Electrochemical Peeling Few-Layer SnSe for High-Performance Ultrafast Photonics.

In recent years, the photoelectric properties and nonlinear optical properties of layered metal chalcogenides (LMCs) have attracted extensive attentions. Because of lower phonon thermal conductivity, larger energy storage rate, and larger electron mobility, LMCs are widely studied in the fields of thermoelectric energy conversion, battery electrode materials, and semiconductor devices. As 2D LMCs, SnSe nanosheets (Ns) are connected to each other by van der Waals force, which makes it possible to use electrochemical methods to help peel off the thin layer structure. Two-dimensional SnSe has obvious adjustable band gap characteristics. Its thickness can be controlled to keep it on the desired band gap. In this article, we prepared a thin layer of SnSe by electrochemical methods and detected its nonlinear optical characteristics. It shows that our prepared materials have good optical absorption characteristics; it has a modulation depth of 15% and a saturation intensity of 61 MW/cm. To investigate the nonlinear effects of SnSe in short and long cavities, the Q-mode-locking phenomenon was first achieved in a fiber laser with cavity length of 6 m. After increasing the cavity length to 56 m, the pump power is adjusted to achieve an adjustable repetition frequency from MHz to GHz in turn in an Er-doped fiber laser through utilizing an SnSe incorporating a tapered fiber as a saturable absorber (SA). The nonlinear optical properties of thin layer SnSe are fully proven, which opens a new way for advanced photonics, optical communication, laser measurement, and other fields.