| Co-Investigator(Kenkyū-buntansha) |
MUSHA Mitsuru UEC, Institute for Laser Science, Assist. Prof. (40303028)
SHIRAKAWA Akira UEC, Institute for Laser Science, Assist. Prof. (00313429)
DONG Jun UEC, Institute for Laser Science, Researcher. (60401634)
KOUZNETSOV Dmitrii UEC, Institute for Laser Science, Researcher. (40401624)
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| Research Abstract |
We studied laser-diode-pumped femtosecond Yb-doped ceramic lasers for shorter pulse durations and higher powers. The success of Kerr-lens mode locking by use of sesquioxides (Re_2O_3, Re=Y, Lu, Sc) enables short-pulse mode-locking beyond general bandwidth limitations. For example, 92fs pulses with 850mW of output power from Yb:Sc_2O_3 was achieved. Ceramic lasers with multiple ceramics in a single resonator were also investigated. Broadening the gain bandwidth by use of Yb:Y_2O_3 and Yb:Sc_2O_3 simultaneously realized an output of 53fs and 1W, the record shortest pulse generation directly from an Yb solid-state oscillator. The series of our results show the powers and efficiencies are far beyond other materials in a sub-100fs region, and advanced the specifications of Yb solid-state lasers significantly. In addition, we have developed various composite ceramics and demonstrated a self-Q-switched microchip laser with 237ps of pulse duration, 172μJ of pulse energy, and 0.72MW of peak pow
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er by Yb:YAG/Cr:YAG.
For the development of temperature-tuned high-power active-mirror lasers, we investigated systematically the spectroscopic, thermal, and mechanical properties of YAG and Re_2O_3 ceramics. We developed a model including the temperature dependences of the stimulated emission cross section, population distribution within manifolds, temperature distribution in a gain medium and concentration quenching, and established how we optimally extract the energy from a temperature-tuned Yb:YAG laser. Higher-doping in a thinner medium is effective for power scaling of active-mirror lasers. We discovered, however, that when highly Yb-doped materials are pumped strongly, they are excited to a charge-transfer band by cooperative up-conversion and ultra-broadband emission is generated, giving the limitation. In highly Yb-doped Yb:YAG lasers, ceramics showed higher efficiency than single crystals, and as high as 60.6% Slope efficiency was obtained by 20% Yb:YAG. We can conclude that ceramics are suitable than single crystals for high doping since ceramics will have less impurity and hence the aforementioned nonlinear loss. Less
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