We have demonstrated a quantum-defect-limited operation in a diode-pumped Yb:YAG oscillator at low temperature. The highest slope efficiency of 90% at the crystal temperature of 70 K was obtained, which was close to the quantum efficiency of 91.2%. An optical-to-optical efficiency and a laser gain were 74% and 8 cm<sup>-1</sup>, respectively at a low pump intensity of 2.3 kW/cm<sup>2</sup>.

© 2004 Optical Society of America

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