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

We report experimental studies of spatial self-phase modulation (SSPM) in liquid suspensions of semiconducting MoS2, MoSe2, MoTe2, WS2, semimetallic ZrTe2, WTe2, and metallic NbS2, NbSe2 using linearly and circularly polarized light with CW or CW-mode-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 similar to 4.3 x 10(-7) to similar to 4.2 x 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 NbS2, ZrTe2, and WTe2.

Automated summary

We experimentally studied spatial self-phase modulation (SSPM) in liquid suspensions of various 2D materials. The intensity-dependent changes in refractive index responsible for SSPM are shown to be due to thermal effects. The measured thermal nonlinear coefficients for different suspensions are independent of the excitation regime. The use of circularly polarized light complements the results obtained with linearly polarized light.