High energy Er-doped Q-switched fiber laser with WS2 saturable absorber

The report presents a stable Q-switched Er-doped fiber (EDF) laser with WS2-based saturable absorber (SA). The SA is obtained by mixing WS2 dispersion with polyvinyl alcohol (PVA) into polystyrene cells, and then evaporating them to form WS2/PVA film. The modulation depth (MD) of WS2/PVA is 2% and the saturable intensity (Isat) is 27.2  MW/cm2. Employing the WS2/PVA film into EDF laser cavity, stable Q-switched operation is achieved with central wavelength of 1560  nm. The repetition rate can be tuned from 16.15 to 60.88  kHz with increasing pump power from 30 to 320  mW. The single pulse energy increases from 82 to 195  nJ and then decreases down to 156 nJ with increasing pump power from 30 to 320  mW. The pulse width shows the same variation trend. The shortest pulse duration of 2.396  μs and the maximum single pulse energy of 195 nJ are obtained at the pump power of 220  mW. To the best of our knowledge, 195 nJ is the largest single pulse energy at 1.55  μm region with TMDs as Q-switcher. The signal-to-noise ratio (SNR) is measured to be 60  dB at the pump power of 130  mW. The long term stability of working is good too. The experimental results evidently show that the WS2/PVA SA can work as a promising Q-switcher for high power fiber lasers.