Nonlinear optical studies of tungsten disulphide (WS${}_2$)/gold nanoparticles (AuNPs) using infrared femtosecond laser

We report on the observation of the nonlinear optical properties of tungsten disulphide (WS${}_2$) in the infrared (IR) region, along with the enhancement in the nonlinearity achieved by integrating gold nanoparticles (AuNPs) in WS${}_2$. WS${}_2$ was synthesized using liquid phase exfoliation (LPE) and the spray pyrolysis technique, with layers integrated of AuNPs synthesized using de-wetting process. All samples were characterized using FESEM-EDX, AFM, UV-Vis, and Raman Spectroscopy to analyze their properties including their morphology and linear absorption, in addition to band-gap and vibrational analyses. The nonlinear optical (NLO) measurements and analysis were conducted using the Z-scan technique with a 1560 nm femtosecond laser with both on open and closed apertures to determine the nonlinear absorption coefficient (β) and nonlinear refractive index (n${}_2$).Samples of WS${}_2$ and AuNPs-WS${}_2$ were compared for their coefficient values. AuNPs-WS${}_2$ obtained higher values of β${}_{avg\_}$S1= (2.30 ± 0.06) ×10${}^{-9}$ m/W and β${}_{avg\_}$S2= (4.45 ± 0.07) ×10${}^{-9}$ m/W resulting in a higher nonlinear optical susceptibility of χ${}^{\left(3\right)}$ = 10.20 × 10${}^{-12}$ esu, which is double that of WS${}_2$-only sample. This enhancement could be significant contribution in optical devices application.