Broadband rhenium disulfide optical modulator for solid-state lasers

Rhenium disulfide (ReS2), a member of group VII transition metal dichalcogenides (TMDs), has attracted increasing attention because of its unique distorted 1T structure and electronic and optical properties, which are much different from those of group VI TMDs (MoS2, WS2, MoSe2, WSe2, etc.). It has been proved that bulk ReS2 behaves as a stack of electronically and vibrationally decoupled monolayers, which offers remarkable possibilities to prepare a monolayer ReS2 facilely and offers a novel platform to study photonic properties of TMDs. However, due to the large and layer-independent bandgap, the nonlinear optical properties of ReS2 from the visible to mid-infrared spectral range have not yet been investigated. Here, the band structure of ReS2 with the introduction of defects is simulated by the ab initio method, and the results indicate that the bandgap can be reduced from 1.38 to 0.54 eV with the introduction of defects in a suitable range. In the experiment, using a bulk ReS2 with suitable defects as the raw material, a few-layered broadband ReS2 saturable absorber (SA) is prepared by the liquid phase exfoliation method. Using the as-prepared ReS2 SA, passively Q-switched solid-state lasers at wavelengths of 0.64, 1.064, and 1.991 mu m are investigated systematically. Moreover, with cavity design, a femtosecond passively mode-locked laser at 1.06 mu m is successfully realized based on the as-prepared ReS2 SA for the first time. The results present a promising alternative for a rare broadband optical modulator and indicate the potential of ReS2 in generating Q-switched and mode-locked pulsed lasers. It is further anticipated that this work may be helpful for the design of 2D optoelectronic devices with variable bandgaps. (c) 2018 Chinese Laser Press