Third-order nonlinear optical properties of WTe2 films synthesized by pulsed laser deposition

Abstract

The prominent third-order nonlinear optical properties of WTe2 films are studied through the Z-scan technique using a femtosecond pulsed laser at 1030 nm. Open-aperture (OA) and closed-aperture (CA) Z-scan measurements are performed at different intensities to investigate the nonlinear absorption and refraction properties of WTe2 films. OA Z-scan results show that WTe2 films always hold a saturable absorption characteristic without transition to reverse saturable absorption. Further, a large nonlinear absorption coefficient β is determined to be −3.37×103 cm/GW by fitting the OA Z-scan curve at the peak intensity of 15.603 GW/cm2. In addition, through the slow saturation absorption model, the ground state absorption cross section, excited state absorption cross section, and absorber’s density were found to be 1.4938×10−16 cm2, 1.2536×10−16 cm2, and 6.2396×1020 cm−3, respectively. CA Z-scan results exhibit a classic peak–valley shape of the CA Z-scan signal, which reveals a self-defocusing optical effect of WTe2 films under the measured environment. Furthermore, a considerable nonlinear refractive index value n2 can be obtained at −1.629×10−2 cm2/GW. Ultimately, the values of the real and imaginary parts of the third-order nonlinear susceptibility of WTe2 are roughly estimated to be −5.93×10−9 and −1.01×10−8 esu with the help of first-principles calculations. WTe2 possesses sizeable third-order nonlinear coefficients compared with other materials, which suggests that it has great potential to improve performance in nonlinear optical devices.