Giant saturation absorption of tungsten trioxide film prepared based on the seedless layer hydrothermal method

Nonlinear materials have gained wide interest as saturable absorbers and pulse compression for pulsed laser applications due to their unique optical properties. This work investigates the third-order nonlinear phenomenon of tungsten trioxide (WO 3 ) thin films. The giant nonlinear absorption and nonlinear refractive index of WO 3 thin films were characterized by Z -scan method at 800 nm. We experimentally observed the giant saturable absorption (SA) and nonlinear refractive index of WO 3 thin films prepared by the seedless layer hydrothermal method, with SA coefficient being as high as –2.59 × 10 5 cm⋅GW −1 . The SA coefficient is at least one order of magnitude larger than those of the conventional semiconductors. The nonlinear refractive index n 2 of WO 3 film has been observed for the first time in recent studies and the corresponding coefficient can be up to 1.793 cm 2 ⋅GW −1 . The large third-order nonlinear optical (NLO) response enables WO 3 thin films to be promising candidates for optoelectronic and photonic applications in the near-infrared domain.