Abstract
The nonlinear optical properties and ultrafast dynamics process of Au@Ag coreshell nanospheres (NSs) are reported in this paper. We researched the optical nonlinear absorption property of Au@Ag coreshell NSs excited by 800 nm laser at different energies by open-aperture Z-scan technology. The experimental results demonstrated that the Au@Ag coreshell NSs exhibited two-phone absorption (TPA) behavior, the degree of which was intensity-dependent. The TPA coefficients of Au@Ag coreshell NSs excited by different energies were obtained by fitting. By using pump-probe technology, we studied the ultrafast dynamics process of Au@Ag coreshell NSs. The results indicated that the relaxation process contained a fast and a slow process, which depended strongly on the laser intensity. By numerical fitting, we got the relaxation times of the sample excited at different laser powers.
Highlights
The optical nonlinearity of gold or silver nanoparticles with different morphologies has been extensively studied in recent years, such as nanospheres (NSs),7–11 nanorods,12–15 nanocages,16,17 nanotriangles,18–21 nanodiscs,22 and nanotubes
When the sample comes toward the focal point, the normalized transmittance decreases gradually, and the degree of decrease in normalized transmittance is related to the power intensities; the higher the power intensity is, the greater the degree of decrease in normalized transmittance is
That is the nonlinear absorption behavior of Au@Ag coreshell NSs is caused by two-photon absorption, which is consistent with that reported in Ref. 28
Summary
Especially gold and silver nanostructures, have attracted great research interest for their strong local surface plasmon resonance (LSPR) effect, which may lead to enhanced nonlinearity of metal nanoparticles. The optical nonlinearity of gold or silver nanoparticles with different morphologies has been extensively studied in recent years, such as nanospheres (NSs), nanorods, nanocages, nanotriangles, nanodiscs, and nanotubes. In the process of research, it was found that the application scope of single component nanoparticles was limited, so people changed the research direction to coreshell nanoparticles. Seo et al studied the nonlinear optical properties of Au/Ag coreshells and Au nanoparticles excited by a 532 nm nanosecond laser using Z-scan technology.. Ferreira et al successfully synthesized Au@Ag bimetallic nanoparticles by a seed-mediated method and determined their nonlinear optical properties by Z-scan technology with an argon continuous-wave (CW) laser of variable power at 514 nm.. Most of the known investigations on the nonlinear optical properties of Au@Ag coreshell nanoparticles were conducted under picosecond or nanosecond laser pulses. It is more valuable to use ultrashort laser pulses, such as femtosecond pulses, to research the nonlinear optical properties of Au@Ag coreshell nanoparticles. The femtosecond optical nonlinear absorption properties and ultrafast dynamics process of Au@Ag coreshell NSs were researched by OA Z-scan technology and the femtosecond pump-probe technique, respectively. The TPA coefficients and the relaxation times of Au@Ag coreshell NSs were obtained by numerical fitting
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