Dramatic improvements in the laser characteristics of ytterbium-doped materials were experimentally shown by cooling an ytterbium-doped laser crystal at low temperature. Quantum-defect-limited operation has been demonstrated in a diode-pumped free-running oscillator with a cooled Yb:YAG. The highest slope efficiency of 90% was obtained at a crystal temperature below 70 K, which was close to the theoretical Stokes efficiency of 91.2%. The optical-to-optical efficiency and laser gain were 74% and 8 cm - 1 , respectively, at a low pump intensity of 1.3 kW/cm 2 . By using an Yb:YLF crystal at 77 K, a 60-mJ diode-pumped chirped-pulse regenerative amplifier has been demonstrated. After temporal compression by using a parallel grating pair, 36-mJ, 795-fs pulses were generated at a 20-Hz repetition rate.