Here, we report hitherto unobserved local field (LF)-assisted pump wavelength-dependent nonlinear optical (NLO) effects of three-photon (3PA)-induced four-photon absorption (4PA) at 532 nm and two-photon-induced 3PA at 730 nm in triangular-shaped core–shell Ag-Au nanoparticles (TrAg@Au) by femtosecond Z-scan. The shell thickness-dependent enhancement in the LF is observed by a COMSOL simulation. The intensity-dependent interplay between saturable and reverse-saturable absorptions along with switching of nonlinear (NL) phase is reported at 730 nm, showing the superiority of TrAg@Au in optical switching (OS). The optical limiting (OL) threshold ($F$th) of ${5.9}\;({6.5})\;{\rm{mJ}}/{{\rm{cm}}^2}$ at 730 (532) nm boost their potential over benchmarked materials.

中文翻译：

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Au涂层三角形Ag-Au纳米结构中不寻常的高阶非线性光学特性

在这里，我们报告了迄今为止未观察到的局部场 (LF) 辅助泵浦波长相关非线性光学 (NLO) 效应的三光子 (3PA) 诱导四光子吸收 (4PA) 在 532 nm 和两光子诱导 3PA 在730 nm 在三角形核壳 Ag-Au 纳米粒子 (TrAg@Au) 中通过飞秒 Z 扫描。通过 COMSOL 仿真观察到 LF 中壳厚度相关的增强。在 730 nm 处报道了可饱和和反饱和吸收以及非线性 (NL) 相位切换之间的强度相关相互作用，表明 TrAg@Au 在光切换 (OS) 中的优越性。光限幅（OL）的阈值（$ F $的TH）$ {5.9} \;（{6.5}）\ {\ RM {毫焦耳}} / {{\ RM {厘米}} ^ 2} $ 730（ 532) nm 提高了它们在基准材料上的潜力。