants like Yb:YAG, Nd:YAG) and sapphire crystals using proprietary horizontal directional crystallization technology. The crystals support high-power disc lasers, defense optics, aerospace components, medical lasers, and nuclear fusion systems. The company is headquartered in Žilina, Slovakia, collaborates with the University of Žilina, and was co-founded by Tomáš Gregor and Milan Gregor.