Passively continuous-wave mode-locked Er^3+-doped ZBLAN fiber laser at 28 μm

An Er(3+)-doped ZrF(4)-BaF(2)-LaF(3)-AlF(3)-NaF (ZBLAN) fiber laser was passively mode-locked by inserting a Fe(2+):ZnSe crystal into the free space part of the cavity. Continuous-wave mode-locked pulses at 2.8 μm with a pulse duration of 19 ps estimated from the spectral bandwidth and an average power of 51 mW were generated when a collimated beam traversed the Fe(2+):ZnSe crystal, while Q-switched mode-locked pulses were obtained when the Fe(2+):ZnSe crystal was illuminated by the focused beam.