Abstract
Laser characteristics of diode-pumped Yb-doped materials have been improved at low temperature dramatically for high power operation. A laser system in the materials has been changed from quasi-three-level to four-level at low temperature. An emission cross section is enlarged and the reduced saturation fluence enables efficient energy extraction of the storage energy even by using commercially obtainable optics. In addition, thermal conductivity of laser crystals is considerably improved. In a diode-pumped laser oscillator with a cryogenically cooled Yb: YAG crystal, quantum-defect-limited operation has been demonstrated at 90 % optical slope efficiency. A Yb: YLF chirped-pulse regenerative amplifier has been developed at low temperature and 36-mJ, 800-fs pulses have been obtained at 20 Hz.
