Modulation of the nonlinear optical response and transient dynamics of CdO/Ag/CdO sandwich-type films

Sandwich-type materials with tunable optical response and enhanced optical nonlinearity are of great importance for future nanophotonic devices. Herein, we investigate the third-order nonlinear optical response and transient dynamics of a series of CdO/Ag/CdO sandwich-type films with different Ag sputtering time. SEM images demonstrate that the Ag layer in CdO/Ag/CdO sandwich-type films change from a nanoisland to semicontinuous film with increase of Ag sputtering time. Z-scan measurements indicate that the CdO/Ag/CdO sandwich-type films exhibit huge nonlinear optical response on both femtosecond and picosecond time regime. The maximum nonlinear absorption coefficient (& beta; = 1.605 x 10-8m/W) and nonlinear refractive index (n2 = -6.70 x 10-15m2/W) of the CdO/Ag/CdO film with 4 min Ag sputtering time are obtained in picosecond Z-scan, which are about 17 and 10 times greater than that of the single-layer CdO, respectively. Transient absorption spectroscopy results confirm the effect of increased CdO/Ag/CdO interface binding on the thermal electron transfer mechanism. A model is proposed to describe the ultrafast dynamic processes in the CdO/Ag/CdO sandwich-type films. Our results indicate the CdO/Ag/CdO sandwich-type films with tailored nonlinear optical properties are highly promising for applications of optical switches devices.