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Given the substantial π-electron delocalization observed in 4

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This study explores the wavelength-dependent and pulse-width-dependent nonlinear optical properties of liquid-phase exfoliated molybdenum sulfide selenide (MoSSe) nanosheets. The saturable absorption response of MoSSe nanosheets in the visible region is better than that in the near-infrared region, and the response under 6-ns pulse excitation is better than that of a 380-fs pulse. Furthermore, based on the first-principles calculations, we designed a phase modulator and optimized its structure by integrating a monolayer MoSSe into a silicon slot waveguide. The simulation results revealed that the phase shift could achieve a high optical extinction. Consequently, MoSSe exhibits satisfactory nonlinear optical properties and an excellent potential for applications in optoelectronic devices.

This work systematically investigates the third-order nonlinear optical (NLO) properties and ultrafast carrier dynamics of layered indium selenide (InSe) obtained by mechanical exfoliation (ME). The two-photon absorption (TPA) effect of layered InSe was tested using micro-Z/I-scan techniques. The results indicate that InSe flakes undergo the TPA response under the excitation of both 520 nm and 1040 nm fs pulses, and that InSe is more likely to achieve TPA saturation under visible light excitation. Furthermore, ultrafast carrier dynamics revealed that InSe flakes in the visible region undergo a transition from photoinduced absorption to photobleaching and exhibit a fast recombination time of ∼0.4–1ps, suggesting a high optical modulation speed as high as ∼1–2.5 THz.

Cooperite, or platinum sulfide (PtS), is a rare mineral that generally exists as microscale, irregularly shaped crystallites. The presence of impurities, in both naturally occurring and synthesized samples, has hindered the study of its optical properties in the past. In this work, we prepare large-scale, uniform PtS films in bulk to two-dimensional form through the thermally assisted conversion method. An abnormal trend is observed in linear spectral studies whereby the optical bandgap narrows as the film thickness decreases. A model based on the continuous distribution of carriers in real space, which can be regarded as a quantum well normal to the plane, is used to describe the thickness-dependent carrier recombination phenomenon. In the nonlinear optical measurements, PtS exhibits ultrafast saturable absorption and self-defocusing properties in the visible region, which are dominated by the resonant electronic nonlinearities.

Tellurium (Te) is a novel elementary material, which has recently attracted extensive attention due to its intriguing physical properties, such as topological, thermoelectric, and photoelectric properties. Further study on Te crystal structures will help to understand its properties and facilitate its application. Here, the angle-resolved polarized Raman spectroscopy has been employed to study Te crystal symmetry. Three different Raman vibration modes were obtained, each of which possess a different polarization dependence. Furthermore, it is revealed that Te nanosheets show a second-order harmonic response over a wide spectrum and have the greatest conversion efficiency at an excitation wavelength of 880 nm. Its second-order nonlinear susceptibility is estimated to be 2049 p m V − 1 . This substantial nonlinear optical response endows Te nanosheets with the potential for developing nonlinear photonic and optoelectronic nanodevices with high efficiency.

The dramatic enhancement of charge carrier interaction makes many-body effects of great prominence in two-dimensional materials. Here we report the defect-assisted Auger scattering combined with band-to-band Auger recombination as playing the dominant recovery mechanism in the charge carriers of atomically thin-layered ReS2. Time resolved transient absorption spectra investigation reveals two different decay processes over the visible and near- infrared range, which is attributed to the shallow and deep defects introduced by the existence of sulfur (S) vacancy. A rate equation system is invoked to rationalize our peculiar pump and temperature dependence of carrier dynamics quantitatively. These findings provide theoretical insights into the significant role played by nonradiative Auger processes and may pave the way for the development of diverse ReS2-based high performance photonic and optoelectronic devices.

In this work, γ-graphyne (γ-GY), a novel two-dimensional (2D) carbon allotrope, is demonstrated to have excellent ultrafast saturable absorption properties superior to that of graphene in the near infrared region. For practical application, the γ-GY nanosheets were directly dispersed in toluene in the existence of polymer, and were easily fabricated into flexible thin films. As proof-of-concept, the performances of γ-GY as a saturable absorber in passively Q-switched lasers and in all-optical switches were investigated. A minimum pulse width of 241 ns with the maximum pulse energy of 0.76 µJ and the corresponding peak power of 3.15 W was achieved for a γ-GY Q-switched solid-state laser at 1.06 µm. The γ-GY all-optical switching shows a rising/falling time of 1.46 ms/ 2.13 ms.

Using a 2.3 mm thick KBe(2)BO(3)F(2) crystal optically contacted with CaF(2) in a prism-coupled device, we have obtained an average output power of as much as 360 mW at 200 nm. Long-term stability was verified above a 150 mW level at 200 nm. An output power of 50 mW was also obtained with a narrow spectral width of 0.007 pm at 193.5 nm.