With a dichroic mirror and a variable transmittance mirror as a resonant cavity

this paper realizes the continuous and Q-switching of a double-clad Tm3+-doped fiber laser pumped by a 792 nm laser diode.The experimental results show that the optimal output transmittance of the gain fiber exists when the pump power and fiber length are fixed and the laser power output is the largest.With 70% of the optimum transmittance

the obtained laser center wavelength is 1 930 nm

its output power is5.9 Wand the corresponding slope efficiency is 46%.Then it conducts the stable passive Q-switching of the fiber laser by using graphene dispersion liquid as a saturable absorber and inserting it between the gain fiber and the output mirror.When the pump power rises to 3.4 W

it obtains the maximum average output power of 39 mW with the corresponding pulse width of0.9μs

pulse repetition rate of 67 kHz and single pulse energy of 210 nJ.In addition

the average output power and pulse width are approximately linear with the incident pump power.