Cr2+: ZnSe crystal based high power passively Q-switched Tm-doped fiber laser

We demonstrate a high power passively Q-switched Tm-doped fiber laser with different initial transmission (IT) Cr2+:ZnSe crystals as the SA and varying gain fiber length. By employing 69% IT Cr2+:ZnSe crystal and 3.0 m length Tm-doped fiber, stable Q-switched pulse train having a repetition rate of 150.7 kHz and a pulse duration of 160 ns was obtained with maximum pulse energy of 8.74 µJ and highest level output power of 1.32 W at a slope efficiency of 20.1%. To increase the output power, 79% IT Cr2+:ZnSe crystal was used to decrease the intra-cavity loss. Stable Q-switched pulses with increased repetition rate and decreased pulse duration were achieved, but were finally terminated by unstable switching before reaching the maximum pump power which may be induced by partial two-photon absorption (TPA) and excited state absorption (ESA) of Cr2+:ZnSe crystal. Moreover, a longer Tm-doped fiber of 10.0 m and the 69% IT Cr2+:ZnSe crystal were also employed to improve the Q-switched pulses power by increasing the intra-cavity gain. Stable Q-switching until maximum pump power can be kept thus achieving the highest output power of 1.63 W which is, to the best of our knowledge, the reported most powerful Cr2+:ZnSe crystal based passively Q-switched Tm-doped fiber laser.