Third‐Order Nonlinear Optical Response of Few‐Layer MXene Nb₂C and Applications for Square‐Wave Laser Pulse Generation

Abstract

optical computers, optical switches, pulsed laser generation, optical sensors, etc. As the fundamental information carrier of NLO, nonlinear optical materials have attracted great attention since the advent of the first laser and always been the research hotspot for material and optical scientists. In the last two decades, 2D materials, representative of the main including graphene, [1-3] topological insulators (TIs), [4-6] transition metal disulfides (TMDs) [7,8] and black phosphorus (BP), [9-11] have experienced an explosive growth because of the advantages of exotic optical, electronic, chemical, and mechanical properties that much differ from their bulk counterparts. Especially, the low dimensions and distinctive nonlinear optical properties make them strongly meet the ever-increasing demand and widely used in high efficiency, compactness, broadband optoelectronic and photonic devices, broadband all-optical modulator, optical frequency conversion, pulsed laser generation, surface plasmonic, and so on. [12-19] However, there are still some disadvantages for the current 2D materials. For example, the gapless band structure and relative low light absorption of graphene limit its extensive applications; [20,21] the band gap of TMDs (1.0-2.0 eV) indicates they cannot be available in mid-infrared wavelength range; [22,23] and easy oxidation is the biggest obstacle for practical applications of BP. [24,25] Therefore, it is still an urgent demand to explore promising novel 2D nonlinear optical materials. Recently, 2D MXenes have been extensively studied due to the unique optical and electronic properties. [26,27] MXene represents a large family of 2D transition metal carbides, carbonitrides, and nitrides, with the general formula of M n+1 X n T n (n = 1-3), where M represents a transition metal (e.g., Ti, Mo, Nb), X for either C and/or N, and T is the surface functional group (e.g.,-OH,-O, and-F). [28,29] Until now, more than 30 varieties of 2D MXenes have been synthesized and theoretically and experimentally studied, [30-34] revealing the outstanding features of metallic conductivity, large electric capacity, high mechanical strength, tunable band gap, high stability, high optical transparency, and large optical nonlinearities of MXenes. [35,36] Nb 2 C is a newly discovered 2D MXene with special band structure near the Fermi level, showing the great potential applications as electrode materials Niobium carbide (Nb 2 C), a newly developed 2D MXene material, has attracted much attention due to its outstanding electronic and optical properties. In this work, few-layer 2D Nb 2 C nanosheets are synthesized by magnetron sputtering deposition method. Z-scan measurements with pump source operating at 1.0 µm are performed to study the third-order nonlinear optical response, revealing excellent light modulation capabilities of 2D Nb 2 C. The effective nonlinear absorption coefficient (β eff ≈-10 5 cm GW-1) caused by saturable absorption effect is determined to be two orders of magnitude larger than that induced by reverse sat...

MOF‐Derived Porous Dodecahedron rGO‐Co3O4 for Robust Pulse Generation

“…[ 36–38 ] There is also a square wave pulse (SWP) in the negative dispersion region, and its pulse energy increases with the increase of the pump energy, so as to obtain a high‐energy pulsed laser output, while the peak power is mainly fixed. [ 39 ] Compared with SA prepared by traditional industrial methods, such as SESAM, which has a relatively high production cost, a complicated process and a narrow bandwidth when used for saturable absorption and it is only used in the near‐infrared band. This defect hinders the development of ultrafast lasers.…”

2D Transition Metal Carbides (MXenes) for Third Order Nonlinear Optics: Status and Prospects

“…The reports of Jiang et al [105] and Lee et al [19] proved this point, strongly singlephoton transition-induced saturable absorption resulted in a negative n 2 . Nevertheless, the report of Li et al [124] exhibited an opposite result, the saturable absorption led to a positive n 2 . This may hide a physical mechanism to be unveiled.…”

“…The obtained n 2 was on the order of 10 −20 m 2 W −1 , corresponding to the Re𝜒 (3) values on the order of 10 −16 esu. The NLO refraction of Nb 2 C MXenes was investigated by Li et al [124] through a closed aperture Z-scan (Figure 8b). Interestingly, the Re𝜒 (3) of Nb 2 C MXenes at 1064 nm was determined to be on the order of 10 −7 esu.…”

“…Interestingly, the Re𝜒 (3) of Nb 2 C MXenes at 1064 nm was determined to be on the order of 10 −7 esu. [124] The NLO refraction of V 2 C MXenes was studied by Lee et al [19] at 1900 nm with a closedaperture Z-scan, the nonlinear refractive indices of V 2 C were determined to be −0.61 cm 2 GW −1 . As discussed by Boyd et al, [81] a single photon transition generally led to a negative n 2 because the single photon resonance will partially exhaust the ground state, resulting in a decrease in molecular polarizability.…”

Generation of h–Shaped pulse in a mode–Locked erbium-doped fiber laser

“…The PPC effect contributes to the formation of h-shaped pulses and inhibits pulse splitting by flattening the lengthy trailing section [15]. Meanwhile, the PPC effect is associated with the nonlinearity in the laser resonant cavity, which implies the intensive nonlinearity can reduce the switching threshold [29]. As seen in Figure 5A, the intensity of corresponding output spectra increases slightly as the pump power increases, while the central wavelength remains almost invariable, which is consistent with the previously proven features of an h-shaped pulse [14,20,30,21,15].…”