Self pulsations and self Q-switching in Ho3+, Pr3+:ZBLAN fibre lasers at 2.87 μm

The temporal characteristics of the output of a single-clad Ho³⁺, Pr³⁺-co-doped ZBLAN fibre laser pumped by a Nd:YAG laser at 1064 nm has been found to exhibit a range of cw, self pulsation and self Q-switching output dynamics, dependent on the excitation and fibre conditions. An interpretation is considered based on stimulated Brillouin scattering and the effect of the excited state absorption (ESA). For long fibre (∼13 m) and for uni-directional pumping, the output was a continuous wave (cw), but for bi-directional pumping, a significant decrease in the stability of the output is observed and the output displayed well developed self pulsations. A train of self Q-switched pulses with mean pulse duration of 767 ns, a peak pulse power of about 2.8 W and an average power of 183 mW and with more than 80% pulse-to-pulse stability has been observed when pumped with 4.4 W into each end of the fibre. Self pulsation phenomena are also observed in unidirectional pumping for shorter fibre lengths of ∼9.2 m at high pump power and for 1.5 m fibre length at all pumps power. PACS 42.55.Wd; 42.60.Gd; 42.60.Mi