Indium selenide film: a promising saturable absorber in 3-to 4-μm band for mid-infrared pulsed laser

Indium selenide (InSe) film, an emerging two-dimensional chalcogenide semiconductor, has recently attracted growing interests in optoelectronics. However, its nonlinear characteristics and application potentials in mid-infrared (IR) region remain open, which is a very attractive but undeveloped spectral region currently. In this work, it is demonstrated that InSe film possesses excellent nonlinear absorption properties in 3- to 4-pm band. Saturable absorption measurements of InSe film at 2.8 and 3.5 mu m show very low saturation energy fluences and moderate modulation depths. Pump-probe measurements at 3 and 4 mu m indicate that InSe film has ultrafast responses in mid-IR region. Furthermore, the application of InSe film in mid-IR pulsed laser is demonstrated, and stable Q-switching operation of fiber laser at 2.8 mu m is realized. These results show that InSe film is a promising saturable absorber for mid-IR pulsed laser.