Since our primary attempts to use Czochralski-grown YAP:Co,Si as Q-switching elements have failed, we also developed new technology of growth and thermal reduction of yttrium aluminium garnet (YAG) crystals doped with Co and Si. The crystals were found to be a promising material for optical applications, and especially useful as non-linear absorber (Q-switches) working in a broad spectral range of approx. 1150 to 1700 nm. Besides, it has a considerable absorption band around 600 nm which makes it useful in diode pumped lasers.

YAG:Co,Si single crystals were grown by the Czochralski method using Cyberstar Oxypuller. Thermal system consisted of iridium crucible of 50 mm diameter and a passive iridium afterheater of 60 mm diameter. Inductive heating with Hüttinger generator was used. It was very important that the cobalt ions were incorporated in specific locations in the crystalline lattice. To obtain this, we grew our crystals in nitrogen atmosphere with admixture of oxygen (1 vol. %), and the as-grown boules were next annealed in reducing atmospheres. As a result, good quality single crystals, [111]-oriented, with cobalt content of 0.4 at.% to 1.6 at.% and silicon content of 0.2 at.% to 0.6 at.% were obtained. They were up to 25 mm in diameter and up to 80 mm in length.