Evaluation of High Power Q-switched Tm~(3+) -Doped Silica Fibre Lasers Operating Near 2 μm

摘要

The operation and performance characteristics of three different modulation techniques for the Q-switching of Tm~(3+) doped silica fibre lasers operating near 2 μm are described. Various Q-switched regimes are observed for a range of modulation frequencies and fibre lengths when the fibre is end-pumped with a high power Nd: YAG laser operating at 1.319 μm in a linear bidirectional cavity. A larger multimode fibre core of 17 μm diameter is used to increase the laser gain volume and achieve higher pulse energy. Experimentally this laser produced pulses with a peak power of 18.5 W, at higher repetition rate of approximately 20 kHz, a single Q-switched pulse of duration 300 ns at full width at half-maximum (FWHM), and 5.5 μJ are observed using an optical (mechanical) chopper. A peak power of ～ 3.3 kW and pulse duration of 320 ns (FWHM) at low repetition rate of 50-70 Hz and highest pulse energy up to 2.3 mJ by using an electro-optic modulator (EOM) is obtained. This peak power is enhanced to be 4.1 kW and the shortest pulse duration at FWHM of 150 ns at low repetition rates of 100-500 Hz when using an acousto-optic modulator (AOM). The results presented show that Q-switching is currently limited by the performance of the intracavity modulator. In this paper, an evaluation is presented of the high performance of active Q-switched Tm~(3+) doped fibre lasers using various techniques, some reasons for the difference in performance are discussed and some potential routes to further improvements are described.