Intensity-Dependent Thermally Induced Nonlinear Optical Response of Two-Dimensional Layered Transition-Metal Dichalcogenides in Suspension

Abstract

We report experimental studies of spatial self-phase modulation (SSPM) in liquid suspensions of semiconducting MoS 2 , MoSe 2 , MoTe 2 , WS 2 , semimetallic ZrTe 2 , WTe 2 , and metallic NbS 2 , NbSe 2 using linearly and circularly polarized light with CW or CWmode-locked (ML) excitation lasers. For the semiconducting suspension of nanoflakes, excitation above and below the bandgap was performed. The results show that the intensity-dependent changes in the refractive index responsible for SSPM and associated ring formation are explained as arising from thermal origin. Measured values of the effective thermal nonlinear coefficient, n 2,th , range from ∼4.3 × 10 −7 to ∼4.2 × 10 −5 cm 2 /W, depending on the absorption strength of the suspension, and are independent of the optical excitation regime (polarization and laser mode of operation). The use of circularly polarized light to obtain the same results as seen with linearly polarized light is fundamental to complement the results, demonstrating that at the spectro-temporal regimes studied, thermal nonlinearity explains well the ring formation, in addition to providing the original SSPM results for NbS 2 , ZrTe 2 , and WTe 2 .

Spatial Self-Phase Modulation of Optical Vortex Beams in Liquid Suspensions of Semiconducting, Semimetallic, and Metallic 2D Nanoflakes due to a Kerr-like Nonlinearity

“…A ML Ti:sapphire laser (150 fs, 76 MHz) was employed. Despite the temporal regime being different from the experiments at 532 nm (CW for 532 nm, ML for 790 nm), the results are comparable since there is no significant difference in the SSPM results when either a CW or an ML laser with high repetition rate (∼MHz) is employed, as demonstrated by Bautista et al in ref . Figure shows experimental results for the suspension of MoS 2 .…”

“…Looking at Figure a, the absorbance of the samples at 532 nm follows this same ordering, which suggests that the nonlinearity is related to the linear absorbance of the samples. As thoroughly discussed in ref , this is an indication that the nonlinear response has a predominant thermal contribution. In this context, the role of the flakes is to enhance the absorbance of the liquid suspensions in certain spectral regions in comparison with the pure solvent, which may heat the samples, leading to the emergence of thermal nonlinearities.…”

“…25 This result is supported by Melhado et al, 26 which showed that electronic and orientational nonlinear effects are polarization-dependent, while thermal nonlinearities are not, an indication that the observed nonlinearities in our experiments are most likely of thermal origin. In a recent work, Bautista et al 20 discussed in detail the physical mechanisms responsible for SSPM of Gaussian beams interacting with liquid suspensions of 2D materials when CW or ML high repetition-rate lasers are employed. It was observed a clear correlation between the absorbance of the samples and the amplitude of the nonlinear response, concluding that the thermal effects play a predominant role in the SSPM observed.…”

Nonlinear Optical Properties of 2D CdSe Nanoplatelets in a Nonresonant Regime

“…What we obtained in our experiments is the opposite (Figures a,c and a), revealing a positive nonlinear refractive index dominated by the materials’ electronic nonlinear response. An intensity-dependent thermally induced optical nonlinearity in liquid suspensions of 2D materials is discussed throughout in the ref …”

Strong non-linear optical response of Sb2Se3 nanorods in a liquid suspension based on spatial self-phase modulation and their all-optical photonic device applications

“…Following this, there was a significant increase in research interest towards investigating the nonlinear properties of 2D layered materials using the SSPM technique due to its ability to facilitate strong light-matter interaction, effective bandgap modulation, and superior optoelectronic properties. 1,[17][18][19] It is essential to note that the SSPM diffraction ring pattern originates from the external electric field associated with the strong laser beam, which is explained by electron coherence theory. 4,[20][21][22] The origin of the SSPM diffraction ring pattern in 3D TaAs is attributed to laser induced hole coherence.…”