Ultrafast nonlinear optical response in tungsten sulfide (WS2) nanospheres

In this present work, we have found saturable absorption (SA) and large nonlinear refractive index of Tungsten Sulfide (WS2) nanospheres (average diameter 90 nm) using open aperture (OA) and close aperture (CA) Z-scan technique with the mode-locked femtosecond laser. The measured saturation intensity (Is) of 471 GW/cm2 is attributed to the trapstate. Transient absorption pump-probe studies reveal an excitonic lifetime of 1.1 ± 0.1 ps which confirms the trapstate bleach of WS2 nanospheres. Additionally, closed aperture Z-scan measurement unveiled the nonlinear refractive index (n2) of 5.1×10−16 cm2/W. This positive nonlinear refractive index of spherical WS2 nanostructure suggests that this is a promising material for ultrafast optical switching.