Visible Q-switched pulse laser oscillation in Pr-doped double-clad structured waterproof fluoride glass fiber with graphene

We successfully generated a visible Q-switched pulse train at 636 nm in a Pr-doped double-clad structured waterproof fluoride glass fiber with graphene as a saturable absorber (SA) and calculated the slope efficiency as 22.1%. The average radio frequency and the average pulse width of all observed pulses were respectively measured as 633 kHz and 185 ns. We also discussed the required intensity to generate Q-switched operation in graphene using extrapolation and estimated the required intensity of Q-switched oscillation with graphene from kW/cm2 to MW/cm2 depending on wavelength.