1590-nm-pumped passively Q-switched thulium all-fiber laser at 1900 nm

We propose and demonstrate a passively Q-switched 1900-nm thulium all-fiber laser using the mode-field-area mismatch method. A thulium fiber laser was core-pumped at 1590 nm and saturable-absorber Q-switched at 1900 nm through the use of a thulium saturable absorber fiber that had a relatively smaller mode field area than the gain medium. Sequential pulsing with a pulse energy of 12 μJ and a pulse duration of 160 ns was obtained. The pulse repetition rate was increased linearly with the applied pump power. With a pump power of 4.5 W, an average output power of 0.61 W and a pulse repetition rate of 50.7 kHz were achieved.