High performance 1.9 µm passively Q-switched bulk laser with germanene as a saturable absorber

Germanene is an analog of graphene, and its independent novel low-bending honeycomb structure gives outstanding advantages such as environmental stability and significant low-frequency optical absorbance. In this paper, the few-layer germanene was successfully prepared by the liquid phase exfoliation method. The saturable absorption characteristics of germanene in the infrared waveband were detected by the open-aperture Z-scan method. With germanene as a saturable absorber, a high-performance passively Q-switched bulk laser was realized at 1.9 µm. The shortest pulse width of 60.5 ns was obtained from continuous-wave pumping, corresponding to a single pulse energy of 6.7 µJ and peak power of 110 W. By utilizing the pulse pumping style with a repletion rate of 10 Hz, the single pulse energy and peak power increased to 45.8 µJ and 328 W, respectively, which exceeded all two-dimensional SA materials reported before. This research manifests that germanene is an excellent SA material for mid-infrared solid-state lasers.