Hybrid pumped gain-switched thulium fiber laser at a high repetition rate.

Abstract

A gain-switched all-fiber thulium laser at 2μm with high repetition rate has been demonstrated under a hybrid pumping scheme combined of a pulsed pump at 1.56μm and CW pump at 793nm. The in-band pulsed pump at 1.56μm triggers the gain-switching pulses while the CW pump at 793nm facilitates the energy storage. Therefore, the seed cavity delivers high energy pulses allowing the elimination of multistage amplification. Such hybrid pump configuration is effective for generating gain-switched pulses of high average power with better slope efficiency and pulse width of a few hundreds of a nanosecond. The optimized cavity under such hybrid pump configuration provides output power of 5.92W from the gain-switched oscillator with slope efficiency of 60% and pulse width of 300ns at a repetition rate of 344kHz. Maximum pulse energy of 17.2μJ and peak power of 53.9W has been achieved at this repetition rate. Stable gain-switched pulses at reduced pump pulse energy have been achieved by the use of a CW pump at 793nm. This novel pump configuration facilitates gain switch at higher repetition rates where enough pump pulse energy may not be available. The gain-switched laser also operates at 520kHz and 1.3MHz repetition rate by changing the 1.56μm pulsed pump and cavity length.