Nonlinear optical response spatial self-phase modulation in MoTe₂: correlations between χ⁽³⁾ and mobility or effective mass

Abstract

We report an unambiguous observation of third-order nonlinear optical effect, spatial self-phase modulation (SSPM), in a MoTe 2 dispersion. The values of the third order nonlinear optical coefficients effectively for one layer MoTe 2 , χ (3) one-layer , are obtained through the SSPM method at excitation wavelengths 473, 532, 750 and 801 nm, respectively. The wind-chime model is used to explain the ring formation time. The wavelength dependence of χ (3) one-layer compares well with the photo-absorption spectra. Significantly, we find a correlation between χ (3) and the carrier mobility μ or effective mass m * , which again further supports the laser-induced ac electron coherence in 2D materials.

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“…Thus far, SSPM has become a typical effective means to characterize 2D materials' nonlinear optical response. The n 2 (nonlinear refractive index) and v 3 ð Þ (third-order nonlinear susceptibility) of numerous materials, including graphene [14], tellurium [15], mote 2 [16], antimonene [17], etc., have been obtained by this method.…”

Recent Advances in Spatial Self‐Phase Modulation with 2D Materials and its Applications

“…The time evolution of the diffraction ring number ( N ) can be fitted by an exponential decay model, , where τ rise is the rise time for ring formations, and A denotes a constant. [ 44 ] According to the wind chime model proposed by Zhao et al., the formation time of the diffraction ring is described as , where ε r is the relative dielectric constant of the 2D material, η is the viscosity coefficient of the solvent, ξ is the fluid property of the 2D material, R is the average radius of the nanosheet disk, and I is the laser intensity. [ 24 ] The SSPM effect of most materials is almost instantaneous; however, this is not the case in some photopolymers (e.g., organ siloxanes).…”

“…achieved nonlinear tuning of the broadband nonlinear refractive index in the time dimension, with the maximum approaching 90% (Figure 2i). [ 162 ] Although the formation time of the SSPM effect can be changed, [ 44 ] the nonlinear tuning in the time dimension remains difficult to control. The same effect can be achieved at the temperature scale, which may be caused by thermally induced nonlinearity or bubble scattering (Figure 2j).…”

“…Recently, Zhao's team found that the effective mass of electrons and the carrier mobility depend on χ 3 strictly by summarizing some of SSPM's work (Figure 6f,g). [ 44 ] The SSPM relation to electrons is crucial evidence for the pure coherence theory.…”

“…In this review, first we summarize the current use of the SSPM to investigate the third‐order nonlinear optical response of 2D materials. The nonlinear refractive index of 2D materials, such as graphene (≈10 −7 cm 2 W −1 ), [ 22 ] MoS 2 (≈10 −9 cm 2 W −1 ), [ 24 ] MoSe 2 (≈10 −4 cm 2 W −1 ), [ 42 ] WSe 2 (≈10 −10 cm 2 W −1 ), [ 43 ] MoTe 2 (≈10 −12 cm 2 W −1 ), [ 44 ] Ti 3 C 2 T x (≈10 −4 cm 2 W −1 ), [ 45 ] graphdiyne (≈10 −5 cm 2 W −1 ), InSe (≈10 −5 cm 2 W −1 ), [ 46 ] boron (≈10 −6 cm 2 W −1 ) [ 47 ] were experimentally determined by the SSPM. The current research hotspots of the SSPM are discussed, such as tuning of the nonlinear refractive index and investigation of the band gap.…”