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, MoSeg, WSe2, etc.）. It has been proved that bulk ReS2 behaves as a stack of electronically and vibrationally decoupled monulayers, 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 midinfrared 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 μm are investigated systematically. Moreover, with cavity design, a femtosecond passively modelocked laser at 1.06μm 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.

Ta_(2)NiSe_(5) nanosheets as a novel broadband saturable absorber for solid-state pulse laser generation

Two-dimensional(2D)ternary chalcogenides have attracted great attentions because of their novel chemical and physical properties arising from the synergistic effect and stoichiometric variation with the additional third element compared with their binary counterparts.Here,high-quality 2D tantalum nickel selenide(Ta_(2)NiSe_(5))nanosheets are successfully fabricated by a liquid-phase exfoliation(LPE)method.The ultrafast excited carrier relaxation time and nonlinear optical absorption response are investigated and reveal that the prepared 2D Ta_(2)NiSe_(5)nanosheets have excellent broadband saturable absorption properties,which are further illustrated by three passively Q-switched(PQS)allsolid-state lasers operating at 1.0,2.0 and 2.8μm with the Ta_(2)NiSe_(5)nanosheet-based saturable absorber(SA).Furthermore,mode-locked laser operation with the pulse width as short as 356 fs is also realized at 1.0μm.This work not only demonstrates the excellent nonlinear optical proprieties and optical modulation performance of Ta_(2)NiSe_(5),but also paves the way for exploring the photonic and optoelectronic proprieties of ternary chalcogenide materials.