All solid‐state pulsed lasers (ASSPLs) play a significant role in the fields of medical, military, industry, and scientific research. Passive Q‐switching and mode‐locking are two of the most effective techniques for generating ASSPLs, in which a saturable absorber (SA) is the key element that has great impact on laser output parameters. Recently, 2D layered materials have been widely studied due to their intriguing properties. Their advantages of ultrafast dynamic processing, excellent nonlinear optical response, broadband operation, and easy fabrication and integration with lasers, enable them to be excellent SAs. Herein, the recent progress of ASSPLs with 2D layered material‐based SAs is reviewed, including a brief introduction of the fundamental characteristics, fabrication methods, characterization techniques of ultrafast dynamics, and nonlinear optical properties of 2D materials, design criteria of passively Q‐switched and mode‐locked bulk lasers, and their applications in ASSPLs. Finally, the potential developments and perspectives on 2D material‐based ASSPLs are also highlighted.
For van der Waals (vdW) heterostructures, optical and electrical properties (e.g., saturable absorption and carrier dynamics) are strongly modulated by interlayer coupling, which may be due to effective charge transfer and band structure recombination. General theoretical studies have shown that the complementary properties of graphene and MoS 2 enable the graphene/MoS 2 (G/MoS 2 ) heterostructure to be used as an important building block for various optoelectronic devices. Here, density functional theory was used to calculate the work function values of G/MoS 2 with different thicknesses of MoS 2 , and its relaxation dynamic mechanism was illustrated. The results reveal that the G/MoS 2 heterostructure interlayer coupling can be tuned by changing the thickness of MoS 2 , furthering the understanding of the fundamental charge-transfer mechanism in few-layer G/MoS 2 heterostructures. The tunable carrier dynamics and saturable absorption were investigated by pump−probe spectroscopy and open-aperture Z-scan technique, respectively. In the experiments, we compared the performances of Q-switched lasers based on G/MoS 2 heterostructures with different MoS 2 layers. Taking advantage of ultrafast recovery time and good saturable absorption properties, a femtosecond solid-state laser at 1.0 μm with G/MoS 2 heterostructure saturable absorber was successfully achieved. This study on interlayer coupling in G/MoS 2 may allow various vdW heterostructures with controllable stacking to be fabricated and shows the promising applications of vdW heterostructures for ultrafast photonic devices. KEYWORDS: G/MoS 2 heterostructure, nonlinear optical response, femtosecond solid-state bulk laser, saturable absorption, charge-transfer process
High-quality black phosphorus (BP) saturable absorber mirror (SAM) was successfully fabricated with few-layered BP (phosphorene). By employing the prepared phosphorene SAM, we have demonstrated ultrafast pulse generation from a BP mode-locked bulk laser for the first time to our best knowledge. Pulses as short as 6.1 ps with an average power of 460 mW were obtained at the central wavelength of 1064.1 nm. Considering the direct and flexible band gap for different layers of phosphorene, this work may provide a possible method for fabricating BP SAM to achieve ultrafast solid-state lasers in IR and mid-IR wavelength region.
Rhenium disulfide (ReS 2 ), 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 (MoS 2 , WS 2 , MoSe 2 , WSe 2 , etc.). It has been proved that bulk ReS 2 behaves as a stack of electronically and vibrationally decoupled monolayers, which offers remarkable possibilities to prepare a monolayer ReS 2 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 ReS 2 from the visible to midinfrared spectral range have not yet been investigated. Here, the band structure of ReS 2 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 ReS 2 with suitable defects as the raw material, a few-layered broadband ReS 2 saturable absorber (SA) is prepared by the liquid phase exfoliation method. Using the as-prepared ReS 2 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 1.06 μm is successfully realized based on the as-prepared ReS 2 SA for the first time. The results present a promising alternative for a rare broadband optical modulator and indicate the potential of ReS 2 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.
Few-layered titanium carbide (TiCT), a novel two-dimensional (2D) Van der Waals material in the MXene family, was fabricated with a liquid-phase method and applied as a saturable absorber for a continuous-wave mode-locked femtosecond bulk laser. Pulses as short as 316 fs with a repetition rate of 64.06 MHz and maximum output power of 0.77 W were achieved at the central wavelength of 1053.2 nm, demonstrating the first known, to the best of our knowledge, application of MXene in an all-solid-state laser. Considering the flexible band gap for different surface functional groups of TiCT, these results may promote the development of ultrafast photonics and further applications of 2D optoelectronic layered materials in the infrared and mid-infrared regions.
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