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.

A compact saturable absorber mirror (SAM), based on multilayered black phosphorus (BP) nanoplatelets, was fabricated and successfully used as an efficient saturable absorber (SA) in a passively Qswitched Tm:YAP laser at 1.9 μm. With the BP SAM, Q-switched pulses with a duration of 181 ns and an average output power of 3.1 W were generated at a pulse repetition rate of 81 kHz. This resulted in a pulse energy of 39.5 μJ which, to the best of our knowledge, is the record among the reports on BP SA-based Q-switched lasers. In addition, the simultaneous dual-wavelength Q-switched operation at both 1969 and 1979 nm has been observed. The results indicate the promising potential of multilayered BP nanoplatelets as SAs for achieving efficient pulsed lasers at around 2 μm.

A novel two-dimensional (2D) material member in the transition metal dichalcogenides family, few-layered rhenium disulfide (ReS) was prepared by liquid phase method successfully. By using the open-aperture Z-scan method, the saturable absorption properties at 2.8 μm were characterized with a saturable fluence of 22.6  μJ/cm and a modulation depth of 9.7%. A passively Q-switched solid-state laser at 2.8 μm was demonstrated by using the as-prepared ReS saturable absorber successfully. Under an absorbed pump power of 920 mW, a maximum output power of 104 mW was obtained with a pulse width of 324 ns and a repetition rate of 126 kHz. To the best of our knowledge, this is the first demonstration of applying ReS in an all-solid-state laser. Moreover, this represents the shortest pulses in Q-switched MIR lasers based on a 2D material as the saturable absorber, which demonstrated the superiority of ReS acting as an optical modulator for generating short-pulsed lasers. The results well prove that 2D ReS is a reliable optical modulator for MIR solid-state lasers.

photonics and optoelectronics is the lack of materials with broad-band optical response and strong light-matter interaction. Therefore, it is an urgent need and many efforts have been devoted to searching for this kind of novel materials. [2][3][4][5] The broad-band optical response of 2D nanomaterial is related to the unique band structure and electronic properties. [1] Graphene exhibits a wide-spectral photonic response from ultraviolet to the radio-wave regimes owing to its gapless and conical-shape band structure. However, lack of intrinsic bandgap makes graphene-based devices suffer from relatively small on/off ratio, large dark current, and poor photo response. The relative low absorption and high non-saturable loss of graphene in optical response limit its extensive applications. [6][7][8][9] Following graphene, the most studied 2D transition metal dichalcogenides (TMDCs) possess a bandgap ranging from 1.0 to 2.0 eV, indicating their practical optoelectronic applications are not available in midinfrared (MIR) wavelength range. [10,11] After graphene and TMDCs, black phosphorus (BP), the most thermodynamically stable allotrope of phosphorus, has been thoroughly studied as a novel 2D layered material since early 2014. [12] It has triggered significant interests in both scientific research and potential electronic, optoelectronic, and biomedicine applications because of its unique and exotic properties. [13][14][15] Layered BP has a direct bandgap with layer-dependent variation over ≈0.3-2.0 eV, which gives rise to broad-band optical properties from visible to MIR region. The intrinsic layer-dependent direct bandgap gives rise to high on/off ratio and low dark current for electronic devices and makes BP an appropriate 2D material for MIR photonic applications. Moreover, the bandgap of BP can be efficiently tuned by electrical gating, which should pave the way for optoelectronic devices. [16] BP presents puckered structure with in-plane anisotropy, which results in specific dichroic optical properties of light absorption and photoluminescence. [17] However, easy oxidation under ambient environment is the biggest obstacle that significantly impedes its practical applications. [14,[18][19][20][21][22] Therefore, how to improve the long-term stability of BP has become a challenge.Germanium phosphide (GeP), a typical 2D group IV-V semiconductor, has attracted significant attention due to the advantages of higher thermodynamic stability than black phosphorus (BP), widely tunable bandgap, high carrier mobility, and in-plane anisotropy. However, its photonic and optoelectronic properties have not been extensively explored so far. Herein, large size and high-quality GeP single bulk crystal is successfully grown by flux method and stripped into 2D nanosheets with liquid phase exfoliation (LPE) and spin-coating methods. The broad-band photonic and optoelectronic properties of 2D GeP nanosheets are systematically investigated. First principles calculations are performed to verify its widely tunable bandgap from 0.43 eV f...

Atomically thin Bi2O2Se has emerged as a novel two-dimensional (2D) material with an ultrabroadband nonlinear optical response, high carrier mobility and excellent air stability, showing great potential for the realization of optical modulators. Here, we demonstrate a femtosecond solid-state laser at 1.0 µm with Bi2O2Se nanoplates as a saturable absorber (SA). Upon further defect regulation in 2D Bi2O2Se, the average power of the mode-locked laser is improved from 421 mW to 665 mW, while the pulse width is decreased from 587 fs to 266 fs. Moderate Ar+ plasma treatments are employed to precisely regulate the O and Se defect states in Bi2O2Se nanoplates. Nondegenerate pump-probe measurements show that defect engineering effectively accelerates the trapping rate and defect-assisted Auger recombination rate of photocarriers. The saturation intensity is improved from 3.6 ± 0.2 to 12.8 ± 0.6 MW cm−2 after the optimized defect regulation. The enhanced saturable absorption and ultrafast carrier lifetime endow the high-performance mode-locked laser with both large output power and short pulse duration.