Graphitic carbon nitride: A new saturable absorber for ∼3 μm

Graphitic carbon nitride (g-CN) based materials have been regarded as a novel class of multifunctional nanoplatforms for electronic, catalytic and energy applications. However, its optical characteristics have not received enough attention, yet. Although the theoretical bandgap of g-CN is quite large, which seriously limits the optical response range, various efficient strategies have been proposed to narrow the bandgap, such as heteroatom doping and defect control [1]. Surface sensitization, pore texture tailoring, heterojunction construction and co-catalyst loading have also been applied to promote the photoresponsivity of g-CN [1]. Furthermore, atomically thin g-CN nanosheets possess higher charge carrier density due to an obvious increase of density of states at the conduction band edge with respect to the bulk counterpart [2]. The saturable absorption response of g-CN has been demonstrated in the near infrared wavelength range [2, 3]. Here, we report on the fabrication of a g-CN saturable absorber (SA) and discuss its saturable absorption properties near 3 μm for the first time. By utilizing this home-made g-CN-SA, efficient Q-switched Er:Lu2O3 laser operation at 2.84 μm was realized, delivering a maximum average output power of 1.09 W and a pulse duration of 351 ns, which is among the shortest Q-switched pulses previously achieved with 2D-SAs in this wavelength range.