Highly efficient 10 cm long fiber laser

We investigate an innovative multipass-pumping technique in a short photonic crystal fiber laser. The technique is based on simple optical elements and shows, in a power oscillator configuration, highly efficient CW and Qswitched operation of an extremely short fiber laser. We report significantly higher absorption of the pump light, compared to a single-pass configuration, which results in an impressive fourfold increase in slope efficiency, up to 60%. Moreover, we show pulse energy of 1.22 mJ and pulse duration shorter than 12 ns, corresponding to a peak power of more than 100 kW.