A New Method of Diagnostics of the Quality of Heavily Yb-Doped Laser Media

A new method of optical material diagnostics by measuring the heat release under illumination is proposed. Narrowband radiation triggers certain mechanisms of heating, while direct temperature measurement allows obtaining the amount of heat release in the medium. The mechanisms of heat production in heavily doped Yb:YAG crystals grown by different techniques are investigated using the new method. Thin-disk active elements made of such crystals are examined for lasing efficiency and heat sources under laser operation conditions. The experimental data on disk laser heating differ from the calculated ones. A non-radiative excitation decay is found to be a significant heat source in highly doped Yb:YAG active elements under intense pumping. It is caused by the upconversion process and impurities. The thin-disk active elements of higher purity crystals have greater lasing power and efficiency. The new method of diagnostics shows its efficiency and conformity with the lasing experiment and the data obtained from other sources.