Research and development of high-power, high-repetition rate, ultrashort pulse Yb-doped ceramic lasers

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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 … More 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