Michihiro Nakai

Population inversion factor dependence of photodarkening of Yb-doped fibers and its suppression by highly aluminum doping

We have confirmed that the photodarkening of Yb-doped fiber (YbDF) has the second-power dependence on a population inversion factor. The photodarkening of a newly developed highly aluminum-doped YbDF has been significantly suppressed

30W Q-SW fiber laser

We present an adaptive and robust pulse-operated high power fiber laser, which has an average output power of 30 W. The fiber laser realizes flexible pulse duration without changing a repetition rate and an average power, which is desirable for laser processing, by employing a Q-switched (Q-SW) Master Oscillator Power Amplifier(MOPA). For instance, its pulse duration is controllable in the range of 50 ns to 100 ns at 50 kHz in repetition rate. In addition to the flexible pulse duration, the fiber laser provides high powers, a peak power of 27 kW at 30 kHz in repetition rate and an average power of 30 W at 50 kHz in repetition rate. Large mode area (LMA) fibers and end pumping structure in the laser also contribute the above mentioned features, pulse adaptiveness and high output power. In terms of the robustness of the laser, we employ newly-developed reflection-suppressing pump combiners, which protect pump laser diodes (LDs) from amplified reflected signal light from objectives. All those features make the fiber laser a more practical light source for laser processing.