Passively Q-switched 1.989 μm all-solid-state laser based on a WTe2 saturable absorber.

In this paper, the novel two-dimensional (2D) tungsten ditelluride (WTe2) was successfully fabricated by the liquid phase exfoliation method and used as a saturable absorber (SA) for a diode-end-pumped passive Q-switching Tm:YAP laser operating at the 2.0 μm wavelength band. The saturable fluence and the modulation depth of the prepared WTe2 SA were determined to be 5.1  μJ/cm2 and 7.2%, respectively. The maximum average output power of 0.64 W was obtained with the shortest pulse width of 368 ns at a pulse repetition rate of 78 kHz. The corresponding highest single pulse energy and largest pulse peak power were calculated to be 4.8 μJ and 12.7 W, respectively. To the best of our knowledge, this is the first time that WTe2 has been used as the SA for 2.0 μm solid-state bulk lasers. The results indicate that WTe2 should be an excellent SA for generating 2.0 μm pulsed lasers.