Ultra-low repetition rate mode-locked fiber laser with high-energy pulses.

This paper reports on the results of research into passively modelocked fiber laser with a record-setting optical length of the resonant cavity amounting to 3.8 km. Significant elongation of the laser resonator led to more than two orders of magnitude increase in the output pulse energy at the same pump radiation power. At ultra-low (for mode-locked lasers) pulse repetition rate (77 kHz) and pulse duration of 3 ns the energy per pulse reached 3.9 microJ. At this moment this is the highest pulse energy on record generated directly from a mode-locked laser without Q-switching, cavity dumping techniques, or additional optical amplifiers.