Widely and Continuously Tunable Nanosecond Pulsed Laser Source Around 3 μm

We present continuously tunable nanosecond pulses around 3 μm from a passively Q-switched dysprosium (Dy)-doped fluoride fiber laser using a Fe 2+ :ZnSe crystal saturable absorber (SA). In a F-P cavity, including a segment of 37 cm long Dy fiber and closed by two dichroic mirrors, stable Q-switching at the free- running wavelength of 2938 nm is gotten. Attributable to the short cavity and low SA initial transmission, the pulse width of 87 ns has been achieved, representing the shortest and also the first sub-100 ns demonstration of passively Q-switched fiber lasers in the mid- infrared (MIR), to our knowledge. Subsequently, a reflection-type diffraction grating, as the output coupler and wavelength selector, is introduced into the cavity instead, where the Dy fiber has been lengthened to 81 cm in order to obtain a wide tuning range. As a result, the Q-switched pulses can be continuously tuned across the range of 2750∼3320 nm (570 nm), with the varied pulse width of 120∼865 ns. This spectral range is also the widest of continuously tunable pulsed rare-earth-doped fiber lasers in the MIR. The results highlight the great potential of the combination of Dy-doped fluoride fiber and Fe 2+ :ZnSe crystal in wideband nanosecond pulse generation in the spectral region of 3 μm, hence providing a versatile tool for practical applications e.g., laser surgery, polymer processing, free-space communication, and infrared countermeasures.