Q-switching, mode-locking and tunable operation around 0.9 ¿m of a neodymium-doped monomode fibre laser

Recent studies of monomode silica fibre which has rare-earth impurity ions incorporated into the core region have shown that it can exhibit laser action with low threshold and high efficiency when end pumped by an external laser source. In the paper we describe the first demonstration of Q-switching of the 4F3/2-4I9/2 Nd3+ transition at 0.9 ¿m using a fibre laser of this type. A birefringent filter has been used to tune the laser output over the range 0.900¿0.945 ¿m. We also report on the performance of the laser at 1.08 ¿m under conditions of Q-switching and active mode-locking. In Q-switched operation an intracavity acousto-optic modulator was used to generate pulses of 200 ns duration and 8.8 W peak power at repetition rates up to 1 kHz. Active mode-locking of the fibre was accomplished using acousto-optic modulation of the cavity losses at 41.4 MHz, converting the laser output to a train of pulses of subnanosecond duration.